From 1dcc3d1cd26497494f0492cee03c18e3cd344f2f Mon Sep 17 00:00:00 2001
From: Christopher Gammie <contact@gammie.co.uk>
Date: Sat, 19 Aug 2023 15:30:35 +0100
Subject: [PATCH] feat: add attach relationship command

---
 .../AttachRelationshipImplementation.php      |  59 ++++
 src/Core/Auth/ResourceAuthorizer.php          |  40 +++
 .../AttachRelationshipCommand.php             | 141 +++++++++
 .../AttachRelationshipCommandHandler.php      | 101 +++++++
 .../HandlesAttachRelationshipCommands.php     |  33 +++
 .../AuthorizeAttachRelationshipCommand.php    |  58 ++++
 .../TriggerAttachRelationshipHooks.php        |  63 +++++
 src/Core/Bus/Commands/Dispatcher.php          |   3 +
 .../ValidateRelationshipCommand.php           |   3 +-
 src/Core/Http/Hooks/HooksImplementation.php   |  35 ++-
 src/Core/Store/Store.php                      |  12 +-
 .../AttachRelationshipCommandHandlerTest.php  | 167 +++++++++++
 ...AuthorizeAttachRelationshipCommandTest.php | 257 +++++++++++++++++
 .../TriggerAttachRelationshipHooksTest.php    | 196 +++++++++++++
 .../ValidateRelationshipCommandTest.php       |  34 ++-
 .../Http/Hooks/HooksImplementationTest.php    | 267 ++++++++++++++++++
 16 files changed, 1457 insertions(+), 12 deletions(-)
 create mode 100644 src/Contracts/Http/Hooks/AttachRelationshipImplementation.php
 create mode 100644 src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommand.php
 create mode 100644 src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandler.php
 create mode 100644 src/Core/Bus/Commands/AttachRelationship/HandlesAttachRelationshipCommands.php
 create mode 100644 src/Core/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommand.php
 create mode 100644 src/Core/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooks.php
 create mode 100644 tests/Unit/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandlerTest.php
 create mode 100644 tests/Unit/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommandTest.php
 create mode 100644 tests/Unit/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooksTest.php

diff --git a/src/Contracts/Http/Hooks/AttachRelationshipImplementation.php b/src/Contracts/Http/Hooks/AttachRelationshipImplementation.php
new file mode 100644
index 0000000..75c012b
--- /dev/null
+++ b/src/Contracts/Http/Hooks/AttachRelationshipImplementation.php
@@ -0,0 +1,59 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Contracts\Http\Hooks;
+
+use Illuminate\Http\Exceptions\HttpResponseException;
+use Illuminate\Http\Request;
+use LaravelJsonApi\Contracts\Query\QueryParameters;
+
+interface AttachRelationshipImplementation
+{
+    /**
+     * @param object $model
+     * @param string $fieldName
+     * @param Request $request
+     * @param QueryParameters $query
+     * @return void
+     * @throws HttpResponseException
+     */
+    public function attachingRelationship(
+        object $model,
+        string $fieldName,
+        Request $request,
+        QueryParameters $query,
+    ): void;
+
+    /**
+     * @param object $model
+     * @param string $fieldName
+     * @param mixed $related
+     * @param Request $request
+     * @param QueryParameters $query
+     * @return void
+     * @throws HttpResponseException
+     */
+    public function attachedRelationship(
+        object $model,
+        string $fieldName,
+        mixed $related,
+        Request $request,
+        QueryParameters $query,
+    ): void;
+}
diff --git a/src/Core/Auth/ResourceAuthorizer.php b/src/Core/Auth/ResourceAuthorizer.php
index d0d0685..13dea69 100644
--- a/src/Core/Auth/ResourceAuthorizer.php
+++ b/src/Core/Auth/ResourceAuthorizer.php
@@ -342,6 +342,46 @@ public function updateRelationshipOrFail(?Request $request, object $model, strin
         }
     }
 
+    /**
+     * Authorize a JSON:API attach relationship command.
+     *
+     * @param Request|null $request
+     * @param object $model
+     * @param string $fieldName
+     * @return ErrorList|null
+     * @throws AuthorizationException
+     * @throws AuthenticationException
+     * @throws HttpExceptionInterface
+     */
+    public function attachRelationship(?Request $request, object $model, string $fieldName): ?ErrorList
+    {
+        $passes = $this->authorizer->attachRelationship(
+            $request,
+            $model,
+            $fieldName,
+        );
+
+        return $passes ? null : $this->failed();
+    }
+
+    /**
+     * Authorize a JSON:API attach relationship command, or fail.
+     *
+     * @param Request|null $request
+     * @param object $model
+     * @param string $fieldName
+     * @return void
+     * @throws AuthorizationException
+     * @throws AuthenticationException
+     * @throws HttpExceptionInterface
+     */
+    public function attachRelationshipOrFail(?Request $request, object $model, string $fieldName): void
+    {
+        if ($errors = $this->attachRelationship($request, $model, $fieldName)) {
+            throw new JsonApiException($errors);
+        }
+    }
+
     /**
      * @return ErrorList
      * @throws AuthorizationException
diff --git a/src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommand.php b/src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommand.php
new file mode 100644
index 0000000..f65bf56
--- /dev/null
+++ b/src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommand.php
@@ -0,0 +1,141 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Bus\Commands\AttachRelationship;
+
+use Illuminate\Http\Request;
+use LaravelJsonApi\Contracts\Http\Hooks\AttachRelationshipImplementation;
+use LaravelJsonApi\Core\Bus\Commands\Command\Command;
+use LaravelJsonApi\Core\Bus\Commands\Command\HasQuery;
+use LaravelJsonApi\Core\Bus\Commands\Command\Identifiable;
+use LaravelJsonApi\Core\Bus\Commands\Command\IsRelatable;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceId;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceType;
+use LaravelJsonApi\Core\Extensions\Atomic\Operations\UpdateToMany;
+use LaravelJsonApi\Core\Support\Contracts;
+
+class AttachRelationshipCommand extends Command implements IsRelatable
+{
+    use Identifiable;
+    use HasQuery;
+
+    /**
+     * @var AttachRelationshipImplementation|null
+     */
+    private ?AttachRelationshipImplementation $hooks = null;
+
+    /**
+     * Fluent constructor
+     *
+     * @param Request|null $request
+     * @param UpdateToMany $operation
+     * @return self
+     */
+    public static function make(?Request $request, UpdateToMany $operation): self
+    {
+        return new self($request, $operation);
+    }
+
+    /**
+     * AttachRelationshipCommand constructor
+     *
+     * @param Request|null $request
+     * @param UpdateToMany $operation
+     */
+    public function __construct(?Request $request, private readonly UpdateToMany $operation)
+    {
+        Contracts::assert(
+            $this->operation->isAttachingRelationship(),
+            'Expecting a to-many operation that is to attach resources to a relationship.',
+        );
+
+        parent::__construct($request);
+    }
+
+    /**
+     * @inheritDoc
+     * @TODO support operation with a href.
+     */
+    public function type(): ResourceType
+    {
+        $type = $this->operation->ref()?->type;
+
+        assert($type !== null, 'Expecting an update relationship operation with a ref.');
+
+        return $type;
+    }
+
+    /**
+     * @inheritDoc
+     * @TODO support operation with a href
+     */
+    public function id(): ResourceId
+    {
+        $id = $this->operation->ref()?->id;
+
+        assert($id !== null, 'Expecting an update relationship operation with a ref that has an id.');
+
+        return $id;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function fieldName(): string
+    {
+        $fieldName = $this->operation->ref()?->relationship ?? $this->operation->href()?->getRelationshipName();
+
+        assert(
+            is_string($fieldName),
+            'Expecting update relationship operation to have a field name.',
+        );
+
+        return $fieldName;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function operation(): UpdateToMany
+    {
+        return $this->operation;
+    }
+
+    /**
+     * Set the hooks implementation.
+     *
+     * @param AttachRelationshipImplementation|null $hooks
+     * @return $this
+     */
+    public function withHooks(?AttachRelationshipImplementation $hooks): self
+    {
+        $copy = clone $this;
+        $copy->hooks = $hooks;
+
+        return $copy;
+    }
+
+    /**
+     * @return AttachRelationshipImplementation|null
+     */
+    public function hooks(): ?AttachRelationshipImplementation
+    {
+        return $this->hooks;
+    }
+}
diff --git a/src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandler.php b/src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandler.php
new file mode 100644
index 0000000..4f0e82a
--- /dev/null
+++ b/src/Core/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandler.php
@@ -0,0 +1,101 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Bus\Commands\AttachRelationship;
+
+use LaravelJsonApi\Contracts\Store\Store;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware\AuthorizeAttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware\TriggerAttachRelationshipHooks;
+use LaravelJsonApi\Core\Bus\Commands\Middleware\SetModelIfMissing;
+use LaravelJsonApi\Core\Bus\Commands\Middleware\ValidateRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+use LaravelJsonApi\Core\Extensions\Atomic\Results\Result as Payload;
+use LaravelJsonApi\Core\Support\Contracts;
+use LaravelJsonApi\Core\Support\PipelineFactory;
+use UnexpectedValueException;
+
+class AttachRelationshipCommandHandler
+{
+    /**
+     * AttachRelationshipCommandHandler constructor
+     *
+     * @param PipelineFactory $pipelines
+     * @param Store $store
+     */
+    public function __construct(
+        private readonly PipelineFactory $pipelines,
+        private readonly Store $store,
+    ) {
+    }
+
+    /**
+     * Execute an attach relationship command.
+     *
+     * @param AttachRelationshipCommand $command
+     * @return Result
+     */
+    public function execute(AttachRelationshipCommand $command): Result
+    {
+        $pipes = [
+            SetModelIfMissing::class,
+            AuthorizeAttachRelationshipCommand::class,
+            ValidateRelationshipCommand::class,
+            TriggerAttachRelationshipHooks::class,
+        ];
+
+        $result = $this->pipelines
+            ->pipe($command)
+            ->through($pipes)
+            ->via('handle')
+            ->then(fn (AttachRelationshipCommand $cmd): Result => $this->handle($cmd));
+
+        if ($result instanceof Result) {
+            return $result;
+        }
+
+        throw new UnexpectedValueException('Expecting pipeline to return a command result.');
+    }
+
+    /**
+     * Handle the command.
+     *
+     * @param AttachRelationshipCommand $command
+     * @return Result
+     */
+    private function handle(AttachRelationshipCommand $command): Result
+    {
+        $fieldName = $command->fieldName();
+        $validated = $command->validated();
+
+        Contracts::assert(
+            array_key_exists($fieldName, $validated),
+            sprintf('Relation %s must have a validation rule so that it is validated.', $fieldName)
+        );
+
+        $input = $validated[$command->fieldName()];
+        $model = $command->modelOrFail();
+
+        $result = $this->store
+            ->modifyToMany($command->type(), $model, $fieldName)
+            ->withRequest($command->request())
+            ->attach($input);
+
+        return Result::ok(new Payload($result, true));
+    }
+}
diff --git a/src/Core/Bus/Commands/AttachRelationship/HandlesAttachRelationshipCommands.php b/src/Core/Bus/Commands/AttachRelationship/HandlesAttachRelationshipCommands.php
new file mode 100644
index 0000000..e167648
--- /dev/null
+++ b/src/Core/Bus/Commands/AttachRelationship/HandlesAttachRelationshipCommands.php
@@ -0,0 +1,33 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Bus\Commands\AttachRelationship;
+
+use Closure;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+
+interface HandlesAttachRelationshipCommands
+{
+    /**
+     * @param AttachRelationshipCommand $command
+     * @param Closure $next
+     * @return Result
+     */
+    public function handle(AttachRelationshipCommand $command, Closure $next): Result;
+}
diff --git a/src/Core/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommand.php b/src/Core/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommand.php
new file mode 100644
index 0000000..fd99b7c
--- /dev/null
+++ b/src/Core/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommand.php
@@ -0,0 +1,58 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware;
+
+use Closure;
+use LaravelJsonApi\Core\Auth\ResourceAuthorizerFactory;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\HandlesAttachRelationshipCommands;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+
+class AuthorizeAttachRelationshipCommand implements HandlesAttachRelationshipCommands
+{
+    /**
+     * AuthorizeAttachRelationshipCommand constructor
+     *
+     * @param ResourceAuthorizerFactory $authorizerFactory
+     */
+    public function __construct(private readonly ResourceAuthorizerFactory $authorizerFactory)
+    {
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function handle(AttachRelationshipCommand $command, Closure $next): Result
+    {
+        $errors = null;
+
+        if ($command->mustAuthorize()) {
+            $errors = $this->authorizerFactory
+                ->make($command->type())
+                ->attachRelationship($command->request(), $command->modelOrFail(), $command->fieldName());
+        }
+
+        if ($errors) {
+            return Result::failed($errors);
+        }
+
+        return $next($command);
+    }
+}
diff --git a/src/Core/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooks.php b/src/Core/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooks.php
new file mode 100644
index 0000000..8fd8ad8
--- /dev/null
+++ b/src/Core/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooks.php
@@ -0,0 +1,63 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware;
+
+use Closure;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\HandlesAttachRelationshipCommands;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+use RuntimeException;
+
+class TriggerAttachRelationshipHooks implements HandlesAttachRelationshipCommands
+{
+    /**
+     * @inheritDoc
+     */
+    public function handle(AttachRelationshipCommand $command, Closure $next): Result
+    {
+        $hooks = $command->hooks();
+
+        if ($hooks === null) {
+            return $next($command);
+        }
+
+        $request = $command->request() ?? throw new RuntimeException('Hooks require a request to be set.');
+        $query = $command->query() ?? throw new RuntimeException('Hooks require a query to be set.');
+        $model = $command->modelOrFail();
+        $fieldName = $command->fieldName();
+
+        $hooks->attachingRelationship($model, $fieldName, $request, $query);
+
+        /** @var Result $result */
+        $result = $next($command);
+
+        if ($result->didSucceed()) {
+            $hooks->attachedRelationship(
+                $model,
+                $fieldName,
+                $result->payload()->data,
+                $request,
+                $query,
+            );
+        }
+
+        return $result;
+    }
+}
diff --git a/src/Core/Bus/Commands/Dispatcher.php b/src/Core/Bus/Commands/Dispatcher.php
index 65d970c..872d348 100644
--- a/src/Core/Bus/Commands/Dispatcher.php
+++ b/src/Core/Bus/Commands/Dispatcher.php
@@ -21,6 +21,8 @@
 
 use Illuminate\Contracts\Container\Container;
 use LaravelJsonApi\Contracts\Bus\Commands\Dispatcher as DispatcherContract;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommandHandler;
 use LaravelJsonApi\Core\Bus\Commands\Command\Command;
 use LaravelJsonApi\Core\Bus\Commands\Destroy\DestroyCommand;
 use LaravelJsonApi\Core\Bus\Commands\Destroy\DestroyCommandHandler;
@@ -75,6 +77,7 @@ private function handlerFor(string $commandClass): string
             UpdateCommand::class => UpdateCommandHandler::class,
             DestroyCommand::class => DestroyCommandHandler::class,
             UpdateRelationshipCommand::class => UpdateRelationshipCommandHandler::class,
+            AttachRelationshipCommand::class => AttachRelationshipCommandHandler::class,
             default => throw new RuntimeException('Unexpected command class: ' . $commandClass),
         };
     }
diff --git a/src/Core/Bus/Commands/Middleware/ValidateRelationshipCommand.php b/src/Core/Bus/Commands/Middleware/ValidateRelationshipCommand.php
index 1f932ee..7563035 100644
--- a/src/Core/Bus/Commands/Middleware/ValidateRelationshipCommand.php
+++ b/src/Core/Bus/Commands/Middleware/ValidateRelationshipCommand.php
@@ -24,6 +24,7 @@
 use LaravelJsonApi\Contracts\Validation\Container as ValidatorContainer;
 use LaravelJsonApi\Contracts\Validation\RelationshipValidator;
 use LaravelJsonApi\Contracts\Validation\ResourceErrorFactory;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
 use LaravelJsonApi\Core\Bus\Commands\Result;
 use LaravelJsonApi\Core\Bus\Commands\UpdateRelationship\HandlesUpdateRelationshipCommands;
 use LaravelJsonApi\Core\Bus\Commands\UpdateRelationship\UpdateRelationshipCommand;
@@ -48,7 +49,7 @@ public function __construct(
     /**
      * @inheritDoc
      */
-    public function handle(UpdateRelationshipCommand $command, Closure $next): Result
+    public function handle(UpdateRelationshipCommand|AttachRelationshipCommand $command, Closure $next): Result
     {
         if ($command->mustValidate()) {
             $validator = $this
diff --git a/src/Core/Http/Hooks/HooksImplementation.php b/src/Core/Http/Hooks/HooksImplementation.php
index 404a3f5..12b8aca 100644
--- a/src/Core/Http/Hooks/HooksImplementation.php
+++ b/src/Core/Http/Hooks/HooksImplementation.php
@@ -22,6 +22,7 @@
 use Illuminate\Contracts\Support\Responsable;
 use Illuminate\Http\Exceptions\HttpResponseException;
 use Illuminate\Http\Request;
+use LaravelJsonApi\Contracts\Http\Hooks\AttachRelationshipImplementation;
 use LaravelJsonApi\Contracts\Http\Hooks\DestroyImplementation;
 use LaravelJsonApi\Contracts\Http\Hooks\IndexImplementation;
 use LaravelJsonApi\Contracts\Http\Hooks\ShowImplementation;
@@ -43,7 +44,8 @@ class HooksImplementation implements
     DestroyImplementation,
     ShowRelatedImplementation,
     ShowRelationshipImplementation,
-    UpdateRelationshipImplementation
+    UpdateRelationshipImplementation,
+    AttachRelationshipImplementation
 {
     /**
      * HooksImplementation constructor
@@ -280,4 +282,35 @@ public function updatedRelationship(
 
         $this($method, $model, $related, $request, $query);
     }
+
+    /**
+     * @inheritDoc
+     */
+    public function attachingRelationship(
+        object $model,
+        string $fieldName,
+        Request $request,
+        QueryParameters $query,
+    ): void
+    {
+        $method = 'attaching' . Str::classify($fieldName);
+
+        $this($method, $model, $request, $query);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function attachedRelationship(
+        object $model,
+        string $fieldName,
+        mixed $related,
+        Request $request,
+        QueryParameters $query,
+    ): void
+    {
+        $method = 'attached' . Str::classify($fieldName);
+
+        $this($method, $model, $related, $request, $query);
+    }
 }
diff --git a/src/Core/Store/Store.php b/src/Core/Store/Store.php
index db41893..b7f25eb 100644
--- a/src/Core/Store/Store.php
+++ b/src/Core/Store/Store.php
@@ -221,7 +221,11 @@ public function delete(ResourceType|string $resourceType, $modelOrResourceId): v
     /**
      * @inheritDoc
      */
-    public function modifyToOne(string $resourceType, $modelOrResourceId, string $fieldName): ToOneBuilder
+    public function modifyToOne(
+        ResourceType|string $resourceType,
+        $modelOrResourceId,
+        string $fieldName,
+    ): ToOneBuilder
     {
         $repository = $this->resources($resourceType);
 
@@ -235,7 +239,11 @@ public function modifyToOne(string $resourceType, $modelOrResourceId, string $fi
     /**
      * @inheritDoc
      */
-    public function modifyToMany(string $resourceType, $modelOrResourceId, string $fieldName): ToManyBuilder
+    public function modifyToMany(
+        ResourceType|string $resourceType,
+        $modelOrResourceId,
+        string $fieldName,
+    ): ToManyBuilder
     {
         $repository = $this->resources($resourceType);
 
diff --git a/tests/Unit/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandlerTest.php b/tests/Unit/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandlerTest.php
new file mode 100644
index 0000000..3a2c854
--- /dev/null
+++ b/tests/Unit/Bus/Commands/AttachRelationship/AttachRelationshipCommandHandlerTest.php
@@ -0,0 +1,167 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Tests\Unit\Bus\Commands\AttachRelationship;
+
+use ArrayObject;
+use Illuminate\Contracts\Pipeline\Pipeline;
+use Illuminate\Http\Request;
+use LaravelJsonApi\Contracts\Store\Store as StoreContract;
+use LaravelJsonApi\Contracts\Store\ToManyBuilder;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommandHandler;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware\AuthorizeAttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware\TriggerAttachRelationshipHooks;
+use LaravelJsonApi\Core\Bus\Commands\Middleware\SetModelIfMissing;
+use LaravelJsonApi\Core\Bus\Commands\Middleware\ValidateRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+use LaravelJsonApi\Core\Document\Input\Values\ListOfResourceIdentifiers;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceId;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceType;
+use LaravelJsonApi\Core\Extensions\Atomic\Operations\UpdateToMany;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\OpCodeEnum;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\Ref;
+use LaravelJsonApi\Core\Support\PipelineFactory;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use stdClass;
+
+class AttachRelationshipCommandHandlerTest extends TestCase
+{
+    /**
+     * @var PipelineFactory&MockObject
+     */
+    private PipelineFactory&MockObject $pipelineFactory;
+
+    /**
+     * @var MockObject&StoreContract
+     */
+    private StoreContract&MockObject $store;
+
+    /**
+     * @var AttachRelationshipCommandHandler
+     */
+    private AttachRelationshipCommandHandler $handler;
+
+    /**
+     * @return void
+     */
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->handler = new AttachRelationshipCommandHandler(
+            $this->pipelineFactory = $this->createMock(PipelineFactory::class),
+            $this->store = $this->createMock(StoreContract::class),
+        );
+    }
+
+    /**
+     * @return void
+     */
+    public function test(): void
+    {
+        $operation = new UpdateToMany(
+            OpCodeEnum::Add,
+            new Ref(type: new ResourceType('posts'), id: new ResourceId('123'), relationship: 'tags'),
+            new ListOfResourceIdentifiers(),
+        );
+
+        $original = new AttachRelationshipCommand(
+            $request = $this->createMock(Request::class),
+            $operation,
+        );
+
+        $validated = [
+            'tags' => [
+                ['type' => 'tags', 'id' => '1'],
+                ['type' => 'tags', 'id' => '2'],
+            ],
+        ];
+
+        $passed = AttachRelationshipCommand::make($request, $operation)
+            ->withModel($model = new stdClass())
+            ->withValidated($validated);
+
+        $sequence = [];
+
+        $this->pipelineFactory
+            ->expects($this->once())
+            ->method('pipe')
+            ->with($this->identicalTo($original))
+            ->willReturn($pipeline = $this->createMock(Pipeline::class));
+
+        $pipeline
+            ->expects($this->once())
+            ->method('through')
+            ->willReturnCallback(function (array $actual) use (&$sequence, $pipeline): Pipeline {
+                $sequence[] = 'through';
+                $this->assertSame([
+                    SetModelIfMissing::class,
+                    AuthorizeAttachRelationshipCommand::class,
+                    ValidateRelationshipCommand::class,
+                    TriggerAttachRelationshipHooks::class,
+                ], $actual);
+                return $pipeline;
+            });
+
+        $pipeline
+            ->expects($this->once())
+            ->method('via')
+            ->with('handle')
+            ->willReturnCallback(function () use (&$sequence, $pipeline): Pipeline {
+                $sequence[] = 'via';
+                return $pipeline;
+            });
+
+        $pipeline
+            ->expects($this->once())
+            ->method('then')
+            ->willReturnCallback(function (\Closure $fn) use ($passed, &$sequence): Result {
+                $this->assertSame(['through', 'via'], $sequence);
+                return $fn($passed);
+            });
+
+        $this->store
+            ->expects($this->once())
+            ->method('modifyToMany')
+            ->with($this->identicalTo($passed->type()), $this->identicalTo($model), 'tags')
+            ->willReturn($builder = $this->createMock(ToManyBuilder::class));
+
+        $builder
+            ->expects($this->once())
+            ->method('withRequest')
+            ->with($this->identicalTo($request))
+            ->willReturnSelf();
+
+        $builder
+            ->expects($this->once())
+            ->method('attach')
+            ->with($this->identicalTo($validated['tags']))
+            ->willReturn($expected = new ArrayObject());
+
+        $payload = $this->handler
+            ->execute($original)
+            ->payload();
+
+        $this->assertTrue($payload->hasData);
+        $this->assertSame($expected, $payload->data);
+        $this->assertEmpty($payload->meta);
+    }
+}
diff --git a/tests/Unit/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommandTest.php b/tests/Unit/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommandTest.php
new file mode 100644
index 0000000..4c19491
--- /dev/null
+++ b/tests/Unit/Bus/Commands/AttachRelationship/Middleware/AuthorizeAttachRelationshipCommandTest.php
@@ -0,0 +1,257 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Tests\Unit\Bus\Commands\AttachRelationship\Middleware;
+
+use Illuminate\Auth\Access\AuthorizationException;
+use Illuminate\Http\Request;
+use LaravelJsonApi\Core\Auth\ResourceAuthorizer;
+use LaravelJsonApi\Core\Auth\ResourceAuthorizerFactory;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware\AuthorizeAttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+use LaravelJsonApi\Core\Document\ErrorList;
+use LaravelJsonApi\Core\Document\Input\Values\ListOfResourceIdentifiers;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceId;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceType;
+use LaravelJsonApi\Core\Extensions\Atomic\Operations\UpdateToMany;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\OpCodeEnum;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\Ref;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use stdClass;
+
+class AuthorizeAttachRelationshipCommandTest extends TestCase
+{
+    /**
+     * @var ResourceType
+     */
+    private ResourceType $type;
+
+    /**
+     * @var ResourceAuthorizerFactory&MockObject
+     */
+    private ResourceAuthorizerFactory&MockObject $authorizerFactory;
+
+    /**
+     * @var AuthorizeAttachRelationshipCommand
+     */
+    private AuthorizeAttachRelationshipCommand $middleware;
+
+    /**
+     * @return void
+     */
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->type = new ResourceType('posts');
+
+        $this->middleware = new AuthorizeAttachRelationshipCommand(
+            $this->authorizerFactory = $this->createMock(ResourceAuthorizerFactory::class),
+        );
+    }
+
+    /**
+     * @return void
+     */
+    public function testItPassesAuthorizationWithRequest(): void
+    {
+        $command = AttachRelationshipCommand::make(
+            $request = $this->createMock(Request::class),
+            new UpdateToMany(
+                OpCodeEnum::Add,
+                new Ref(type: $this->type, id: new ResourceId('123'), relationship: 'tags'),
+                new ListOfResourceIdentifiers(),
+            ),
+        )->withModel($model = new stdClass());
+
+        $this->willAuthorize($request, $model, 'tags', null);
+
+        $expected = Result::ok();
+
+        $actual = $this->middleware->handle($command, function ($cmd) use ($command, $expected): Result {
+            $this->assertSame($command, $cmd);
+            return $expected;
+        });
+
+        $this->assertSame($expected, $actual);
+    }
+
+    /**
+     * @return void
+     */
+    public function testItPassesAuthorizationWithoutRequest(): void
+    {
+        $command = AttachRelationshipCommand::make(
+            null,
+            new UpdateToMany(
+                OpCodeEnum::Add,
+                new Ref(type: $this->type, id: new ResourceId('123'), relationship: 'tags'),
+                new ListOfResourceIdentifiers(),
+            ),
+        )->withModel($model = new stdClass());
+
+        $this->willAuthorize(null, $model, 'tags', null);
+
+        $expected = Result::ok();
+
+        $actual = $this->middleware->handle($command, function ($cmd) use ($command, $expected): Result {
+            $this->assertSame($command, $cmd);
+            return $expected;
+        });
+
+        $this->assertSame($expected, $actual);
+    }
+
+    /**
+     * @return void
+     */
+    public function testItFailsAuthorizationWithException(): void
+    {
+        $command = AttachRelationshipCommand::make(
+            $request = $this->createMock(Request::class),
+            new UpdateToMany(
+                OpCodeEnum::Add,
+                new Ref(type: $this->type, id: new ResourceId('123'), relationship: 'tags'),
+                new ListOfResourceIdentifiers(),
+            ),
+        )->withModel($model = new stdClass());
+
+        $this->willAuthorizeAndThrow(
+            $request,
+            $model,
+            'tags',
+            $expected = new AuthorizationException('Boom!'),
+        );
+
+        try {
+            $this->middleware->handle(
+                $command,
+                fn() => $this->fail('Expecting next middleware to not be called.'),
+            );
+            $this->fail('Middleware did not throw an exception.');
+        } catch (AuthorizationException $actual) {
+            $this->assertSame($expected, $actual);
+        }
+    }
+
+    /**
+     * @return void
+     */
+    public function testItFailsAuthorizationWithErrorList(): void
+    {
+        $command = AttachRelationshipCommand::make(
+            $request = $this->createMock(Request::class),
+            new UpdateToMany(
+                OpCodeEnum::Add,
+                new Ref(type: $this->type, id: new ResourceId('123'), relationship: 'tags'),
+                new ListOfResourceIdentifiers(),
+            ),
+        )->withModel($model = new stdClass());
+
+        $this->willAuthorize($request, $model, 'tags', $expected = new ErrorList());
+
+        $result = $this->middleware->handle(
+            $command,
+            fn() => $this->fail('Expecting next middleware not to be called.'),
+        );
+
+        $this->assertTrue($result->didFail());
+        $this->assertSame($expected, $result->errors());
+    }
+
+    /**
+     * @return void
+     */
+    public function testItSkipsAuthorization(): void
+    {
+        $command = AttachRelationshipCommand::make(
+            $this->createMock(Request::class),
+            new UpdateToMany(
+                OpCodeEnum::Add,
+                new Ref(type: $this->type, id: new ResourceId('123'), relationship: 'tags'),
+                new ListOfResourceIdentifiers(),
+            ),
+        )->withModel(new stdClass())->skipAuthorization();
+
+
+        $this->authorizerFactory
+            ->expects($this->never())
+            ->method($this->anything());
+
+        $expected = Result::ok();
+
+        $actual = $this->middleware->handle($command, function ($cmd) use ($command, $expected): Result {
+            $this->assertSame($command, $cmd);
+            return $expected;
+        });
+
+        $this->assertSame($expected, $actual);
+    }
+
+    /**
+     * @param Request|null $request
+     * @param stdClass $model
+     * @param string $fieldName
+     * @param ErrorList|null $expected
+     * @return void
+     */
+    private function willAuthorize(?Request $request, stdClass $model, string $fieldName, ?ErrorList $expected): void
+    {
+        $this->authorizerFactory
+            ->expects($this->once())
+            ->method('make')
+            ->with($this->identicalTo($this->type))
+            ->willReturn($authorizer = $this->createMock(ResourceAuthorizer::class));
+
+        $authorizer
+            ->expects($this->once())
+            ->method('attachRelationship')
+            ->with($this->identicalTo($request), $this->identicalTo($model), $this->identicalTo($fieldName))
+            ->willReturn($expected);
+    }
+
+    /**
+     * @param Request|null $request
+     * @param stdClass $model
+     * @param string $fieldName
+     * @param AuthorizationException $expected
+     * @return void
+     */
+    private function willAuthorizeAndThrow(
+        ?Request $request,
+        stdClass $model,
+        string $fieldName,
+        AuthorizationException $expected,
+    ): void
+    {
+        $this->authorizerFactory
+            ->expects($this->once())
+            ->method('make')
+            ->with($this->identicalTo($this->type))
+            ->willReturn($authorizer = $this->createMock(ResourceAuthorizer::class));
+
+        $authorizer
+            ->expects($this->once())
+            ->method('attachRelationship')
+            ->with($this->identicalTo($request), $this->identicalTo($model), $this->identicalTo($fieldName))
+            ->willThrowException($expected);
+    }
+}
diff --git a/tests/Unit/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooksTest.php b/tests/Unit/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooksTest.php
new file mode 100644
index 0000000..7f053cf
--- /dev/null
+++ b/tests/Unit/Bus/Commands/AttachRelationship/Middleware/TriggerAttachRelationshipHooksTest.php
@@ -0,0 +1,196 @@
+<?php
+/*
+ * Copyright 2023 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\Core\Tests\Unit\Bus\Commands\AttachRelationship\Middleware;
+
+use ArrayObject;
+use Illuminate\Http\Request;
+use LaravelJsonApi\Contracts\Http\Hooks\AttachRelationshipImplementation;
+use LaravelJsonApi\Contracts\Query\QueryParameters;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\Middleware\TriggerAttachRelationshipHooks;
+use LaravelJsonApi\Core\Bus\Commands\Result;
+use LaravelJsonApi\Core\Document\Input\Values\ListOfResourceIdentifiers;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceId;
+use LaravelJsonApi\Core\Document\Input\Values\ResourceType;
+use LaravelJsonApi\Core\Extensions\Atomic\Operations\UpdateToMany;
+use LaravelJsonApi\Core\Extensions\Atomic\Results\Result as Payload;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\OpCodeEnum;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\Ref;
+use PHPUnit\Framework\TestCase;
+use stdClass;
+
+class TriggerAttachRelationshipHooksTest extends TestCase
+{
+    /**
+     * @var TriggerAttachRelationshipHooks
+     */
+    private TriggerAttachRelationshipHooks $middleware;
+
+    /**
+     * @return void
+     */
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->middleware = new TriggerAttachRelationshipHooks();
+    }
+
+    /**
+     * @return void
+     */
+    public function testItHasNoHooks(): void
+    {
+        $command = AttachRelationshipCommand::make(
+            $this->createMock(Request::class),
+            new UpdateToMany(
+                OpCodeEnum::Add,
+                new Ref(type: new ResourceType('posts'), id: new ResourceId('123'), relationship: 'tags'),
+                new ListOfResourceIdentifiers(),
+            ),
+        )->withModel(new stdClass());
+
+        $expected = Result::ok();
+
+        $actual = $this->middleware->handle(
+            $command,
+            function (AttachRelationshipCommand $cmd) use ($command, $expected): Result {
+                $this->assertSame($command, $cmd);
+                return $expected;
+            },
+        );
+
+        $this->assertSame($expected, $actual);
+    }
+
+    /**
+     * @return void
+     */
+    public function testItTriggersHooks(): void
+    {
+        $request = $this->createMock(Request::class);
+        $hooks = $this->createMock(AttachRelationshipImplementation::class);
+        $query = $this->createMock(QueryParameters::class);
+        $model = new stdClass();
+        $related = new ArrayObject();
+        $sequence = [];
+
+        $operation = new UpdateToMany(
+            OpCodeEnum::Add,
+            new Ref(type: new ResourceType('posts'), id: new ResourceId('123'), relationship: 'tags'),
+            new ListOfResourceIdentifiers(),
+        );
+
+        $command = AttachRelationshipCommand::make($request, $operation)
+            ->withModel($model)
+            ->withHooks($hooks)
+            ->withQuery($query);
+
+        $hooks
+            ->expects($this->once())
+            ->method('attachingRelationship')
+            ->willReturnCallback(function ($m, $f, $req, $q) use (&$sequence, $model, $request, $query): void {
+                $sequence[] = 'attaching';
+                $this->assertSame($model, $m);
+                $this->assertSame('tags', $f);
+                $this->assertSame($request, $req);
+                $this->assertSame($query, $q);
+            });
+
+        $hooks
+            ->expects($this->once())
+            ->method('attachedRelationship')
+            ->willReturnCallback(
+                function ($m, $f, $rel, $req, $q) use (&$sequence, $model, $related, $request, $query): void {
+                    $sequence[] = 'attached';
+                    $this->assertSame($model, $m);
+                    $this->assertSame('tags', $f);
+                    $this->assertSame($related, $rel);
+                    $this->assertSame($request, $req);
+                    $this->assertSame($query, $q);
+                },
+            );
+
+        $expected = Result::ok(new Payload($related, true));
+
+        $actual = $this->middleware->handle(
+            $command,
+            function (AttachRelationshipCommand $cmd) use ($command, $expected, &$sequence): Result {
+                $this->assertSame($command, $cmd);
+                $this->assertSame(['attaching'], $sequence);
+                return $expected;
+            },
+        );
+
+        $this->assertSame($expected, $actual);
+        $this->assertSame(['attaching', 'attached'], $sequence);
+    }
+
+    /**
+     * @return void
+     */
+    public function testItDoesNotTriggerAfterHooksIfItFails(): void
+    {
+        $request = $this->createMock(Request::class);
+        $hooks = $this->createMock(AttachRelationshipImplementation::class);
+        $query = $this->createMock(QueryParameters::class);
+        $model = new stdClass();
+        $sequence = [];
+
+        $operation = new UpdateToMany(
+            OpCodeEnum::Add,
+            new Ref(type: new ResourceType('posts'), id: new ResourceId('123'), relationship: 'tags'),
+            new ListOfResourceIdentifiers(),
+        );
+
+        $command = AttachRelationshipCommand::make($request, $operation)
+            ->withModel($model)
+            ->withHooks($hooks)
+            ->withQuery($query);
+
+        $hooks
+            ->expects($this->once())
+            ->method('attachingRelationship')
+            ->willReturnCallback(function ($m, $f, $req, $q) use (&$sequence, $model, $request, $query): void {
+                $sequence[] = 'attaching';
+                $this->assertSame($model, $m);
+                $this->assertSame('tags', $f);
+                $this->assertSame($request, $req);
+                $this->assertSame($query, $q);
+            });
+
+        $hooks
+            ->expects($this->never())
+            ->method('attachedRelationship');
+
+        $expected = Result::failed();
+
+        $actual = $this->middleware->handle(
+            $command,
+            function (AttachRelationshipCommand $cmd) use ($command, $expected, &$sequence): Result {
+                $this->assertSame($command, $cmd);
+                $this->assertSame(['attaching'], $sequence);
+                return $expected;
+            },
+        );
+
+        $this->assertSame($expected, $actual);
+        $this->assertSame(['attaching'], $sequence);
+    }
+}
diff --git a/tests/Unit/Bus/Commands/Middleware/ValidateRelationshipCommandTest.php b/tests/Unit/Bus/Commands/Middleware/ValidateRelationshipCommandTest.php
index aaed993..3c8165c 100644
--- a/tests/Unit/Bus/Commands/Middleware/ValidateRelationshipCommandTest.php
+++ b/tests/Unit/Bus/Commands/Middleware/ValidateRelationshipCommandTest.php
@@ -28,14 +28,18 @@
 use LaravelJsonApi\Contracts\Validation\Factory;
 use LaravelJsonApi\Contracts\Validation\RelationshipValidator;
 use LaravelJsonApi\Contracts\Validation\ResourceErrorFactory;
+use LaravelJsonApi\Core\Bus\Commands\AttachRelationship\AttachRelationshipCommand;
 use LaravelJsonApi\Core\Bus\Commands\Middleware\ValidateRelationshipCommand;
 use LaravelJsonApi\Core\Bus\Commands\Result;
 use LaravelJsonApi\Core\Bus\Commands\UpdateRelationship\UpdateRelationshipCommand;
 use LaravelJsonApi\Core\Document\ErrorList;
+use LaravelJsonApi\Core\Document\Input\Values\ListOfResourceIdentifiers;
 use LaravelJsonApi\Core\Document\Input\Values\ResourceId;
 use LaravelJsonApi\Core\Document\Input\Values\ResourceIdentifier;
 use LaravelJsonApi\Core\Document\Input\Values\ResourceType;
+use LaravelJsonApi\Core\Extensions\Atomic\Operations\UpdateToMany;
 use LaravelJsonApi\Core\Extensions\Atomic\Operations\UpdateToOne;
+use LaravelJsonApi\Core\Extensions\Atomic\Values\OpCodeEnum;
 use LaravelJsonApi\Core\Extensions\Atomic\Values\Ref;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
@@ -112,14 +116,25 @@ function (ResourceType $type, Request $request = null): UpdateRelationshipComman
                         new ResourceIdentifier(new ResourceType('users'), new ResourceId('456')),
                     );
 
-                    return UpdateRelationshipCommand::make($request, $operation);
+                    return new UpdateRelationshipCommand($request, $operation);
+                },
+            ],
+            'attach' => [
+                function (ResourceType $type, Request $request = null): AttachRelationshipCommand {
+                    $operation = new UpdateToMany(
+                        OpCodeEnum::Add,
+                        new Ref(type: $type, id: new ResourceId('123'), relationship: 'tags'),
+                        new ListOfResourceIdentifiers(),
+                    );
+
+                    return new AttachRelationshipCommand($request, $operation);
                 },
             ],
         ];
     }
 
     /**
-     * @param Closure<UpdateRelationshipCommand> $factory
+     * @param Closure(ResourceType, ?Request=): (UpdateRelationshipCommand|AttachRelationshipCommand) $factory
      * @return void
      * @dataProvider commandProvider
      */
@@ -153,7 +168,8 @@ public function testItPassesValidation(Closure $factory): void
 
         $actual = $this->middleware->handle(
             $command,
-            function (UpdateRelationshipCommand $cmd) use ($command, $validated, $expected): Result {
+            function (UpdateRelationshipCommand|AttachRelationshipCommand $cmd)
+            use ($command, $validated, $expected): Result {
                 $this->assertNotSame($command, $cmd);
                 $this->assertSame($validated, $cmd->validated());
                 return $expected;
@@ -164,7 +180,7 @@ function (UpdateRelationshipCommand $cmd) use ($command, $validated, $expected):
     }
 
     /**
-     * @param Closure<UpdateRelationshipCommand> $factory
+     * @param Closure(ResourceType, ?Request=): (UpdateRelationshipCommand|AttachRelationshipCommand) $factory
      * @return void
      * @dataProvider commandProvider
      */
@@ -205,7 +221,7 @@ public function testItFailsValidation(Closure $factory): void
     }
 
     /**
-     * @param Closure<UpdateRelationshipCommand> $factory
+     * @param Closure(ResourceType, ?Request=): (UpdateRelationshipCommand|AttachRelationshipCommand) $factory
      * @return void
      * @dataProvider commandProvider
      */
@@ -229,7 +245,8 @@ public function testItSetsValidatedDataIfNotValidating(Closure $factory): void
 
         $actual = $this->middleware->handle(
             $command,
-            function (UpdateRelationshipCommand $cmd) use ($command, $validated, $expected): Result {
+            function (UpdateRelationshipCommand|AttachRelationshipCommand $cmd)
+            use ($command, $validated, $expected): Result {
                 $this->assertNotSame($command, $cmd);
                 $this->assertSame($validated, $cmd->validated());
                 return $expected;
@@ -240,7 +257,7 @@ function (UpdateRelationshipCommand $cmd) use ($command, $validated, $expected):
     }
 
     /**
-     * @param Closure<UpdateRelationshipCommand> $factory
+     * @param Closure(ResourceType, ?Request=): (UpdateRelationshipCommand|AttachRelationshipCommand) $factory
      * @return void
      * @dataProvider commandProvider
      */
@@ -259,7 +276,8 @@ public function testItDoesNotValidateIfAlreadyValidated(Closure $factory): void
 
         $actual = $this->middleware->handle(
             $command,
-            function (UpdateRelationshipCommand $cmd) use ($command, $validated, $expected): Result {
+            function (UpdateRelationshipCommand|AttachRelationshipCommand $cmd)
+            use ($command, $validated, $expected): Result {
                 $this->assertSame($command, $cmd);
                 $this->assertSame($validated, $cmd->validated());
                 return $expected;
diff --git a/tests/Unit/Http/Hooks/HooksImplementationTest.php b/tests/Unit/Http/Hooks/HooksImplementationTest.php
index 193ae59..64a6a29 100644
--- a/tests/Unit/Http/Hooks/HooksImplementationTest.php
+++ b/tests/Unit/Http/Hooks/HooksImplementationTest.php
@@ -24,6 +24,7 @@
 use Illuminate\Contracts\Support\Responsable;
 use Illuminate\Http\Exceptions\HttpResponseException;
 use Illuminate\Http\Request;
+use LaravelJsonApi\Contracts\Http\Hooks\AttachRelationshipImplementation;
 use LaravelJsonApi\Contracts\Http\Hooks\DestroyImplementation;
 use LaravelJsonApi\Contracts\Http\Hooks\IndexImplementation;
 use LaravelJsonApi\Contracts\Http\Hooks\ShowImplementation;
@@ -2271,4 +2272,270 @@ public function updatedTags(
             $this->assertSame($response, $ex->getResponse());
         }
     }
+
+    /**
+     * @return void
+     */
+    public function testItInvokesAttachingRelationshipMethod(): void
+    {
+        $target = new class {
+            public ?stdClass $model = null;
+            public ?Request $request = null;
+            public ?QueryParameters $query = null;
+
+            public function attachingBlogPosts(
+                stdClass $model,
+                Request $request,
+                QueryParameters $query,
+            ): void
+            {
+                $this->model = $model;
+                $this->request = $request;
+                $this->query = $query;
+            }
+        };
+
+        $model = new stdClass();
+
+        $implementation = new HooksImplementation($target);
+        $implementation->attachingRelationship($model, 'blog-posts', $this->request, $this->query);
+
+        $this->assertInstanceOf(AttachRelationshipImplementation::class, $implementation);
+        $this->assertSame($model, $target->model);
+        $this->assertSame($this->request, $target->request);
+        $this->assertSame($this->query, $target->query);
+    }
+
+    /**
+     * @return void
+     */
+    public function testItInvokesAttachingRelationshipMethodAndThrowsResponse(): void
+    {
+        $response = $this->createMock(Response::class);
+
+        $target = new class($response) {
+            public ?stdClass $model = null;
+            public ?Request $request = null;
+            public ?QueryParameters $query = null;
+
+            public function __construct(private readonly Response $response)
+            {
+            }
+
+            public function attachingComments(
+                stdClass $model,
+                Request $request,
+                QueryParameters $query,
+            ): Response
+            {
+                $this->model = $model;
+                $this->request = $request;
+                $this->query = $query;
+
+                return $this->response;
+            }
+        };
+
+        $model = new stdClass();
+        $implementation = new HooksImplementation($target);
+
+        try {
+            $implementation->attachingRelationship($model, 'comments', $this->request, $this->query);
+            $this->fail('No exception thrown.');
+        } catch (HttpResponseException $ex) {
+            $this->assertSame($model, $target->model);
+            $this->assertSame($this->request, $target->request);
+            $this->assertSame($this->query, $target->query);
+            $this->assertSame($response, $ex->getResponse());
+        }
+    }
+
+    /**
+     * @return void
+     */
+    public function testItInvokesAttachingRelationshipMethodAndThrowsResponseFromResponsable(): void
+    {
+        $result = $this->createMock(Responsable::class);
+        $result
+            ->expects($this->once())
+            ->method('toResponse')
+            ->with($this->identicalTo($this->request))
+            ->willReturn($response = $this->createMock(Response::class));
+
+        $target = new class($result) {
+            public ?stdClass $model = null;
+            public ?Request $request = null;
+            public ?QueryParameters $query = null;
+
+            public function __construct(private readonly Responsable $result)
+            {
+            }
+
+            public function attachingTags(
+                stdClass $model,
+                Request $request,
+                QueryParameters $query,
+            ): Responsable
+            {
+                $this->model = $model;
+                $this->request = $request;
+                $this->query = $query;
+
+                return $this->result;
+            }
+        };
+
+        $model = new stdClass();
+        $implementation = new HooksImplementation($target);
+
+        try {
+            $implementation->attachingRelationship($model, 'tags', $this->request, $this->query);
+            $this->fail('No exception thrown.');
+        } catch (HttpResponseException $ex) {
+            $this->assertSame($model, $target->model);
+            $this->assertSame($this->request, $target->request);
+            $this->assertSame($this->query, $target->query);
+            $this->assertSame($response, $ex->getResponse());
+        }
+    }
+
+    /**
+     * @return void
+     */
+    public function testItInvokesAttachedRelationshipMethod(): void
+    {
+        $target = new class {
+            public ?stdClass $model = null;
+            public ?ArrayObject $related = null;
+            public ?Request $request = null;
+            public ?QueryParameters $query = null;
+
+            public function attachedBlogPosts(
+                stdClass $model,
+                ArrayObject $related,
+                Request $request,
+                QueryParameters $query,
+            ): void
+            {
+                $this->model = $model;
+                $this->related = $related;
+                $this->request = $request;
+                $this->query = $query;
+            }
+        };
+
+        $model = new stdClass();
+        $related = new ArrayObject();
+
+        $implementation = new HooksImplementation($target);
+        $implementation->attachedRelationship($model, 'blog-posts', $related, $this->request, $this->query);
+
+        $this->assertSame($model, $target->model);
+        $this->assertSame($related, $target->related);
+        $this->assertSame($this->request, $target->request);
+        $this->assertSame($this->query, $target->query);
+    }
+
+    /**
+     * @return void
+     */
+    public function testItInvokesAttachedRelationshipMethodAndThrowsResponse(): void
+    {
+        $response = $this->createMock(Response::class);
+
+        $target = new class($response) {
+            public ?stdClass $model = null;
+            public ?ArrayObject $related = null;
+            public ?Request $request = null;
+            public ?QueryParameters $query = null;
+
+            public function __construct(private readonly Response $response)
+            {
+            }
+
+            public function attachedComments(
+                stdClass $model,
+                ArrayObject $related,
+                Request $request,
+                QueryParameters $query,
+            ): Response
+            {
+                $this->model = $model;
+                $this->related = $related;
+                $this->request = $request;
+                $this->query = $query;
+
+                return $this->response;
+            }
+        };
+
+        $model = new stdClass();
+        $related = new ArrayObject();
+        $implementation = new HooksImplementation($target);
+
+        try {
+            $implementation->attachedRelationship($model, 'comments', $related, $this->request, $this->query);
+            $this->fail('No exception thrown.');
+        } catch (HttpResponseException $ex) {
+            $this->assertSame($model, $target->model);
+            $this->assertSame($related, $target->related);
+            $this->assertSame($this->request, $target->request);
+            $this->assertSame($this->query, $target->query);
+            $this->assertSame($response, $ex->getResponse());
+        }
+    }
+
+    /**
+     * @return void
+     */
+    public function testItInvokesAttachedRelationshipMethodAndThrowsResponseFromResponsable(): void
+    {
+        $result = $this->createMock(Responsable::class);
+        $result
+            ->expects($this->once())
+            ->method('toResponse')
+            ->with($this->identicalTo($this->request))
+            ->willReturn($response = $this->createMock(Response::class));
+
+        $target = new class($result) {
+            public ?stdClass $model = null;
+            public ?ArrayObject $related = null;
+            public ?Request $request = null;
+            public ?QueryParameters $query = null;
+
+            public function __construct(private readonly Responsable $result)
+            {
+            }
+
+            public function attachedTags(
+                stdClass $model,
+                ArrayObject $related,
+                Request $request,
+                QueryParameters $query,
+            ): Responsable
+            {
+                $this->model = $model;
+                $this->related = $related;
+                $this->request = $request;
+                $this->query = $query;
+
+                return $this->result;
+            }
+        };
+
+        $model = new stdClass();
+        $related = new ArrayObject();
+        $implementation = new HooksImplementation($target);
+
+        try {
+            $implementation->attachedRelationship($model, 'tags', $related, $this->request, $this->query);
+            $this->fail('No exception thrown.');
+        } catch (HttpResponseException $ex) {
+            $this->assertSame($model, $target->model);
+            $this->assertSame($related, $target->related);
+            $this->assertSame($this->request, $target->request);
+            $this->assertSame($this->query, $target->query);
+            $this->assertSame($response, $ex->getResponse());
+        }
+    }
 }