feat(graphql): add support for graphql context propagation

Signed-off-by: Raymond Feng <[email protected]>

examples/graphql/src/application.ts

@@ -5,10 +5,10 @@
 
 import {BootMixin} from '@loopback/boot';
 import {ApplicationConfig} from '@loopback/core';
+import {GraphQLBindings, GraphQLComponent} from '@loopback/graphql';
 import {RepositoryMixin} from '@loopback/repository';
 import {RestApplication} from '@loopback/rest';
 import path from 'path';
-import {GraphQLBindings, GraphQLComponent} from '@loopback/graphql';
 import {sampleRecipes} from './sample-recipes';
 
 export {ApplicationConfig};
@@ -26,6 +26,11 @@ export class GraphqlDemoApplication extends BootMixin(
       asMiddlewareOnly: true,
     });
 
+    // It's possible to register a graphql context resolver
+    this.bind(GraphQLBindings.GRAPHQL_CONTEXT_RESOLVER).to(context => {
+      return {...context};
+    });
+
     this.bind('recipes').to([...sampleRecipes]);
 
     // Set up default home page

examples/graphql/src/datasources/recipes.datasource.ts

@@ -28,7 +28,8 @@ const config = {
     [ContextTags.NAMESPACE]: RepositoryBindings.DATASOURCES,
   },
 })
-export class RecipesDataSource extends juggler.DataSource
+export class RecipesDataSource
+  extends juggler.DataSource
   implements LifeCycleObserver {
   static dataSourceName = 'recipes';
   static readonly defaultConfig = config;

examples/graphql/src/graphql-resolvers/recipe-resolver.ts

@@ -3,14 +3,16 @@
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
 
-import {service} from '@loopback/core';
+import {inject, service} from '@loopback/core';
 import {
   arg,
   fieldResolver,
+  GraphQLBindings,
   Int,
   mutation,
   query,
   resolver,
+  ResolverData,
   ResolverInterface,
   root,
 } from '@loopback/graphql';
@@ -27,6 +29,8 @@ export class RecipeResolver implements ResolverInterface<Recipe> {
     @repository('RecipeRepository')
     private readonly recipeRepo: RecipeRepository,
     @service(RecipeService) private readonly recipeService: RecipeService,
+    // It's possible to inject the resolver data
+    @inject(GraphQLBindings.RESOLVER_DATA) private resolverData: ResolverData,
   ) {}
 
   @query(returns => Recipe, {nullable: true})

extensions/graphql/README.md

@@ -256,6 +256,8 @@ export class RecipeResolver implements ResolverInterface<Recipe> {
     @repository('RecipeRepository')
     private readonly recipeRepo: RecipeRepository,
     @service(RecipeService) private readonly recipeService: RecipeService,
+    // It's possible to inject the resolver data
+    @inject(GraphQLBindings.RESOLVER_DATA) private resolverData: ResolverData,
   ) {}
 }
 ```
@@ -265,6 +267,47 @@ export class RecipeResolver implements ResolverInterface<Recipe> {
 The `GraphQLComponent` contributes a booter that discovers and registers
 resolver classes from `src/graphql-resolvers` during `app.boot()`.
 
+## Propagate context data
+
+The `GraphQLServer` allows you to propagate context from Express to resolvers.
+
+### Register a GraphQL context resolver
+
+```ts
+export class GraphqlDemoApplication extends BootMixin(
+  RepositoryMixin(RestApplication),
+) {
+  constructor(options: ApplicationConfig = {}) {
+    super(options);
+
+    // ...
+    // It's possible to register a graphql context resolver
+    this.bind(GraphQLBindings.GRAPHQL_CONTEXT_RESOLVER).to(context => {
+      // Add your custom logic here to produce a context from incoming ExpressContext
+      return {...context};
+    });
+  }
+  // ...
+}
+```
+
+### Access the GraphQL context inside a resolver
+
+```ts
+@resolver(of => Recipe)
+export class RecipeResolver implements ResolverInterface<Recipe> {
+  constructor(
+    // constructor injection of service
+    @repository('RecipeRepository')
+    private readonly recipeRepo: RecipeRepository,
+    @service(RecipeService) private readonly recipeService: RecipeService,
+    // It's possible to inject the resolver data
+    @inject(GraphQLBindings.RESOLVER_DATA) private resolverData: ResolverData,
+  ) {}
+  // ...
+}
+```
+
 ## Try it out
 
 Check out

extensions/graphql/src/graphql.container.ts

@@ -82,9 +82,9 @@ export class LoopBackContainer implements ContainerType {
     debug(
       'Resolver %s found in context %s',
       resolverClass.name,
-      this.ctx.name,
+      resolutionCtx.name,
       found,
     );
-    return this.ctx.getValueOrPromise(found.key);
+    return resolutionCtx.getValueOrPromise(found.key);
   }
 }

extensions/graphql/src/graphql.server.ts

@@ -17,12 +17,18 @@ import {
   Server,
 } from '@loopback/core';
 import {HttpOptions, HttpServer} from '@loopback/http-server';
+import {ContextFunction} from 'apollo-server-core';
 import {ApolloServer, ApolloServerExpressConfig} from 'apollo-server-express';
+import {ExpressContext} from 'apollo-server-express/dist/ApolloServer';
 import express from 'express';
 import {buildSchema, NonEmptyArray, ResolverInterface} from 'type-graphql';
 import {LoopBackContainer} from './graphql.container';
 import {GraphQLBindings, GraphQLTags} from './keys';
 
+export {ContextFunction} from 'apollo-server-core';
+export {ApolloServerExpressConfig} from 'apollo-server-express';
+export {ExpressContext} from 'apollo-server-express/dist/ApolloServer';
+
 /**
  * Options for GraphQL server
  */
@@ -95,9 +101,16 @@ export class GraphQLServer extends Context implements Server {
       container: new LoopBackContainer(this),
     });
 
-    const serverConfig = {
+    // Allow a graphql context resolver to be bound to GRAPHQL_CONTEXT_RESOLVER
+    const graphqlContextResolver: ContextFunction<ExpressContext> =
+      (await this.get(GraphQLBindings.GRAPHQL_CONTEXT_RESOLVER, {
+        optional: true,
+      })) ?? (context => context);
+
+    const serverConfig: ApolloServerExpressConfig = {
       // enable GraphQL Playground
       playground: true,
+      context: graphqlContextResolver,
       ...this.options.graphql,
       schema,
     };

extensions/graphql/src/keys.ts

@@ -6,7 +6,7 @@
 import {BindingKey, Constructor} from '@loopback/core';
 import {ResolverData} from 'type-graphql';
 import {GraphQLComponent} from './graphql.component';
-import {GraphQLServer} from './graphql.server';
+import {ContextFunction, ExpressContext, GraphQLServer} from './graphql.server';
 
 export namespace GraphQLBindings {
   export const GRAPHQL_SERVER = BindingKey.create<GraphQLServer>(
@@ -17,6 +17,10 @@ export namespace GraphQLBindings {
     'components.GraphQLComponent',
   );
 
+  export const GRAPHQL_CONTEXT_RESOLVER = BindingKey.create<
+    ContextFunction<ExpressContext>
+  >('graphql.contextResolver');
+
   export const RESOLVER_DATA = BindingKey.create<ResolverData<unknown>>(
     'graphql.resolverData',
   );