add files

src/Illuminate/Database/Eloquent/Relations/Concerns/SupportsDefaultModels.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Relations\Concerns;
+
+use Illuminate\Database\Eloquent\Model;
+
+trait SupportsDefaultModels
+{
+    /**
+     * Indicates if a default model instance should be used.
+     *
+     * Alternatively, may be a Closure or array.
+     *
+     * @var \Closure|array|bool
+     */
+    protected $withDefault;
+
+    /**
+     * Make a new related instance for the given model.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model  $parent
+     * @return \Illuminate\Database\Eloquent\Model
+     */
+    abstract protected function newRelatedInstanceFor(Model $parent);
+
+    /**
+     * Return a new model instance in case the relationship does not exist.
+     *
+     * @param  \Closure|array|bool  $callback
+     * @return $this
+     */
+    public function withDefault($callback = true)
+    {
+        $this->withDefault = $callback;
+
+        return $this;
+    }
+
+    /**
+     * Get the default value for this relation.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model  $parent
+     * @return \Illuminate\Database\Eloquent\Model|null
+     */
+    protected function getDefaultFor(Model $parent)
+    {
+        if (! $this->withDefault) {
+            return;
+        }
+
+        $instance = $this->newRelatedInstanceFor($parent);
+
+        if (is_callable($this->withDefault)) {
+            return call_user_func($this->withDefault, $instance) ?: $instance;
+        }
+
+        if (is_array($this->withDefault)) {
+            $instance->forceFill($this->withDefault);
+        }
+
+        return $instance;
+    }
+}