add nova

nova/src/Fields/ResolvesReverseRelation.php

@@ -0,0 +1,98 @@
+<?php
+
+namespace Laravel\Nova\Fields;
+
+use Illuminate\Database\Eloquent\Relations\Relation;
+use Laravel\Nova\Http\Requests\NovaRequest;
+
+trait ResolvesReverseRelation
+{
+    /**
+     * The reverse relation for the related resource.
+     *
+     * @var string|null
+     */
+    public $reverseRelation;
+
+    /**
+     * Determine if the field is the reverse relation of a showed index view.
+     *
+     * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
+     * @return bool
+     */
+    public function isReverseRelation(NovaRequest $request)
+    {
+        if (! $request->viaResource || ($this->resourceName && $this->resourceName !== $request->viaResource)) {
+            return false;
+        }
+
+        $reverse = $this->getReverseRelation($request);
+
+        return $reverse === $request->viaRelationship;
+    }
+
+    /**
+     * Get reverse relation field name.
+     *
+     * @param  \Laravel\Nova\Http\Requests\NovaRequest  $request
+     * @return string
+     */
+    public function getReverseRelation(NovaRequest $request)
+    {
+        if (is_null($this->reverseRelation)) {
+            $viaModel = forward_static_call(
+                [$resourceClass = $request->viaResource(), 'newModel']
+            );
+
+            $viaResource = new $resourceClass($viaModel);
+
+            $resource = $request->newResource();
+
+            $this->reverseRelation = $viaResource->availableFields($request)
+                    ->filter(function ($field) use ($viaModel, $resource) {
+                        if (! isset($field->resourceName) || $field->resourceName !== $resource::uriKey()) {
+                            return false;
+                        }
+
+                        if (! $field instanceof MorphMany
+                            && ! $field instanceof HasMany
+                            && ! $field instanceof HasOne) {
+                            return false;
+                        }
+
+                        if ($field instanceof HasOne && $field->ofManyRelationship()) {
+                            return false;
+                        }
+
+                        $model = $resource->model();
+
+                        if (! method_exists($viaModel, $field->attribute) || ! method_exists($model, $this->attribute)) {
+                            return false;
+                        }
+
+                        $relation = $viaModel->{$field->attribute}();
+
+                        return $this->getRelationForeignKeyName($relation) === $this->getRelationForeignKeyName(
+                            $resource->model()->{$this->attribute}()
+                        );
+                    })->first(function ($field) use ($request) {
+                        return $field->attribute === $request->viaRelationship;
+                    })->attribute ?? '';
+        }
+
+        return $this->reverseRelation;
+    }
+
+    /**
+     * Get foreign key name for relation.
+     *
+     * @param  \Illuminate\Database\Eloquent\Relations\Relation  $relation
+     * @return string
+     */
+    protected function getRelationForeignKeyName(Relation $relation)
+    {
+        return method_exists($relation, 'getForeignKeyName')
+            ? $relation->getForeignKeyName()
+            : $relation->getForeignKey();
+    }
+}