Adds actions to your `crud-json-api` controller to handle POST and PATCH relationships requests.

CrudJsonControllerTrait

<?php

namespace App\Traits;

use Cake\Utility\Inflector;
use Cake\Utility\Hash;

trait CrudJsonApiControllerTrait
{
    /**
     * related method
     * NB: requires a route matcher: $routes->connect('/{relation}/{id}/<table_name>', ['controller' => 'model_name', 'action' => 'related'], ['id' => '\d+', 'pass' => ['id', 'relation']]);
     * @return \Cake\Http\Response|null
     *
     */
    public function index()
    {
        $input_line = $this->request->getParam('_matchedRoute');

        preg_match('/\/([[a-zA-Z]*)\/]*:([a-zA-Z]*_id)\/[a-zA-Z]*/', $input_line, $output_array);
        if (!empty($output_array)) {
            $this->Crud->on('beforePaginate', function (\Cake\Event\Event $event) use ($output_array) {
                $event->getSubject()->query
                  ->innerJoinWith(ucfirst($output_array[1]))
                  ->where([ucfirst($output_array[1]) . '.id' => $this->request->getParam($output_array[2])]);
                $event->getSubject()->query->first();
            });
        }
        return parent::index();
    }

    /**
     * JSONAPI spec for POST relationships is enabled here via `beforeFind` and `beforeSave` hooks.
     * @todo: this would probably be better as a custom Action (https://github.com/FriendsOfCake/crud-json-api/issues/118)
     */
    public function postrelationships()
    {
        $request = $this->request;
        $id = $request->getParam('id');
        $foreignTableName = $request->getParam('foreignTableName');
        $data = $request->getData();
        $requestMethod = $request->getMethod();

        $this->Crud->on('beforeFind', function (\Cake\Event\Event $event) use ($data, $foreignTableName, $requestMethod) {
            $query = $event->getSubject()->query;
            $query->contain(['Dishes']);
        });
        $this->Crud->on('afterFind', function (\Cake\Event\Event $event) use ($data, $foreignTableName, $requestMethod) {
            $entity = $event->getSubject()->entity;
        });

        // ensure that only adds new relationships, doesn't destroy old ones
        $this->Crud->on('beforeSave', function (\Cake\Event\Event $event) use ($id, $data, $foreignTableName) {
            $entity = $event->getSubject()->entity;
            $entity->$foreignTableName = empty($entity->$foreignTableName) ? [] : $entity->$foreignTableName;

            $ids = Hash::extract($entity->$foreignTableName, '{n}.id');
            foreach ($data['data'] as $key => $recordAttributes) {
                // get the related record
                $foreignTable = $this->getTableLocator()->get(Inflector::camelize($foreignTableName));
                $foreignKey = $foreignTableName . '.id';
                $query = $foreignTable->findAllById($recordAttributes['id']);
                $foreignRecord = $query->first();
                // push it onto the relationsships array
                if (!empty($foreignRecord)) {
                    if (in_array($foreignRecord->id, $ids)) {
                        // don't add id's that are already added
                    } else {
                        array_push($entity->$foreignTableName, $foreignRecord);
                    }
                }
            }
        });
        return parent::edit($id);
    }

    /**
     * @todo: this would probably be better as a custom Action (https://github.com/FriendsOfCake/crud-json-api/issues/117)
     */
    public function updaterelationships()
    {
        $request = $this->request;
        $id = $request->getParam('id');
        $foreignTableName = $request->getParam('foreignTableName');
        $data = $request->getData();

        $this->Crud->on('beforeSave', function (\Cake\Event\Event $event) use ($data, $foreignTableName) {
            // Allow all relationships to be removed, as per 1.0 JSONAPI spec https://jsonapi.org/format/#crud-updating-to-many-relationships
            $entity = $event->getSubject()->entity;
            if (empty((array)$data['data'])) {
                $entity->$foreignTableName = [];
            } else {
                $entity->$foreignTableName = [];

                foreach ($data['data'] as $key => $recordAttributes) {
                    // get the related record
                    $foreignTable = $this->getTableLocator()->get(Inflector::camelize($foreignTableName));
                    $foreignKey = $foreignTableName . '.id';
                    $query = $foreignTable->findAllById($recordAttributes['id']);
                    $foreignRecord = $query->first();
                    // push it onto the relationsships array if it exists
                    if (!empty($foreignRecord)) {
                        array_push($entity->$foreignTableName, $foreignRecord);
                    }
                }
            }
        });

        return parent::edit($id);
    }
}