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Fetch Operation

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About

This operation allows an EntityCrudController to respond to AJAX requests with entries in the database for a different entity, in a format that can be used by the relationship, select2_from_ajax and select2_from_ajax_multiple fields.

Requirements

None.

How to Use

In order to enable this operation in your CrudController, you need to:

1. Use the FetchOperation trait;
2. Add a fetchEntityName() method, that will respond to the AJAX requests (following this naming convention);

    use \Backpack\CRUD\app\Http\Controllers\Operations\FetchOperation;

    protected function fetchTag()
    {
        return $this->fetch(\App\Models\Tag::class);
    }

To customize the FetchOperation, pass an array to the fetch() call, rather than a class name. For example:

<?php

namespace App\Http\Controllers\Admin;

use Backpack\CRUD\app\Http\Controllers\CrudController;

class ProductCrudController extends CrudController
{
    use \Backpack\CRUD\app\Http\Controllers\Operations\FetchOperation;

    protected function fetchTag()
    {
        return $this->fetch([
            'model' => \App\Models\Tag::class, // required
            'searchable_attributes' => ['name', 'description'],
            'paginate' => 10, // items to show per page
            'query' => function($model) {
                return $model->active();
            } // to filter the results that are returned
        ]);
    }
}

3. A route following has been created automatically to point to the fetchTag method you created. You now point your AJAX select to this route, using backpack_url('your-main-entity/fetch/tag') .

How It Works

Based on the fact that the fetchTag() method exist, the Fetch operation will create a /product/fetch/tag POST route, which points to fetchTag(). Inside fetchTag() we call fetch(), that responds with entries in the format select2 needs.

Preventing FetchOperation of guessing the searchable attributes

If not specified searchable_attributes will be automatically infered from model dabatase columns. To prevent this behaviour you can setup an empty searchable_attributes array.

That said, you can use something like below:

public function fetchUser() {
        return $this->fetch([
            'model' => User::class,
            'query' => function($model) {
                $search = request()->input('q') ?? false;
                if ($search) {
                    return $model->whereRaw('CONCAT(`first_name`," ",`last_name`) LIKE "%' . $search . '%"');
                }else{
                    return $model;
                }
            },
            'searchable_attributes' => []
        ]);
    }

Using FetchOperation with select2_ajax filter

The FetchOperation can also be used as the source URL for the select2_ajax filter. To do that, we need to:

• change the AJAX method from GET (the default for this filter) to POST (the default for the Fetch operation);
• tell the filter what attribute we want to show to the user;

$this->crud->addFilter([
  'name'        => 'category_id',
  'type'        => 'select2_ajax',
  'label'       => 'Category',
  'placeholder' => 'Pick a category',
  'method' => 'POST', // mandatory change
  // 'select_attribute' => 'name' // the attribute that will be shown to the user by default 'name'
  // 'select_key' => 'id' // by default is ID, change it if your model uses some other key
],
backpack_url('product/fetch/category'), // the fetch route on the ProductCrudController 
function($value) { // if the filter is active
    // $this->crud->addClause('where', 'category_id', $value);
});

How to Overwrite

In case you need to change how this operation works, it's best to take a look at the FetchOperation.php trait to understand how it works. It's a pretty simple operation. Most common ways to overwrite the Fetch operation are documented below:

Custom behaviour for one fetch method

To make a fetchCategory() method behave differently, you can copy-paste the logic inside the FetchOperation::fetch() and change it to do whatever you need. Instead of returning $this->fetch() you can return your own results.

Custom behaviour for multiple fetch methods inside a Controller

To make all calls to fetch() inside an EntityCrudController behave differently, you can easily overwrite the fetch() method in that controller:

use \Backpack\CRUD\app\Http\Controllers\Operations\FetchOperation;

public function fetch($arg)
{
    // your custom code here
}

Then all $this->fetch() calls from that Controller will be using your custom code.

In case you need to call the original fetch() method (from the trait) inside your custom fetch() method (inside the controller), you can do:

use \Backpack\CRUD\app\Http\Controllers\Operations\FetchOperation { fetch as traitFetch; }

public function fetch($arg)
{
    // your custom code here

    // call the method in the trait
    return $this->traitFetch();
}

Custom behaviour for all fetch calls, in all Controllers

If you want all your fetch() calls to behave differently, no matter what Controller they are in, you can:

• duplicate the FetchOperation trait inside your application;
• instead of using \Backpack\CRUD\app\Http\Controllers\Operations\FetchOperation inside your controllers, use your custom operation trait;