how to Json encode in yii2?

Question

Attempting to encode json and receive 400: Bad Request in yii2. I am trying to encode in Rest client but it is not working properly.

<?php 
    namespace app\controllers;
    use Yii;
    use yii\filters\AccessControl;
    use yii\web\Controller;
    use yii\filters\VerbFilter;
    use app\models\TblUserRegistration;
    class UserController extends Controller
    {
        public function actionRegister()
        {
            $model = new TblUserRegistration();
            $username = $_POST['username'];
            echo json_encode($username);
        }
    }
?>

Error image.

Error image

Answer 1

public function actionRegister()
{
    \Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
    $model = new TblUserRegistration();
    return $_POST['username'];
}    

Answer 2

Solution 1: In case if all your controller's actions will deliver json you may also consider extanding yii\rest\Controller instead of yii\web\Controller :

namespace app\controllers;

use Yii;

class UserController extends \yii\rest\Controller
{
    public function actionRegister()
    {
        $username = Yii::$app->request->post('username');
        return $username;
    }
}

NOTE: you may also use ActiveController which extends yii\rest\Controller (see rest docs) if you need to handle CRUD operations.

---

Solution 2: A different approach when extending yii\web\Controller is by using yii\filters\ContentNegotiator. Note that setting $enableCsrfValidation to false may be mandatory here as it is explained in its related docs :

Whether to enable CSRF (Cross-Site Request Forgery) validation. Defaults to true. When CSRF validation is enabled, forms submitted to an Yii Web application must be originated from the same application. If not, a 400 HTTP exception will be raised.

Note, this feature requires that the user client accepts cookie. Also, to use this feature, forms submitted via POST method must contain a hidden input whose name is specified by $csrfParam. You may use yii\helpers\Html::beginForm() to generate his hidden input.

The above code may be rewritten this way :

namespace app\controllers;

use Yii;
use yii\web\Controller;
use yii\filters\ContentNegotiator;
use yii\web\Response;

class UserController extends Controller
{
    public $enableCsrfValidation = false;

    public function behaviors()
    {
        return [
            'contentNegotiator' => [
                'class' => ContentNegotiator::className(),
                'formats' => [
                    'application/json' => Response::FORMAT_JSON,
                ],
                'only' => ['register'],
            ],
        ];
    }

    public function actionRegister()
    {
        $username = Yii::$app->request->post('username');
        return $username;
    }
}

Answer 3

i think 400 have nothing to do with json_encode

google "yii2 csrf" for more information.

public function actionRegister()
{
    // is not safe
    Yii::$app->controller->enableCsrfValidation = false;

    // set response header
    \Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
  
    $model = new TblUserRegistration();
    $username = $_POST['username'];
    return $username;
}

or add scrf in view: form:

<input name="_csrf" type="hidden" id="_csrf" value="<?= Yii::$app->request->csrfToken ?>">

meta:

<?= Html::csrfMetaTags() ?>