Souke/frontend/models/AddEtablissementForm.php

<?php

namespace frontend\models;

use Yii;
use yii\base\Model;
use common\models\UserEtablissement;

/**
 * ContactForm is the model behind the contact form.
 */
class AddEtablissementForm extends Model
{
    public $id_etablissement;

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            ['id_etablissement', 'required', 'message' => 'Champs obligatoire'],
        ];
    }

    /**
     * @inheritdoc
     */
    public function attributeLabels()
    {
        return [
        	'id_etablissement' => 'Ajouter une boulangerie',
        ];
    }

    /**
     * Sends an email to the specified email address using the information collected by this model.
     *
     * @param  string  $email the target email address
     * @return boolean whether the email was sent
     */
    public function add()
    {
        $user_etablissement_exist = UserEtablissement::find()
                ->where(['id_user'=>Yii::$app->user->identity->id, 'id_etablissement' =>$this->id_etablissement])
                ->one() ;
        
        if(!$user_etablissement_exist)
        {
            $user_etablissement = new UserEtablissement() ;
            $user_etablissement->id_user = Yii::$app->user->identity->id ;
            $user_etablissement->id_etablissement = $this->id_etablissement ;
            $user_etablissement->save() ;
        }
    }
}