title: Yii2 - Unable to find 'app\models\User' in file: backend/models/User.php. Namespace missing?
body: <p>I used both namespace in this file backend/models/User.php</p>
  
  <p>When I use namespace app\models; It shows Unable to find 'backend\models\User'.</p>
  
  <p>If I use namespace backend\models; It shows Unable to find 'app\models\User'</p>
  
  <pre><code>&lt;?php
  //namespace app\models;
  namespace backend\models;
  
  use Yii;
  use yii\base\NotSupportedException;
  use yii\behaviors\TimestampBehavior;
  use yii\db\ActiveRecord;
  use yii\web\IdentityInterface;
  
  
  class User extends ActiveRecord implements IdentityInterface
  {
      const STATUS_DELETED = 0;
      const STATUS_ACTIVE = 10;
      const ROLE_USER = 10;
  
      /**
       * @inheritdoc
       */
      public static function tableName()
      {
          return 'admin';
      }
  
      /**
       * @inheritdoc
       */
      public function behaviors()
      {
          return [
              TimestampBehavior::className(),
          ];
      }
  
      /**
       * @inheritdoc
       */
      public function rules()
      {
          return [
              ['status', 'default', 'value' =&gt; self::STATUS_ACTIVE],
              ['status', 'in', 'range' =&gt; [self::STATUS_ACTIVE, self::STATUS_DELETED]],
  
              ['role', 'default', 'value' =&gt; self::ROLE_USER],
              ['role', 'in', 'range' =&gt; [self::ROLE_USER]],
          ];
      }
  
      /**
       * @inheritdoc
       */
      public static function findIdentity($id)
      {
          return static::findOne(['id' =&gt; $id, 'status' =&gt; self::STATUS_ACTIVE]);
      }
  
      /**
       * @inheritdoc
       */
      public static function findIdentityByAccessToken($token, $type = null)
      {
          throw new NotSupportedException('"findIdentityByAccessToken" is not implemented.');
      }
  
      /**
       * Finds user by username
       *
       * @param string $username
       * @return static|null
       */
      public static function findByUsername($username)
      {
          return static::findOne(['username' =&gt; $username, 'status' =&gt; self::STATUS_ACTIVE]);
      }
  
      /**
       * Finds user by password reset token
       *
       * @param string $token password reset token
       * @return static|null
       */
      public static function findByPasswordResetToken($token)
      {
          if (!static::isPasswordResetTokenValid($token)) {
              return null;
          }
  
          return static::findOne([
              'password_reset_token' =&gt; $token,
              'status' =&gt; self::STATUS_ACTIVE,
          ]);
      }
  
      /**
       * Finds out if password reset token is valid
       *
       * @param string $token password reset token
       * @return boolean
       */
      public static function isPasswordResetTokenValid($token)
      {
          if (empty($token)) {
              return false;
          }
          $expire = Yii::$app-&gt;params['user.passwordResetTokenExpire'];
          $parts = explode('_', $token);
          $timestamp = (int) end($parts);
          return $timestamp + $expire &gt;= time();
      }
  
      /**
       * @inheritdoc
       */
      public function getId()
      {
          return $this-&gt;getPrimaryKey();
      }
  
      /**
       * @inheritdoc
       */
      public function getAuthKey()
      {
          return $this-&gt;auth_key;
      }
  
      /**
       * @inheritdoc
       */
      public function validateAuthKey($authKey)
      {
          return $this-&gt;getAuthKey() === $authKey;
      }
  
      /**
       * Validates password
       *
       * @param string $password password to validate
       * @return boolean if password provided is valid for current user
       */
      public function validatePassword($password)
      {
          return Yii::$app-&gt;security-&gt;validatePassword($password, $this-&gt;password_hash);
      }
  
      /**
       * Generates password hash from password and sets it to the model
       *
       * @param string $password
       */
      public function setPassword($password)
      {
          $this-&gt;password_hash = Yii::$app-&gt;security-&gt;generatePasswordHash($password);
      }
  
      /**
       * Generates "remember me" authentication key
       */
      public function generateAuthKey()
      {
          $this-&gt;auth_key = Yii::$app-&gt;security-&gt;generateRandomString();
      }
  
      /**
       * Generates new password reset token
       */
      public function generatePasswordResetToken()
      {
          $this-&gt;password_reset_token = Yii::$app-&gt;security-&gt;generateRandomString() . '_' . time();
      }
  
      /**
       * Removes password reset token
       */
      public function removePasswordResetToken()
      {
          $this-&gt;password_reset_token = null;
      }
  }
  </code></pre>