Object caching in Yii2. An example that results in an error. Why?

Question

Yii

Faced a problem. There is a function that gets the id of the dialog with the user by his id (user):

public static function getDialogByUserId(int $user_id)
  {
    $keyCache = 'dlg:byuserid:' . $user_id;
    $unionQuery = Yii::$app->redis->get($keyCache);
    
    if (false === $unionQuery) {
      $query1 = self::find()
            ->where(['user_one' => $user_id, 'user_two' => Yii::$app->user->id]);
  
      $query2 = self::find()
            ->where(['user_two' => $user_id, 'user_one' => Yii::$app->user->id]);
  
      $unionQuery = self::find()
        ->from(['x' => $query1->union($query2)])
        ->one();
echo '<pre>';
var_dump($unionQuery);
echo '</pre>';
      //Yii::$app->redis->set($keyCache, $unionQuery, 600);
    }

    return $unionQuery;
  }

radish is not native to yii, but pkhpshnaya is used as a cache.
In this form, it works fine, i.e. the dialogue is searched, the AR object is returned. But if I try to shove this object into a radish, then an error about the lack of memory takes off. Why?
AR object dump:

object(common\models\dialogs\Conversation)#157 (8) {
  ["_attributes":"yii\db\BaseActiveRecord":private]=>
  array(7) {
    ["c_id"]=>
    int(48)
    ["user_one"]=>
    int(8)
    ["user_two"]=>
    int(3)
    ["last_message"]=>
    string(37) "Ну да, типа работает "
    ["ip"]=>
    string(15) "255.255.255.255"
    ["created_at"]=>
    string(19) "2016-07-23 04:05:51"
    ["updated_at"]=>
    string(19) "2016-07-23 04:30:23"
  }
  ["_oldAttributes":"yii\db\BaseActiveRecord":private]=>
  array(7) {
    ["c_id"]=>
    int(48)
    ["user_one"]=>
    int(8)
    ["user_two"]=>
    int(3)
    ["last_message"]=>
    string(37) "Ну да, типа работает "
    ["ip"]=>
    string(15) "255.255.255.255"
    ["created_at"]=>
    string(19) "2016-07-23 04:05:51"
    ["updated_at"]=>
    string(19) "2016-07-23 04:30:23"
  }
  ["_related":"yii\db\BaseActiveRecord":private]=>
  array(0) {
  }
  ["_errors":"yii\base\Model":private]=>
  NULL
  ["_validators":"yii\base\Model":private]=>
  NULL
  ["_scenario":"yii\base\Model":private]=>
  string(7) "default"
  ["_events":"yii\base\Component":private]=>
  array(2) {
    ["beforeInsert"]=>
    array(1) {
      [0]=>
      array(2) {
        [0]=>
        array(2) {
          [0]=>
          object(yii\behaviors\TimestampBehavior)#159 (6) {
            ["createdAtAttribute"]=>
            string(10) "created_at"
            ["updatedAtAttribute"]=>
            string(10) "updated_at"
            ["value"]=>
            object(Closure)#158 (2) {
              ["this"]=>
              *RECURSION*
              ["parameter"]=>
              array(1) {
                ["$event"]=>
                string(10) ""
              }
            }
            ["attributes"]=>
            array(2) {
              ["beforeInsert"]=>
              array(2) {
                [0]=>
                string(10) "created_at"
                [1]=>
                string(10) "updated_at"
              }
              ["beforeUpdate"]=>
              array(1) {
                [0]=>
                string(10) "updated_at"
              }
            }
            ["skipUpdateOnClean"]=>
            bool(true)
            ["owner"]=>
            *RECURSION*
          }
          [1]=>
          string(18) "evaluateAttributes"
        }
        [1]=>
        NULL
      }
    }
    ["beforeUpdate"]=>
    array(1) {
      [0]=>
      array(2) {
        [0]=>
        array(2) {
          [0]=>
          object(yii\behaviors\TimestampBehavior)#159 (6) {
            ["createdAtAttribute"]=>
            string(10) "created_at"
            ["updatedAtAttribute"]=>
            string(10) "updated_at"
            ["value"]=>
            object(Closure)#158 (2) {
              ["this"]=>
              *RECURSION*
              ["parameter"]=>
              array(1) {
                ["$event"]=>
                string(10) ""
              }
            }
            ["attributes"]=>
            array(2) {
              ["beforeInsert"]=>
              array(2) {
                [0]=>
                string(10) "created_at"
                [1]=>
                string(10) "updated_at"
              }
              ["beforeUpdate"]=>
              array(1) {
                [0]=>
                string(10) "updated_at"
              }
            }
            ["skipUpdateOnClean"]=>
            bool(true)
            ["owner"]=>
            *RECURSION*
          }
          [1]=>
          string(18) "evaluateAttributes"
        }
        [1]=>
        NULL
      }
    }
  }
  ["_behaviors":"yii\base\Component":private]=>
  array(1) {
    ["timestamp"]=>
    object(yii\behaviors\TimestampBehavior)#159 (6) {
      ["createdAtAttribute"]=>
      string(10) "created_at"
      ["updatedAtAttribute"]=>
      string(10) "updated_at"
      ["value"]=>
      object(Closure)#158 (2) {
        ["this"]=>
        *RECURSION*
        ["parameter"]=>
        array(1) {
          ["$event"]=>
          string(10) ""
        }
      }
      ["attributes"]=>
      array(2) {
        ["beforeInsert"]=>
        array(2) {
          [0]=>
          string(10) "created_at"
          [1]=>
          string(10) "updated_at"
        }
        ["beforeUpdate"]=>
        array(1) {
          [0]=>
          string(10) "updated_at"
        }
      }
      ["skipUpdateOnClean"]=>
      bool(true)
      ["owner"]=>
      *RECURSION*
    }
  }
}

Well, the error itself:

Allowed memory size of 134217728 bytes exhausted (tried to allocate 2118167486 bytes)

Answer 1

1. You receive an object. Everything is fine and there is enough memory as long as it is a standard object, but when you put it anywhere, it is apparently converted to a string. Therefore, there may not be enough memory.
2. For query caching, yii2 has a separate mechanism: www.yiiframework.com/doc-2.0/guide-caching-data.ht...

Answer 2

Forgive me, but you have a problem understanding the meaning of caching. Now you are fetching data from the database (a lot of data) and putting it in the cache. What for???? You are not using the cache effectively. In the cache, you need to put not raw data, but already processed ones. The more stages you combine, the more efficient caching is.