Yii2 Not unique table/alias: 'user'

Question

In the "Ticket" model:

public function getUser()
{
    return $this->hasOne(User::className(), ['id' => 'user_id']);
}


public function getSupervisor()
{
    return $this->hasOne(User::className(), ['id' => 'supervisor_id']);

In the "TicketSearch" model:

    $query->joinWith(['user','supervisor']);

    $query
        ->andFilterWhere(['like', 'user.surname', $this->user_id])
        ->andFilterWhere(['like', 'user.surname', $this->supervisor_id]

If I try to search supervisor, get this error:

Not unique table/alias: 'user'
The SQL being executed was: SELECT COUNT(*) FROM `ticket` LEFT JOIN `user` ON `ticket`.`user_id` = `user`.`id` LEFT JOIN `user` ON `ticket`.`supervisor_id` = `user`.`id` WHERE `user`.`surname` LIKE '%surname4%'

I have tried to change name user table:

    public function getSupervisor()
    {
        return $this->hasOne(User::className(), ['id' => 'supervisor_id'])
->from(User::tableName() . 'u2');
    }

But this error returned:

You have an error in your SQL syntax; check the manual that corresponds 
to your MySQL server version for the right syntax to use near 'u2.`id` 
WHERE `supervisor`.`surname` LIKE '%surname4%'' at line 1 The SQL being executed was:
SELECT COUNT(*) FROM `ticket` LEFT JOIN `user` ON `ticket`.`user_id` = `user`.`id` LEFT JOIN `user`u2 ON
`ticket`.`supervisor_id` = `user`u2.`id` WHERE `supervisor`.`surname` LIKE '%surname4%'

Answer 1

You missed space before alias. Should be:

public function getSupervisor()
{
    return $this->hasOne(User::className(), ['id' => 'supervisor_id'])
        ->from(User::tableName() . ' u2');
}

You can also specify it as array key:

public function getSupervisor()
{
    return $this->hasOne(User::className(), ['id' => 'supervisor_id'])
        ->from(['u2' => User::tableName()]);
}

Or even in joinWith() with this relation:

->joinWith([
    'supervisor' => function ($query) {
        /* @var $query \yii\db\ActiveQuery */

        $query->from(User::tableName() . ' u2');
        // or $query->from(['u2' => User::tableName()]);
    },
]);

Official documentation:

• from()

Answer 2

Since version 2.0.7 there is alias() method:

public function getSupervisor()
{
    return $this->hasOne(User::className(), ['id' => 'supervisor_id'])->alias('supervisor');
}