php - Yii2:检查数据库中是否存在 ActiveRecord 模型

Question

如何检查数据库中模型的存在？在 Yii 1 版本中是这样的User::model()->exist()

Answer 1

在 Yii2 中，您可以将 exists() 添加到您的查询链中:

User::find()
    ->where( [ 'id' => 1 ] )
    ->exists(); 

(生成的 SQL 如下所示:SELECT 1 FROM `tbl_user` WHERE `id`=1。)

这里是 Query->exists()from Yii2 source :

/**
 * Returns a value indicating whether the query result contains any row of data.
 * @param Connection $db the database connection used to generate the SQL statement.
 * If this parameter is not given, the `db` application component will be used.
 * @return bool whether the query result contains any row of data.
 */
public function exists($db = null)
{
    if ($this->emulateExecution) {
        return false;
    }
    $command = $this->createCommand($db);
    $params = $command->params;
    $command->setSql($command->db->getQueryBuilder()->selectExists($command->getSql()));
    $command->bindValues($params);
    return (bool) $command->queryScalar();
}