问题描述

使用 Zend Framework，我需要 (1) 从 MySQL 数据库读取一条记录，以及 (2) 立即写回该记录以表明它已被读取.我不希望其他进程或查询能够在步骤 (1) 和 (2) 之间读取或写入同一条记录.

Using Zend Framework, I need to (1) read a record from a MySQL database, and (2) immediately write back to that record to indicate that it has been read. I don't want other processes or queries to be able to read from or write to the same record in between steps (1) and (2).

我正在考虑对这些步骤使用事务.如果我使用以下方法，是否满足我的要求?

I was considering using a transaction for these steps. If I use the following methods, will that fulfil my requirements?

Zend_Db_Adapter_Abstract::beginTransaction()
Zend_Db_Adapter_Abstract::commit()
Zend_Db_Adapter_Abstract::rollBack()

推荐答案

假设您正在使用 InnoDB 引擎，用于您将在其上发出事务的表:

Presupposing you are using the InnoDB engine for tables that you will issue transactions on:

如果要求你首先需要读取该行并独占锁定它，那么在你打算更新它之前，你应该发出一个 SELECT ... FOR UPDATE 查询.类似的东西:

If the requirement is that you first need to read the row and exclusively lock it, before you are going to update it, you should issue a SELECT ... FOR UPDATE query. Something like:

$db->beginTransaction();
try
{
    $select = $db->select()
                 ->forUpdate() // <-- here's the magic
                 ->from(
                     array( 'a' => 'yourTable' ),
                     array( 'your', 'column', 'names' )
                 )
                 ->where( 'someColumn = ?', $whatever );

    $result = $this->_adapter->fetchRow( $select );

    /*
      alter data in $result
      and update if necessary:
    */
    $db->update( 'yourTable', $result, array( 'someColumn = ?' => $whatever ) );

    $db->commit();
}
catch( Exception $e )
{
    $db->rollBack();
}

或者只是在 $db 上发出原始"SELECT ... FOR UPDATE 和 UPDATE SQL 语句.

Or simply issue 'raw' SELECT ... FOR UPDATE and UPDATE SQL statements on $db of course.

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