PHP PDO MySQL 以及它如何真正处理 MySQL 事务？

Posted 2023-03-14

技术标签:

【中文标题】PHP PDO MySQL 以及它如何真正处理 MySQL 事务？【英文标题】：PHP PDO MySQL and how does it really deal with MySQL transactions? 【发布时间】：2018-05-28 08:26:29 【问题描述】：

我正在努力克服它，但我就是无法理解在 php 中使用 PDO 和 mysql 进行事务处理背后的逻辑。

我知道这个问题会很长，但我认为这是值得的。

鉴于我阅读了很多关于 MySQL 事务、服务器如何处理它们、它们如何与锁和其他隐式提交语句等相关的内容，不仅在 SO 上，而且在 MySQL 和 PHP 手册上也有：

Mysql transactions within transactions Difference between SET autocommit=1 and START TRANSACTION in mysql (Have I missed something?) https://dev.mysql.com/doc/refman/5.7/en/commit.html https://dev.mysql.com/doc/refman/5.7/en/lock-tables-and-transactions.html http://php.net/manual/en/pdo.transactions.php http://php.net/manual/en/pdo.begintransaction.php

并给出以下代码：

架构：

CREATE TABLE table_name (
  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  table_col VARCHAR(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

CREATE TABLE `another_table` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `another_col` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

test1.php（带有PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)）：

<?php

// PDO
define('DB_HOST', 'localhost');
define('DB_USER', 'user');
define('DB_PASS', 'password');
define('DB_NAME', 'db_name');

/**
 * Uses `$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);`
 */
class Database 

    private $host = DB_HOST;
    private $user = DB_USER;
    private $pass = DB_PASS;
    private $dbname = DB_NAME;

    private $pdo;

    public $error;

    private $stmt;


    public function __construct($host=NULL,$user=NULL,$pass=NULL,$dbname=NULL) 

        if ($host!==NULL)
            $this->host=$host;

        if ($user!==NULL)
            $this->user=$user;

        if ($pass!==NULL)
            $this->pass=$pass;

        if ($dbname!==NULL)
            $this->dbname=$dbname;

        // Set DSN
        $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;

        // Set options
        $options = array(
            PDO::ATTR_PERSISTENT    => false,
            PDO::ATTR_ERRMODE       => PDO::ERRMODE_EXCEPTION
        );

        // Create a new PDO instanace
        $this->pdo = new PDO($dsn, $this->user, $this->pass, $options);
        $this->pdo->exec("SET NAMES 'utf8'");

    

    public function cursorClose() 
        $this->stmt->closeCursor();
    

    public function close() 
        $this->pdo = null;
        $this->stmt = null;
        return true;
    

    public function beginTransaction() 
        $this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);
        return $this->pdo->beginTransaction();
    

    public function commit() 
        $ok = $this->pdo->commit();
        $this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    

    public function rollback() 
        $ok = $this->pdo->rollback();
        $this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    

    public function bind($param, $value, $type = null)
        if (is_null($type)) 
            switch (true) 
                case is_int($value):
                    $type = PDO::PARAM_INT;
                    break;
                case is_bool($value):
                    $type = PDO::PARAM_BOOL;
                    break;
                case is_null($value):
                    $type = PDO::PARAM_NULL;
                    break;
                default:
                    $type = PDO::PARAM_STR;
            
        
        $this->stmt->bindValue($param, $value, $type);
    

    public function runquery() 
        $this->stmt->execute();
    

    public function execute($nameValuePairArray = NULL) 
        try    
            if (is_array($nameValuePairArray) && !empty($nameValuePairArray)) 
                return $this->stmt->execute($nameValuePairArray);
            else
                return $this->stmt->execute();
         
        catch(PDOException $e) 
            $this->error = $e->getMessage();
           
        return FALSE;
    

    public function lastInsertId() 
        return $this->pdo->lastInsertId();
    

    public function insert($table, $data) 

        if (!empty($data))

            $fields = "";

            $values = "";

            foreach($data as $field => $value) 

                if ($fields=="")
                    $fields = "$field";
                    $values = ":$field";
                
                else 
                    $fields .= ",$field";
                    $values .= ",:$field";
                
            

            $query = "INSERT INTO $table ($fields) VALUES ($values) ";

            $this->query($query);

            foreach($data as $field => $value)
                $this->bind(":$field",$value);
            

            if ($this->execute()===FALSE)
                return FALSE;
            else
                return $this->lastInsertId();   
        

        $this->error = "No fields during insert";

        return FALSE;
    

    public function query($query) 
        $this->stmt = $this->pdo->prepare($query);
    

    public function setBuffered($isBuffered=false)
        $this->pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, $isBuffered);
    

    public function lockTables($tables)
        $query = "LOCK TABLES ";
        foreach($tables as $table=>$lockType)
            $query .= "$table $lockType, ";
        
        $query = substr($query,0, strlen($query)-2);
        $this->query($query);
        return $this->execute();
    

    public function unlockTables()
        $query = "UNLOCK TABLES";
        $this->query($query);
        return $this->execute();
    


$db = NULL;
try 
    $db = new Database();
    $db->beginTransaction();

    // If I call `LOCK TABLES` here... No implicit commit. Why?
    // Does `$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);` prevent it?
    $db->lockTables(array('another_table' => 'WRITE'));

    $db->insert('another_table', array('another_col' => 'TEST1_ANOTHER_TABLE'));

    $db->unlockTables();


    // If I insert a row, other MySQL clients do not see it. Why?
    // I called `LOCK TABLES` above and as the MySQL manual says:
    // 
    //      LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.
    //
    $db->insert('table_name', array('table_col' => 'TEST1_TABLE_NAME'));

    //...
    // If I rollback for some reason, everything rolls back, but shouldn't the transaction
    // be already committed with the initial `LOCK TABLES`?
    // So I should expect to get a PDOException like "There's no active transaction" or something similar, shouldn't I?
    //$db->rollback();

    // If I commit instead of the above `$db->rollback()` line, everything is committed, but only now other clients see the new row in `table_name`,
    // not straightforward as soon I called `$db->insert()`, whereas I guess they should have seen the change
    // even before the following line because I am using `LOCK TABLES` before (see `test2.php`).
    $db->commit();

catch (PDOException $e) 
    echo $e->getMessage();


if (!is_null($db)) 
    $db->close();

test2.php（没有PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0) 行的数据库（已注释掉））：

<?php

// PDO
define('DB_HOST', 'localhost');
define('DB_USER', 'user');
define('DB_PASS', 'password');
define('DB_NAME', 'db_name');

/**
 * Does not use `$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);`
 */
class Database 

    private $host = DB_HOST;
    private $user = DB_USER;
    private $pass = DB_PASS;
    private $dbname = DB_NAME;

    private $pdo;

    public $error;

    private $stmt;


    public function __construct($host=NULL,$user=NULL,$pass=NULL,$dbname=NULL) 

        if ($host!==NULL)
            $this->host=$host;

        if ($user!==NULL)
            $this->user=$user;

        if ($pass!==NULL)
            $this->pass=$pass;

        if ($dbname!==NULL)
            $this->dbname=$dbname;

        // Set DSN
        $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;

        // Set options
        $options = array(
            PDO::ATTR_PERSISTENT    => false,
            PDO::ATTR_ERRMODE       => PDO::ERRMODE_EXCEPTION
        );

        // Create a new PDO instanace
        $this->pdo = new PDO($dsn, $this->user, $this->pass, $options);
        $this->pdo->exec("SET NAMES 'utf8'");

    

    public function cursorClose() 
        $this->stmt->closeCursor();
    

    public function close() 
        $this->pdo = null;
        $this->stmt = null;
        return true;
    

    public function beginTransaction() 
        //$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);
        return $this->pdo->beginTransaction();
    

    public function commit() 
        $ok = $this->pdo->commit();
        //$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    

    public function rollback() 
        $ok = $this->pdo->rollback();
        //$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    

    public function bind($param, $value, $type = null)
        if (is_null($type)) 
            switch (true) 
                case is_int($value):
                    $type = PDO::PARAM_INT;
                    break;
                case is_bool($value):
                    $type = PDO::PARAM_BOOL;
                    break;
                case is_null($value):
                    $type = PDO::PARAM_NULL;
                    break;
                default:
                    $type = PDO::PARAM_STR;
            
        
        $this->stmt->bindValue($param, $value, $type);
    

    public function runquery() 
        $this->stmt->execute();
    

    public function execute($nameValuePairArray = NULL) 
        try    
            if (is_array($nameValuePairArray) && !empty($nameValuePairArray)) 
                return $this->stmt->execute($nameValuePairArray);
            else
                return $this->stmt->execute();
         
        catch(PDOException $e) 
            $this->error = $e->getMessage();
           
        return FALSE;
    

    public function lastInsertId() 
        return $this->pdo->lastInsertId();
    

    public function insert($table, $data) 

        if (!empty($data))

            $fields = "";

            $values = "";

            foreach($data as $field => $value) 

                if ($fields=="")
                    $fields = "$field";
                    $values = ":$field";
                
                else 
                    $fields .= ",$field";
                    $values .= ",:$field";
                
            

            $query = "INSERT INTO $table ($fields) VALUES ($values) ";

            $this->query($query);

            foreach($data as $field => $value)
                $this->bind(":$field",$value);
            

            if ($this->execute()===FALSE)
                return FALSE;
            else
                return $this->lastInsertId();   
        

        $this->error = "No fields during insert";

        return FALSE;
    

    public function query($query) 
        $this->stmt = $this->pdo->prepare($query);
    

    public function setBuffered($isBuffered=false)
        $this->pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, $isBuffered);
    

    public function lockTables($tables)
        $query = "LOCK TABLES ";
        foreach($tables as $table=>$lockType)
            $query .= "$table $lockType, ";
        
        $query = substr($query,0, strlen($query)-2);
        $this->query($query);
        return $this->execute();
    

    public function unlockTables()
        $query = "UNLOCK TABLES";
        $this->query($query);
        return $this->execute();
    


$db = NULL;
try 
    $db = new Database();
    $db->beginTransaction();

    // If I call `LOCK TABLES` here... There's an implicit commit.
    $db->lockTables(array('another_table' => 'WRITE'));

    $db->insert('another_table', array('another_col' => 'TEST2_ANOTHER_TABLE'));

    $db->unlockTables();


    // If I insert a row, other MySQL clients see it straightforward (no need to reach `$db->commit()`).
    // This is coherent with the MySQL manual:
    // 
    //      LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.
    //
    $db->insert('table_name', array('table_col' => 'TEST2_TABLE_NAME'));

    //...
    // If I rollback for some reason, the row does not rollback, as the transaction
    // was already committed with the initial `LOCK TABLES` statement above.
    // 
    // I cannot rollback the insert into table `table_name`
    // 
    // So I should expect to get a PDOException like "There's no active transaction" or something similar, shouldn't I?
    $db->rollback();

    // If I commit instead of the above `$db->rollback()` line, I guess nothing happens, because the transaction
    // was already committed and as I said above, and clients already saw the changes before this line was reached.
    // Again, this is coherent with the MySQL statement:
    //
    //       LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.
    //
    //$db->commit();

catch (PDOException $e) 
    echo $e->getMessage();


if (!is_null($db)) 
    $db->close();

我还有以下疑惑和未解决的问题：

使用InnoDB，有区别吗 PDO::beginTransaction() 和 PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0) 当我们在 PHP 和/或 MySQL 中使用 PDO 时使用纯 MySQL 语句 SET AUTOCOMMIT = 0; 和 START TRANSACTION;？如果是，那是什么？

如果您查看我的 PHP 示例，在 Database::beginTransaction() 包装器方法中，我在文件 test1.php 中同时使用 PDO::beginTransaction() 和 PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)，并且在文件 中不使用 PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0) >test2.php。我发现当我使用PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)时会发生奇怪的事情：

在Database (test1.php) 中有PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0) 行，在一个带有LOCK TABLES 语句的事务，LOCK TABLES 不似乎隐式提交事务，因为如果我连接对于另一个客户端，在代码到达$db->commit(); 行之前，我看不到插入的行，而 MySQL 手册说：

LOCK TABLES 不是事务安全的，它会在尝试锁定表之前隐式提交任何活动事务。

因此我们可以这样说PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)（在 MySQL 上是 SET AUTOCOMMIT = 0;) 事务没有被隐式提交像LOCK TABLES这样的陈述？然后我会说有一个 MySQL手册与PHP PDO实现不一致（我不是在抱怨，我只是想了解）；

如果Database (test2.php) 中没有 PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0) 行，代码的行为似乎与 MySQL 的一致手动LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.：一旦到达LOCK TABLES查询，就会有一个隐式提交，所以在$db->insert('table_name', array('table_col' => 'TEST2_TABLE_NAME'));行之后，其他客户端甚至可以在到达$db->commit();之前看到新插入的行；

我刚才描述的以下行为的解释是什么？当我们使用 PHP 的 PDO 并在我们的事务中包含 implicit-commit 语句时，事务如何工作？

我的PHP版本是7.0.22，MySQL版本是5.7.20。

感谢您的关注。

【问题讨论】：

***.com/questions/3106737/… 看起来内容丰富。根据 PDO::beginTransaction 实际上是关闭自动提交而不是开始新事务。这种说法似乎与这种行为一致但是有什么区别呢？如果PDO::beginTransaction关闭了自动提交，那为什么我写的2个脚本的结果根据我是否使用$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);而不同呢？ 【参考方案1】：

https://dev.mysql.com/doc/refman/5.7/en/innodb-autocommit-commit-rollback.html 说：

如果在 SET autocommit = 0 的会话中禁用自动提交模式，则该会话始终打开一个事务。 COMMIT 或 ROLLBACK 语句结束当前事务并开始新事务。

因此，当您在会话中设置 autocommit=0（称为会话 1）时，这会隐式打开一个事务，并使其无限期地保持打开状态。

默认事务隔离级别是 REPEATABLE-READ。因此，在会话 1 明确提交或回滚之前，您的会话将不会看到来自其他会话工作的已提交更改的刷新视图。

您在另一个会话 2 中的 LOCK TABLES 确实会导致隐式提交，但会话 1 看不到结果，因为由于它自己的事务，它仍然只能看到数据的隔离视图快照。

【讨论】：

感谢您的回复。在我的情况下，会话 1 是设置 autocommit = 0 并使用 LOCK TABLES（不是会话 2）的会话。在这种情况下session 2 会发生什么？会话 1 中 LOCK 之前的所有内容都将被提交，另一个事务直接开始，但会话 2 直到有明确的 COMMIT/ROLLBACK 语句才能看到更改？ @tonix，我建议你打开两个终端窗口并在每个窗口中运行mysql 客户端。然后你可以轻松地做一些实验。我按照你说的做了，似乎当AUTOCOMMIT=0 时，你的声明A COMMIT or ROLLBACK statement ends the current transaction and a new one starts. 也适用于像LOCK TABLES 这样的隐式提交声明。对吗？是的，应该是正确的。当 autocommit=0 时，您始终有一个事务处于打开状态，这意味着一旦提交了一个事务，就会开始一个新事务。所以如果你COMMIT、ROLLBACK或者发出像LOCK TABLES这样的隐式提交语句，MySQL就会自动为你执行START TRANSACTION，对吧？

以上是关于PHP PDO MySQL 以及它如何真正处理 MySQL 事务？的主要内容，如果未能解决你的问题，请参考以下文章

PHP操作PDO预处理以及事务

php PDO 和 mysql：如何插入地理点类型？

PDO操作MYSQL基础教程分享

如何在PHP下开启PDO MySQL的扩展