TransactionsAndConcurrency.md

Transactions and Concurrency

https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/transactions-and-concurrency.html

• Transaction Demarcation 事务划分
  • For the most part, Doctrine 2 already takes care of proper transaction demarcation for you: All the write operations (INSERT/UPDATE/DELETE) are queued until EntityManager#flush() is invoked which wraps all of these changes in a single transaction.
  • 在大多数情况下，Doctrine 2已经为你完成了正确的事务划分：所有写操作（INSERT / UPDATE / DELETE）都会排队，直到调用EntityManager＃flush（），它会在单个事务中包装所有这些更改。
  • Doctrine 2 also allows (and encourages) you to take over and control transaction demarcation yourself.
• Approach
  • Implicitly 隐式
    • The first approach is to use the implicit transaction handling provided by the Doctrine ORM EntityManager.
    • Since we do not do any custom transaction demarcation in the above code, EntityManager#flush() will begin and commit/rollback a transaction. This behavior is made possible by the aggregation of the DML operations by the Doctrine ORM and is sufficient if all the data manipulation that is part of a unit of work happens through the domain model and thus the ORM.
  • Explicitly 显式
    • Explicit transaction demarcation is required when you want to include custom DBAL operations in a unit of work or when you want to make use of some methods of the EntityManager API that require an active transaction. Such methods will throw a TransactionRequiredException to inform you of that requirement.

    <?php
    // $em instanceof EntityManager
    $em->getConnection()->beginTransaction(); // suspend auto-commit
    try {
        //... do some work
        $user = new User;
        $user->setName('George');
        $em->persist($user);
        $em->flush();
        $em->getConnection()->commit();
    } catch (Exception $e) {
        $em->getConnection()->rollBack();
        throw $e;
    }
    
    <?php
    // $em instanceof EntityManager
    $em->transactional(function($em) {
        //... do some work
        $user = new User;
        $user->setName('George');
        $em->persist($user);
    });

    • The difference betweenConnection#transactional($func) and EntityManager#transactional($func) is that the latter abstraction flushes the EntityManager prior to transaction commit and rolls back the transaction when an exception occurs.
• Locking Support 锁的支持
  • Optimistic Locking 乐观锁
  • Pessimistic Locking 悲观锁