生成内存数据库的事务ID
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在撰写本文时，TRANSACTION_ID（）不支持内存数据库。我可以使用序列表生成自己的ID，但尚不清楚如何将现有ID与触发器进行通信。第一个触发器应生成一个新的ID。后续触发器（在同一事务中）应共享现有ID。
我可以使用线程局部变量来共享现有的ID，但这似乎很脆弱。有一个更好的方法吗？
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肉簧咸缮
事务中的第一个操作设置会话变量，如下所示：该事务中的其他操作使用会话变量：妒垮
/** * Invoked when a transaction completes. */ public abstract class TransactionListener extends Value { private boolean invoked; /** * Invoked when the transaction completes. */ protected abstract void onCompleted(); @Override public String getSQL() { return null; } @Override public int getType() { throw new AssertionError(\"Unexpected method invocation\"); } @Override public long getPrecision() { throw new AssertionError(\"Unexpected method invocation\"); } @Override public int getDisplaySize() { throw new AssertionError(\"Unexpected method invocation\"); } @Override public String getString() { throw new AssertionError(\"Unexpected method invocation\"); } @Override public Object getObject() { throw new AssertionError(\"Unexpected method invocation\"); } @Override public void set(PreparedStatement prep, int parameterIndex) throws SQLException { throw new AssertionError(\"Unexpected method invocation\"); } @Override protected int compareSecure(Value v, CompareMode mode) { throw new AssertionError(\"Unexpected method invocation\"); } @Override public int hashCode() { throw new AssertionError(\"Unexpected method invocation\"); } @Override public boolean equals(Object other) { throw new AssertionError(\"Unexpected method invocation\"); } @Override public boolean isLinked() { return !invoked; } @Override public void close() { invoked = true; onCompleted(); } } // -------------TRIGGER BELOW----------- public void fire(final Connection connection, ResultSet oldRow, ResultSet newRow) throws SQLException { Statement statement = connection.createStatement(); long transactionId; ResultSet rs = statement.executeQuery(\"SELECT @TRANSACTION_ID\"); try { rs.next(); transactionId = rs.getLong(1); if (transactionId == 0) { // Generate a new transaction id rs.close(); JdbcConnection jdbcConnection = (JdbcConnection) connection; final Session session = (Session) jdbcConnection.getSession(); session.unlinkAtCommit(new TransactionListener() { @Override protected void onCompleted() { boolean oldAutoCommit = session.getAutoCommit(); session.setAutoCommit(false); try { Statement statement = connection.createStatement(); statement.executeQuery(\"SELECT SET(@TRANSACTION_ID, NULL)\"); statement.close(); } catch (SQLException e) { throw new AssertionError(e); } finally { session.setAutoCommit(oldAutoCommit); } } }); rs = statement.executeQuery(\"SELECT SET(@TRANSACTION_ID, \" + \"audit_transaction_sequence.NEXTVAL)\"); rs.next(); transactionId = rs.getLong(1); } } finally { rs.close(); } assert (transactionId != 0); // ... }为null，则注册一个新的事件侦听器并递增顺序。 如果不为空，则从中获取当前的交易ID。 此解决方法的两个主要问题是： 它非常脆弱。如果Session.unlinkAtCommit（）将来更改，则可能会中断事件侦听器。 为了检索交易ID，我们必须在每个触发器的顶部重复很多样板代码。 将其实现为内置函数TRANSACTION_LOCAL_ID（）会容易得多。此功能将返回类似于HSQLDB的特定于数据库实例的事务ID。