项目开发-iBatis事务源码之SQL执行

接上篇，在开启事务后，执行SQL语句，整理SQL执行流程如下，以插入为例。

SqlMapClientImpl的insert

  public Object insert(String id, Object param) throws SQLException {
    return getLocalSqlMapSession().insert(id, param);
  }

SqlMapSessionImpl的insert

  public Object insert(String id, Object param) throws SQLException {
    return delegate.insert(sessionScope, id, param);
  }

SqlMapExecutorDelegate的insert

 /**
   * Call an insert statement by ID
   *
   * @param sessionScope - the session
   * @param id      - the statement ID
   * @param param   - the parameter object
   * @return - the generated key (or null)
   * @throws SQLException - if the insert fails
   */
  public Object insert(SessionScope sessionScope, String id, Object param) throws SQLException {
    Object generatedKey = null;

    MappedStatement ms = getMappedStatement(id);
    Transaction trans = getTransaction(sessionScope);
    boolean autoStart = trans == null;

    try {
      trans = autoStartTransaction(sessionScope, autoStart, trans);

      SelectKeyStatement selectKeyStatement = null;
      if (ms instanceof InsertStatement) {
        selectKeyStatement = ((InsertStatement) ms).getSelectKeyStatement();
      }

      // Here we get the old value for the key property. We'll want it later if for some reason the
      // insert fails.
      Object oldKeyValue = null;
      String keyProperty = null;
      boolean resetKeyValueOnFailure = false;
      if (selectKeyStatement != null && !selectKeyStatement.isRunAfterSQL()) {
        keyProperty = selectKeyStatement.getKeyProperty();
        oldKeyValue = PROBE.getObject(param, keyProperty);
        generatedKey = executeSelectKey(sessionScope, trans, ms, param);
        resetKeyValueOnFailure = true;
      }

      StatementScope statementScope = beginStatementScope(sessionScope, ms);
      try {
        ms.executeUpdate(statementScope, trans, param);
      }catch (SQLException e){
        // uh-oh, the insert failed, so if we set the reset flag earlier, we'll put the old value
        // back...
        if(resetKeyValueOnFailure) PROBE.setObject(param, keyProperty, oldKeyValue);
        // ...and still throw the exception.
        throw e;
      } finally {
        endStatementScope(statementScope);
      }

      if (selectKeyStatement != null && selectKeyStatement.isRunAfterSQL()) {
        generatedKey = executeSelectKey(sessionScope, trans, ms, param);
      }

      autoCommitTransaction(sessionScope, autoStart);
    } finally {
      autoEndTransaction(sessionScope, autoStart);
    }

    return generatedKey;
  }

添加操作会获取当前SessionScope的事务信息，如果没有事务，则添加一个默认事务，完成插入操作的自动提交

MappedStatement的executeUpdate方法

  public int executeUpdate(StatementScope statementScope, Transaction trans, Object parameterObject)
      throws SQLException {
    ErrorContext errorContext = statementScope.getErrorContext();
    errorContext.setActivity("preparing the mapped statement for execution");
    errorContext.setObjectId(this.getId());
    errorContext.setResource(this.getResource());

    statementScope.getSession().setCommitRequired(true);

    try {
      parameterObject = validateParameter(parameterObject);

      Sql sql = getSql();

      errorContext.setMoreInfo("Check the parameter map.");
      ParameterMap parameterMap = sql.getParameterMap(statementScope, parameterObject);

      errorContext.setMoreInfo("Check the result map.");
      ResultMap resultMap = sql.getResultMap(statementScope, parameterObject);

      statementScope.setResultMap(resultMap);
      statementScope.setParameterMap(parameterMap);

      int rows = 0;

      errorContext.setMoreInfo("Check the parameter map.");
      Object[] parameters = parameterMap.getParameterObjectValues(statementScope, parameterObject);

      errorContext.setMoreInfo("Check the SQL statement.");
      String sqlString = sql.getSql(statementScope, parameterObject);

      errorContext.setActivity("executing mapped statement");
      errorContext.setMoreInfo("Check the statement or the result map.");
      rows = sqlExecuteUpdate(statementScope, trans.getConnection(), sqlString, parameters);

      errorContext.setMoreInfo("Check the output parameters.");
      if (parameterObject != null) {
        postProcessParameterObject(statementScope, parameterObject, parameters);
      }

      errorContext.reset();
      sql.cleanup(statementScope);
      notifyListeners();
      return rows;
    } catch (SQLException e) {
      errorContext.setCause(e);
      throw new NestedSQLException(errorContext.toString(), e.getSQLState(), e.getErrorCode(), e);
    } catch (Exception e) {
      errorContext.setCause(e);
      throw new NestedSQLException(errorContext.toString(), e);
    }
  }

iBatis的增、删、改三种操作的SQL的最终都是调用MappedStatement的executeUpdate是执行，这三种操作都需要提交事务。所以操作执行时会设置SessionScope的事务提交标识为真。流程与insert类似，只是少了selectKey标签的处理。