mybatis0110- SqlSession的执行过程

喜欢ヅ旅行 2023-08-17 15:23 148阅读 0赞

下面的查询过程是从MapperMethod的execute方法开始的

1. result = sqlSession.selectOne(command.getName(), param);执行DefaultSqlSession的selectOne方法；

在DefaultSqlSession中最终由selectList执行

/**
    * @statement ms的id
    * @parameter 参数
    * @rowBounds 分页参数
    */
    public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
      try {
          // mapper的一个方法和方法对应的sql
        MappedStatement ms = configuration.getMappedStatement(statement);
        // 
        return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
      } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
      } finally {
        ErrorContext.instance().reset();
      }
    }

2. executor是之前创建的有三种（SimpleExecutor,ReuseExecutor,BatchExecutor以及他们的父类BaseExecutor 还有其它暂时先不管），query方法是由BaseExecutor实现的，所以首先进入BaseExecutor的query方法

// 方法一
     public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
       BoundSql boundSql = ms.getBoundSql(parameter);
       CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
       return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
    }
    
    // 方法二
    public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
      ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
      if (closed) {
        throw new ExecutorException("Executor was closed.");
      }
      if (queryStack == 0 && ms.isFlushCacheRequired()) {
        clearLocalCache();
      }
      List<E> list;
      try {
        queryStack++;
        // 获取缓存的内容
        list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
        if (list != null) {
          handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
        } else {
            // 缓存为空从数据库中查询
          list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
        }
      } finally {
        queryStack--;
      }
      if (queryStack == 0) {
        for (DeferredLoad deferredLoad : deferredLoads) {
          deferredLoad.load();
        }
        // issue #601
        deferredLoads.clear();
        if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
          // issue #482
          clearLocalCache();
        }
      }
      return list;
    }
    
    // 方法三
    private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
      List<E> list;
      localCache.putObject(key, EXECUTION_PLACEHOLDER);
      try {
          // 从数据库中执行查询，由具体的Executor实现类实现
        list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
      } finally {
        localCache.removeObject(key);
      }
      localCache.putObject(key, list);
      if (ms.getStatementType() == StatementType.CALLABLE) {
        localOutputParameterCache.putObject(key, parameter);
      }
      return list;
    }

3. 顺序执行上述三个方法以后，会进入SimpleExecutor的doQuery方法

public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
      Statement stmt = null;
      try {
        Configuration configuration = ms.getConfiguration();
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
        stmt = prepareStatement(handler, ms.getStatementLog());
        return handler.<E>query(stmt, resultHandler);
      } finally {
        closeStatement(stmt);
      }
    }

4. 最后在SimpleStatementHandler中执行jdbc的Statement.execute真正的执行sql

public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
      String sql = boundSql.getSql();
      // jdbc的Statement指定execute方法，ibatis框架就把封装好的sql送过来了
      statement.execute(sql);
      return resultSetHandler.<E>handleResultSets(statement);
    }

5. 执行流程

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