Mybatis Insert、update、delete流程

上文mybatis源码简书我们讲到sqlsession中通过executor来执行sql，我们接着往下看

update方法点进去，我们进到baseexecutor

这里我们看到 clearLocalCache 方法，可见每次更新都会清除缓存

我们再看到doUpdate

 public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
     Statement stmt = null;
     try {
       Configuration configuration = ms.getConfiguration();
       StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
       stmt = prepareStatement(handler, ms.getStatementLog());
       return handler.update(stmt);
     } finally {
       closeStatement(stmt);
     }
   }

先看第5行，生成一个 StatementHandler，StatementHandler是mybatis4大对象之一，负责处理Mybatis与JDBC之间Statement的交互。

我们再看下newStatementHandler，

这里又看 RoutingStatementHandler，先不管，再点进去，会发现会有不同类型的StatementHandler

SimpleStatementHandler，这个很简单了，就是对应我们JDBC中常用的Statement接口，用于简单SQL的处理；
PreparedStatementHandler，这个对应JDBC中的PreparedStatement，预编译SQL的接口；
CallableStatementHandler，这个对应JDBC中CallableStatement，用于执行存储过程相关的接口；
RoutingStatementHandler，这个接口是以上三个接口的路由，没有实际操作，只是负责上面三个StatementHandler的创建及调用。

这几个StatementHandler他有共同的构造器，都在BaseStatementHandler

 protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
     this.configuration = mappedStatement.getConfiguration();
     this.executor = executor;
     this.mappedStatement = mappedStatement;
     this.rowBounds = rowBounds;

     this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
     this.objectFactory = configuration.getObjectFactory();

     if (boundSql == null) { // issue #435, get the key before calculating the statement
       generateKeys(parameterObject);
       boundSql = mappedStatement.getBoundSql(parameterObject);
     }

     this.boundSql = boundSql;

     this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
     this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
   }

这里顺便创建了parameterHandler和 resultSetHandler

parameterHandler的作用就是进行参数预编译设置，resultSetHandler封装我们得到的结果。

public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
 2     Statement stmt = null;
 3     try {
 4       Configuration configuration = ms.getConfiguration();
 5       StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
 6       stmt = prepareStatement(handler, ms.getStatementLog());
 7       return handler.update(stmt);
 8     } finally {
 9       closeStatement(stmt);
10     }
11   }

再看第六行，我们在生成StatementHandler，开始执行prepareStatement

 private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
     Statement stmt;
     Connection connection = getConnection(statementLog);
     //调用StatementHandler.prepare
     stmt = handler.prepare(connection);
     //调用StatementHandler.parameterize
     handler.parameterize(stmt);
     return stmt;
   }

我们看到prepare方法，生成statement,用过jdbc的都知道，Statement对象主要用于将 SQL 语句发送到数据库中，执行对数据库的数据的检索或者更新

生成好statement后，我们再看下第7行

public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
 2     Statement stmt = null;
 3     try {
 4       Configuration configuration = ms.getConfiguration();
 5       StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
 6       stmt = prepareStatement(handler, ms.getStatementLog());
 7       return handler.update(stmt);
 8     } finally {
 9       closeStatement(stmt);
10     }
11   }

这里就是真正的执行sql的地方。