正文
Mybatis Insert、update、delete流程
小程序：扫一扫查出行【扫一扫了解最新限行尾号】
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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。
