Mybatis 源码之更新数据库

流程图

https://www.processon.com/view/link/655098457b996f7b645b6afe

更新

定位: org.apache.ibatis.session.defaults.DefaultSqlSession#update

public int update(String statement, Object parameter) {
  try {
    //每次要更新之前，dirty标志设为true
    dirty = true;
    MappedStatement ms = configuration.getMappedStatement(statement);
    // 用执行器来update结果
    return executor.update(ms, wrapCollection(parameter));
  } catch (Exception e) {
    throw ExceptionFactory.wrapException("Error updating database.  Cause: " + e, e);
  } finally {
    ErrorContext.instance().reset();
  }
}

org.apache.ibatis.executor.CachingExecutor#update

public int update(MappedStatement ms, Object parameterObject) throws SQLException {  
// 刷新二级缓存完再 update
flushCacheIfRequired(ms);
return delegate.update(ms, parameterObject);  
}

org.apache.ibatis.executor.BaseExecutor#update

// SqlSession.update/insert/delete 都会调用此方法
public int update(MappedStatement ms, Object parameter) throws SQLException {
  ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId());
  // 判断当前Executor是否已经关闭
  if (closed) {
    throw new ExecutorException("Executor was closed.");
  }
  // 先清局部缓存(一级缓存)，再更新，如何更新交由子类，模板方法模式
  clearLocalCache();
  // 执行sql语句
  return doUpdate(ms, parameter);
}

org.apache.ibatis.executor.SimpleExecutor#doUpdate

public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
  Statement stmt = null;
  try {
    Configuration configuration = ms.getConfiguration();
    // 新建一个 StatementHandler
    // 这里看到 ResultHandler 传入的是 null
    StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
    // 准备语句
    stmt = prepareStatement(handler, ms.getStatementLog());
    return handler.update(stmt);
  } finally {
    closeStatement(stmt);
  }
}

org.apache.ibatis.executor.statement.PreparedStatementHandler#update

public int update(Statement statement) throws SQLException {
  PreparedStatement ps = (PreparedStatement) statement;
  // 调用 PreparedStatement.execute
  ps.execute();
  // 调用 PreparedStatement.getUpdateCount
  int rows = ps.getUpdateCount();
  // 获取实际入参
  Object parameterObject = boundSql.getParameterObject();
  // 若配置了 useGeneratedKeys 并且是 insert 语句, 
  // 则返回 Jdbc3KeyGenerator.INSTANCE, 否则返回 NoKeyGenerator.INSTANCE
  // 若配置了 sekectKey, 则使用 SelectKeyGenerator 的实例
  KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
  // 执行主键生成器的后置方法, 主要给入参设置对应的主键值
  keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);
  // 返回更新的行数
  return rows;
}

插入

org.apache.ibatis.session.defaults.DefaultSqlSession#insert

@Override
public int insert(String statement) {
  return insert(statement, null);
}
@Override
public int insert(String statement, Object parameter) {
  // 调用更新
  return update(statement, parameter);
}

PreparedStatementHandler 更新

定位: org.apache.ibatis.executor.statement.BaseStatementHandler#BaseStatementHandler

作用： 语句处理器的基类, 其子类有PreparedStatementHandler, SimpleStatementHandler, CallableStatementHandler

protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
  // 初始化字段
  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
    // 调用 KeyGenerator.processBefore方法获取主键
    generateKeys(parameterObject);
    boundSql = mappedStatement.getBoundSql(parameterObject);
  }

  this.boundSql = boundSql;
  // 生成 parameterHandler
  this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
  // 生成 resultSetHandler
  this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
}
// 生成 key
protected void generateKeys(Object parameter) {
  KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
  ErrorContext.instance().store();
  // 调用主键生成器的前置方法
  keyGenerator.processBefore(executor, mappedStatement, null, parameter);
  ErrorContext.instance().recall();
}

org.apache.ibatis.executor.keygen.Jdbc3KeyGenerator

主键生成器, 默认使用数据库的生成策略, 将生成后的主键赋值到入参对应的字段中

@Override
public void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
  // do nothing
}
@Override
public void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
  // 将用户传入的实参 parameter 封装成集合类型，然后传入 processBatch 方法中处理
  processBatch(ms, stmt, parameter);
}
public void processBatch(MappedStatement ms, Statement stmt, Object parameter) {
  // 获取 keyProperties 属性指定的属性名称，它表示主键对应的属性名称
  final String[] keyProperties = ms.getKeyProperties();
  if (keyProperties == null || keyProperties.length == 0) {
    return;
  }
  // 核心是使用 JDBC3 的 Statement.getGeneratedKeys
  try (ResultSet rs = stmt.getGeneratedKeys()) {
    // 获取ResultSet的元数据信息
    final ResultSetMetaData rsmd = rs.getMetaData();
    final Configuration configuration = ms.getConfiguration();
    // 检测数据库生成的主键的列数与 keyProperties 属性指定的列数是否匹配
    if (rsmd.getColumnCount() < keyProperties.length) {
      // Error?
    } else {
      // 主键列的值赋值到入参对象中
      assignKeys(configuration, rs, rsmd, keyProperties, parameter);
    }
  } catch (Exception e) {
    throw new ExecutorException("Error getting generated key or setting result to parameter object. Cause: " + e, e);
  }
}

删除

org.apache.ibatis.session.defaults.DefaultSqlSession#delete

@Override
public int delete(String statement) {
  return update(statement, null);
}
@Override
public int delete(String statement, Object parameter) {
  // delete 也是调用更新
  return update(statement, parameter);
}