ResultHandler 参数映射核心逻辑-5
一、KeyGenerator
- 处理insert语句的时候，并不会自动返回生成的主键内容，而只会返回插入记录的条数。如果插入记录是自增主键希望返回实际内容的时候，可以使用KeyGenerator接口
public interface KeyGenerator {
//insert SQL执行前执行
void processBefore(Executor executor, MappedStatement ms, Statement stmt, Object parameter);
//insert SQL执行后执行
void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter);
}
-
KeyGenerator接口有三个实现类：NoKeyGenerator、Jdbc3KeyGenerator/SelectKeyGenerator
-
NoKeyGenerator:processBefore/processAfter两个方法不带任何实现
- Jdbc3KeyGenerator： 用于取回数据库生成的自增id，对应于mybatis-config.xml中的全局配置，SQL节点的useGeneratedKeys 属性
- processBefore无实现，processAfter实现自增主键id的获取
1.Jdbc3KeyGenerator
- 用于取回数据库生成的自增id，对应mybatis-config.xml配置文件中的useGeneratedKeys 全局配置，以及映射映射配置文件中SQL节点的useGeneratedKeys属性
- processBefore方法为空，processAfter方法为实现主体,直接调用processBatch批量处理结果集
public void processBatch(MappedStatement ms, Statement stmt, Object parameter) {
// keyProperties 中存储主键名称和属性名映射
final String[] keyProperties = ms.getKeyProperties();
if (keyProperties == null || keyProperties.length == 0) {
return;
}
//获取数据库生成主键
try (ResultSet rs = stmt.getGeneratedKeys()) {
//获取result元信息
final ResultSetMetaData rsmd = rs.getMetaData();
final Configuration configuration = ms.getConfiguration();
//判断数据库主键列数与 keyProperties 中的是否一致
if (rsmd.getColumnCount() < keyProperties.length) {
// Error?
} else {
//将生成主键设置到用户传入参数的位置
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);
}
}
private void assignKeys(Configuration configuration, ResultSet rs, ResultSetMetaData rsmd, String[] keyProperties,
Object parameter) throws SQLException {
if (parameter instanceof ParamMap || parameter instanceof StrictMap) {
// Multi-param or single param with @Param Map属性 参数
assignKeysToParamMap(configuration, rs, rsmd, keyProperties, (Map<String, ?>) parameter);
} else if (parameter instanceof ArrayList && !((ArrayList<?>) parameter).isEmpty()
&& ((ArrayList<?>) parameter).get(0) instanceof ParamMap) {
// Multi-param or single param with @Param in batch operation list属性参数
assignKeysToParamMapList(configuration, rs, rsmd, keyProperties, (ArrayList<ParamMap<?>>) parameter);
} else {
// Single param without @Param 普通对象参数
assignKeysToParam(configuration, rs, rsmd, keyProperties, parameter);
}
}
2.SelectKeyGenerator
- 对于不支持主键自动自增的，可以使用
标签生成主键，需要设置主键生成的SQL，需要表明SQL执行前执行还是执行后执行，都是调用processGeneratedKeys方法实现
private void processGeneratedKeys(Executor executor, MappedStatement ms, Object parameter) {
try {
if (parameter != null && keyStatement != null && keyStatement.getKeyProperties() != null) {
String[] keyProperties = keyStatement.getKeyProperties();
final Configuration configuration = ms.getConfiguration();
final MetaObject metaParam = configuration.newMetaObject(parameter);
// Do not close keyExecutor.
// The transaction will be closed by parent executor.
Executor keyExecutor = configuration.newExecutor(executor.getTransaction(), ExecutorType.SIMPLE);
//主键查询SQL
List<Object> values = keyExecutor.query(keyStatement, parameter, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER);
if (values.size() == 0) {
//主键SQL没有返回值
throw new ExecutorException("SelectKey returned no data.");
} else if (values.size() > 1) {
//主键SQL返回值有多个
throw new ExecutorException("SelectKey returned more than one value.");
} else {
//主键SQL返回值有一个
MetaObject metaResult = configuration.newMetaObject(values.get(0));
if (keyProperties.length == 1) {
//主键参数有一个
if (metaResult.hasGetter(keyProperties[0])) {
//有getter ,映射值
setValue(metaParam, keyProperties[0], metaResult.getValue(keyProperties[0]));
} else {
// no getter for the property - maybe just a single value object
// so try that
setValue(metaParam, keyProperties[0], values.get(0));
}
} else {
//多个值的主键
handleMultipleProperties(keyProperties, metaParam, metaResult);
}
}
}
} catch (ExecutorException e) {
throw e;
} catch (Exception e) {
throw new ExecutorException("Error selecting key or setting result to parameter object. Cause: " + e, e);
}
}
private void handleMultipleProperties(String[] keyProperties,
MetaObject metaParam, MetaObject metaResult) {
String[] keyColumns = keyStatement.getKeyColumns();
if (keyColumns == null || keyColumns.length == 0) {
// no key columns specified, just use the property names
//没有指定主键，则通过字段名称来设置值
for (String keyProperty : keyProperties) {
setValue(metaParam, keyProperty, metaResult.getValue(keyProperty));
}
} else {
if (keyColumns.length != keyProperties.length) {
throw new ExecutorException("If SelectKey has key columns, the number must match the number of key properties.");
}
for (int i = 0; i < keyProperties.length; i++) {
//有多个列值，通过列名给对应的列设置值
setValue(metaParam, keyProperties[i], metaResult.getValue(keyColumns[i]));
}
}
}
<insert id=”insert” >
<selectKey keyProperty=”id” resultType=”int” order=”BEFORE”>
-- 插入前填充ID值
SELECT FLOOR(RAND() * 10000) ;
</selectKey>
insert into T_USER (ID, username,pwd) values ( #{id} , #{username} , #{pwd) )
</insert>
