mybatis源码追踪2——将结果集映射为map

org.apache.ibatis.binding.MapperMethod中execute方法

...
} else if (method.returnsMap()) {
    result = executeForMap(sqlSession, args);
} else {
...

  private <K, V> Map<K, V> executeForMap(SqlSession sqlSession, Object[] args) {
    Map<K, V> result;
    Object param = method.convertArgsToSqlCommandParam(args);
    if (method.hasRowBounds()) {
      RowBounds rowBounds = method.extractRowBounds(args);
      result = sqlSession.<K, V>selectMap(command.getName(), param, method.getMapKey(), rowBounds);
    } else {
      result = sqlSession.<K, V>selectMap(command.getName(), param, method.getMapKey());
    }
    return result;
  }

映射为map时有个可自定义的参数：mapkey

    private String getMapKey(Method method) {
      String mapKey = null;
      if (Map.class.isAssignableFrom(method.getReturnType())) {
        final MapKey mapKeyAnnotation = method.getAnnotation(MapKey.class);
        if (mapKeyAnnotation != null) {
          mapKey = mapKeyAnnotation.value();
        }
      }
      return mapKey;
    }

通过org.apache.ibatis.annotations.MapKey可以配置该参数，该参数应与sql中select的字段一致且为大写。

最终的resultHandler：

public class DefaultMapResultHandler<K, V> implements ResultHandler {

  private final Map<K, V> mappedResults;
  private final String mapKey;
  private final ObjectFactory objectFactory;
  private final ObjectWrapperFactory objectWrapperFactory;

  @SuppressWarnings("unchecked")
  public DefaultMapResultHandler(String mapKey, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory) {
    this.objectFactory = objectFactory;
    this.objectWrapperFactory = objectWrapperFactory;
    this.mappedResults = objectFactory.create(Map.class);
    this.mapKey = mapKey;
  }

  public void handleResult(ResultContext context) {
    // TODO is that assignment always true?
    final V value = (V) context.getResultObject();
    final MetaObject mo = MetaObject.forObject(value, objectFactory, objectWrapperFactory);
    // TODO is that assignment always true?
    final K key = (K) mo.getValue(mapKey);
    mappedResults.put(key, value);
  }

  public Map<K, V> getMappedResults() {
    return mappedResults;
  }
}