MyBatis - Mapped Statements collection already contains value for

Mapped Statements collection already contains value for com.sample.mappers.UserMapper...

Two statement blocks with the same id will result in this error. Possible cause:

1. java method overloading in mapper interfaces, as stated by @Lucky
2. There are two statement blocks that use the same id in the same namespace of one or more mapper xml files.

The id findAllId in namespace com.example.UserMapper should be unique.

<mapper namespace="com.example.UserMapper">
 <select id="findAllId" resultType="java.lang.Integer">
    SELECT id FROM User
  </select>
</mapper>

I found out the cause of the error message. If you have the same method name, then mybatis throws the Mapped Statements collection already contains value error message. So the solution is to have different method names for different mapper statements even if the method signatures are different.

So In my mapper interface the method names second getAllUsers() name should be getUserById();. The same error is thrown if you have the same method name in any of the mapper.xml files. So it is mandatory to have unique method names or mapper namespace for different sql statements for mybatis to map this at runtime.

In my case, the occurance was due to resultMaps were added to the Configuration after addition of mapper.

Eg:

Configuration configuration = new Configuration(environment);
configuration.addMappers("com.hemant.data.mapper");
configuration.addResultMap(getResultMapForRoles(configuration));

If we observe MyBatis source code, then on configuration.addMappers(..) ..... parse() is executed. org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parse() org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parseStatement(Method)

for (Method method : methods) {
        try {
          // issue #237
          if (!method.isBridge()) {
            parseStatement(method);
          }
        } catch (IncompleteElementException e) {
          configuration.addIncompleteMethod(new MethodResolver(this, method));
        }
      }

If there is an issue with parsing the statement (which occured in mycase as the statement had @ResultMap annotation, but resultMap wasn't provided to configuration.), the method is added in INCOMPLETE_METHODS in configuration which later raises the exception.

@Select("select role_id, role_name, allowed_actions::bigint, denied_actions::bigint from acm_role")
    @ResultMap("com.hemant.data.mapper.RoleMapper." + PermissionDBHook.ROLE_MAP)
    public List<Role> getAllRoles();

On adding resultMap to configuration before mapper, solved it

   Configuration configuration = new Configuration(environment);
   //Hemant - result map should be added before mappers
   configuration.addResultMap(getResultMapForRoles(configuration));
   configuration.addMappers("com.hemant.data.mapper");

For some reason this error was thrown when I had a resultType set to a class that no longer existed. Once I updated the class, the problem was resolved. Not sure why this particular error was thrown, but perhaps check your resultTypes as well if you come across this.