how to force a no-argument constructor

[junglechange]

When the order of the sql statement columns and the parameter list of the constructor are not the same, it is easy to make mistakes with the parameter constructor

https://github.com/mybatis/mybatis-3/blob/7f783984692b146154de5b37d351c17f1c904ded/src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java#L720

[harawata]

Hello @junglechange ,

Sorry, I couldn't understand what you mean. Please provide a test case or demo project like these so that we can reproduce the problem on our end.

[h3adache]

If you are trying to make it always use the no arg constructor then use the AutomapConstructor annotation. Or simply do not use constructor mapping.

[junglechange]

create table user ( name varchar(32), info varchar(32) ); insert into user(name, info) VALUES ('hello', 'world');

static class User {
    private String info;
    private String name;

    public User(String info, String name) {
        this.info = info;
        this.name = name;
    }

    public String getInfo() {
        return info;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "User{" +
                "info='" + info + '\'' +
                ", name='" + name + '\'' +
                '}';
    }
}

@Mapper
interface UserMapper {
    @Select("select name,info as abc from user")
    List<User> findAll();
}

call UserMapper.findAll

Expected result

[User{info=null, name='hello'}]

Actual result

[User{info='hello', name='hello'}]

[harawata]

Your User class does not have a no-arg constructor. MyBatis (or anyone) cannot call a constructor that does not exist.

Any of the following should resolve your problem.

1. Add the no-arg constructor
2. Use a result map with <constructor /> or @ConstructorArgs
3. Change the result column order to name, info

There also is an ongoing discussion about an enhancement to use argument names for mapping. See #2192 #2196

[harawata]

No response. Closing.