Spring MyBatis关系映射问题

Question

I am using MyBatis with h2 database for learning purposes. I have a problem when I want to insert child object inside a parent object in a query, then I got an exception.

Student class

public class Student {
  private Long id;
  private String name;
  private Index index;

  public Student(Long id, String name, Index index) {
    this.id = id;
    this.name = name;
    this.index = index;
  }
// getters and setters..
}

Index class

public class Index {
  private Long id;
  private String number;

  public Index() { }

  public Index(Long id, String number) {
    this.id = id;
    this.number = number;
  }
// getters and setters..
}

Student repository

@Mapper
@Repository
public interface StudentRepo {

  @Select("SELECT * FROM student WHERE id=#{id}")
  Student findById(long id);
                 // exception occurs for index field, which is my child object
  @Insert("INSERT INTO student VALUES(#{id}, #{name}, #{index})")
  int insert(Student student);
}

Index repository

@Mapper
@Repository
public interface IndexRepo {

  @Select("SELECT * FROM index WHERE id =#{id}")
  Index findById(long id);

  @Insert("INSERT INTO index VALUES(#{id}, #{number})")
  int insert(Index index);
}

Exception

Caused by: java.lang.IllegalStateException: Type handler was null on parameter mapping for property 'index'. It was either not specified and/or could not be found for the javaType (com.example.batis.domain.Index) : jdbcType (null) combination.
``

Answer 1

The error happens because you did not instructed mybatis how to convert object of type Index to the value that is stored in student table (the id of the Index I assume).

You need to specify how to get the value to be stored from the object that is available like this:

@Insert("INSERT INTO student VALUES(#{id}, #{name}, #{index.id})")
int insert(Student student);

Answer 2

As ave mentioned, I had to put field next to index, so working code is

@Mapper
@Repository
public interface StudentRepo {

  @Select("SELECT * FROM student WHERE id=#{id}")
  Student findById(long id);

  @Insert("INSERT INTO student VALUES(#{id}, #{name}, #{index.id})")
  int insert(Student student);
}