java - Spring MyBatis关系映射问题

Question

我使用 MyBatis 和 h2 数据库来进行学习。当我想在查询中将子对象插入到父对象中时遇到问题，然后出现异常。

学生类

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..
}

索引类别

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..
}

学生资料库

@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);
}

索引存储库

@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);
}

异常

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

发生错误是因为你没有指示mybatis如何将Index类型的对象转换为存储在student表中的值(索引 我假设)。

您需要指定如何从可用的对象中获取要存储的值，如下所示:

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