Question

我正在将MyBatis与h2数据库一起用于学习目的。当我想在查询的父对象中插入子对象时遇到问题，然后出现异常。

学生班

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

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);
}

例外

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

发生错误是因为您没有指示mybatis如何将类型Index的对象转换为存储在student表中的值（我假设的Index的ID）。

您需要指定如何从这样的可用对象中获取要存储的值：

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

Answer 2

如前所述，我必须将字段放在索引旁边，所以工作代码是

@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);
}

Spring MyBatis关系映射问题

2 个答案: