JPA 与实体瞬态字段连接

Question

我有一个带有 Entity @Transient 字段的实体，当我运行查询时出现错误。

查询与实体瞬态字段有连接

@Entity
@Table(name = "OTHER")
public class OtherEntity implements Serializable {
    @Id
    private Long id
   
    @Column( name = "code" )
    private String code;
}

@Entity
@Table(name = "MARKER")
public class MarkerEntity implements Serializable {
    @Id
    private Long id
    
    @Column(name = "OTHER_FIELD")
    private Long otherId;

    @Transient
    private OtherEntity other;

    public MarkerEntity(Long otherId, OtherEntity other) {
        this.otherId = otherId;
        this.other = other;
    }
}

这是 jpa 查询

@Query("SELECT " +
  "new MarkerEntity(" +
  "  o.id, " +
  "  new OtherEntity(o.id, o.code)" +
  ") m " +
  "JOIN OtherEntity o")
public List<MarkerEntity> entities(@Param("id") Long id)

Answer 1

当您尝试将 OtherEntity 与 MarkerEntity 中的瞬态 other 字段连接时，JPA 会抛出错误，因为它不知道如何处理此瞬态关联。您可以使用 @ 定义 MarkerEntity 和 OtherEntity 之间的关系，而不是使用 @Transient 字段多对一。这允许 JPA 自然地处理连接，而不需要瞬态字段。

@Entity @Table(name = "OTHER") public class OtherEntity Implements Serialized { @Id private Long id; @Column(name = "code") 私有字符串代码； // 为 JPA 添加默认构造函数 public OtherEntity() {} public OtherEntity(Long id, String code) { this.id = id; this.code = 代码； } // Getter 和 Setter }

@Entity @Table(name = "MARKER") public class MarkerEntity Implements Serialized { @Id private Long id; @Column(name = "OTHER_FIELD", insertable = false, updateable = false) private Long otherId; @ManyToOne @JoinColumn(name = "OTHER_FIELD",referencedColumnName = "id") private OtherEntity other;公共 MarkerEntity() {} 公共 MarkerEntity(Long otherId, OtherEntity other) { this.otherId = otherId; this.other = 其他； } // Getters 和 Setters } 设置好这种关系后，您的查询可以简化如下

@Query("从 MarkerEntity m 中选择新的 MarkerEntity(m.other.id, m.other)，在此处输入代码em.id = :id")？公共列表实体（@Param（“id”）长id）；