为什么没有在 JPA 中为插入语句分配值

Question

您好，我有几个实体类如下，使用 lombok 作为 getter 和 setter

父实体类有

@Table(name = "PARTY")
@Entity
public class Party {
        
@Id
@Column(name = "PARTY_ID")
private Long partyId;


@OneToMany(targetEntity = DVLoanParticipants.class,cascade = CascadeType.ALL)
@JoinColumn(name = "PARTY_ID")
@MapKey(name="dvpParticipantName")
@LazyCollection(LazyCollectionOption.FALSE)
private Map<String, DVLoanParticipants> dvLoanParticipantsMap;
}

子实体类有

@Table(name = "DV_LOAN_PARTICIPANTS")
@Entity
public class DVLoanParticipants implements Serializable {

@Id
@Column(name = "PARTY_ID")
private Long partyId;

@Id
@Column(name = "DVP_PARTICIPANT_NAME")
private String dvpParticipantName;

@Column(name = "DVP_PARTICIPANT_TYPE")
private String dvpParticipantType;
}

在服务类中，我将保存操作调用为

repository.save(parentEntityObject);

我能够执行更新语句，但是当我尝试为子实体类插入新行时，我收到一个错误提示

cannot insert NULL into ("ABC"."DV_LOAN_PARTICIPANTS"."PARTY_ID")

但如果我在保存操作之前打印 parentEntityObject，我会看到类似的值

(partyId=12345678, dvpParticipantName=XYZ, dvpParticipantType=VKP)

我看到查询格式为

insert 
 into
    DV_LOAN_PARTICIPANTS
    (DVP_PARTICIPANT_TYPE, PARTY_ID, DVP_PARTICIPANT_NAME) 
values
    (?, ?, ?)

就在保存之前，我在对象中看到了值

Builder=DVLoanParticipants(partyId=123456, dvpParticipantName=Builder, 
dvpParticipantType=Individual)

更新

这是值的设置部分

                DVLoanParticipants dvLoanParticipants = new 
           DVLoanParticipants();
                dvLoanParticipants.setPartyId(Long.valueOf(partyId));
                dvLoanParticipants.setDvpParticipantName("Builder");
                dvLoanParticipants.setDvpParticipantType("Individual");
                Party party = new Party();
                Map<String, DVLoanParticipants> dvLoanParticipantsMap = new 
      java.util.HashMap<>();
                dvLoanParticipantsMap.put("Builder", dvLoanParticipants);
                party.setPartyId(Long.valueOf(partyId));
                party.setDvLoanParticipantsMap(dvLoanParticipantsMap);
                repository.save(party);

我做错了什么？

Answer 1

这部分问题的根本原因：

@OneToMany(targetEntity = DVLoanParticipants.class,cascade = CascadeType.ALL)
@JoinColumn(name = "LOAN_ID")
@MapKey(name="dvpParticipantName")
private Map<String, DVLoanParticipants> dvLoanParticipantsMap;

实际上，对于您的情况，@JoinColumn 中的列名意味着：

如果连接是针对使用外键映射策略的单向 OneToMany 映射，外键在目标实体的表中。

因此，为了清楚起见，假设您要映射以下架构：

create table PARTY
(
   PARTY_ID int,
   -- ...

   primary key (PARTY_ID)
);

create table DV_LOAN_PARTICIPANTS
(
   PARTY_ID int,
   DVP_PARTICIPANT_NAME varchar(50),
   DVP_PARTICIPANT_TYPE varchar(10),
   -- ...
   
   primary key (PARTY_ID, DVP_PARTICIPANT_NAME),
   foreign key (PARTY_ID) references PARTY(PARTY_ID)
);

您可以使用以下映射：

@Entity
@Table(name = "PARTY")
public class Party
{
   @Id
   @Column(name = "PARTY_ID")
   private Long partyId;

   // I use fetch = FetchType.EAGER instead of deprecated @LazyCollection(LazyCollectionOption.FALSE)
   // targetEntity = DVLoanParticipants.class is redundant here
   @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
   @JoinColumn(name = "PARTY_ID") // this is DV_LOAN_PARTICIPANTS.PARTY_ID column
   @MapKey(name = "dvpParticipantName")
   private Map<String, DVLoanParticipants> dvLoanParticipantsMap;
   
   public Party()
   {
      dvLoanParticipantsMap = new HashMap<>();
   }

   // getters / setters

   public void addParticipant(DVLoanParticipants p)
   {
      this.dvLoanParticipantsMap.put(p.getDvpParticipantName(), p);
      p.setPartyId(getPartyId());
   }
}

@Entity
@Table(name = "DV_LOAN_PARTICIPANTS")
public class DVLoanParticipants implements Serializable
{
   @Id
   @Column(name = "PARTY_ID")
   private Long partyId;

   @Id
   @Column(name = "DVP_PARTICIPANT_NAME")
   private String dvpParticipantName;

   @Column(name = "DVP_PARTICIPANT_TYPE")
   private String dvpParticipantType;

   // getters / setters
}

以及如何保存的示例：

Party party = new Party();
party.setPartyId(2L);

// ...
DVLoanParticipants part1 = new DVLoanParticipants();
part1.setDvpParticipantName("Name 3");
part1.setDvpParticipantType("T1");
      
DVLoanParticipants part2 = new DVLoanParticipants();
part2.setDvpParticipantName("Name 4");
part2.setDvpParticipantType("T1");

party.addParticipant(part1);
party.addParticipant(part2);

repository.save(party);

还有几个注意事项：

1. LazyCollectionOption.TRUE 和 LazyCollectionOption.FALSE 值是 deprecated，因为您应该使用 @OneToMany 关联的 JPA FetchType 属性。

2. 您使用特定于休眠的方法来映射复合标识符。正如hibernate documentation 中提到的：

复合标识符必须由主键类（例如@EmbeddedId 或@IdClass）表示的限制仅适用于 JPA。

Hibernate 确实允许通过多个@Id 属性在没有主键类的情况下定义复合标识符。

但如果您想获得更多的可移植性，您应该更喜欢 jpa 允许的方法之一。