我们是JPA的新手并尝试设置一个非常简单的一对多关系,其中一个名为Message的pojo可以有一个由名为GROUP_ASSOC
的连接表定义的整数组ID列表。这是DDL:
CREATE TABLE "APP"."MESSAGE" ( "MESSAGE_ID" INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1) ); ALTER TABLE "APP"."MESSAGE" ADD CONSTRAINT "MESSAGE_PK" PRIMARY KEY ("MESSAGE_ID"); CREATE TABLE "APP"."GROUP_ASSOC" ( "GROUP_ID" INTEGER NOT NULL, "MESSAGE_ID" INTEGER NOT NULL ); ALTER TABLE "APP"."GROUP_ASSOC" ADD CONSTRAINT "GROUP_ASSOC_PK" PRIMARY KEY ("MESSAGE_ID", "GROUP_ID"); ALTER TABLE "APP"."GROUP_ASSOC" ADD CONSTRAINT "GROUP_ASSOC_FK" FOREIGN KEY ("MESSAGE_ID") REFERENCES "APP"."MESSAGE" ("MESSAGE_ID");
这是pojo:
@Entity
@Table(name = "MESSAGE")
public class Message {
@Id
@Column(name = "MESSAGE_ID")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int messageId;
@OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.PERSIST)
private List groupIds;
public int getMessageId() {
return messageId;
}
public void setMessageId(int messageId) {
this.messageId = messageId;
}
public List getGroupIds() {
return groupIds;
}
public void setGroupIds(List groupIds) {
this.groupIds = groupIds;
}
}
我知道这是错误的,因为groupIds属性没有@Column
映射到GROUP_ASSOC.GROUP_ID
,但希望这说明了我们要做的事情。当我们运行以下测试代码时,我们得到<openjpa-1.2.3-SNAPSHOT-r422266:907835 fatal user error> org.apache.openjpa.util.MetaDataException: The type of field "pojo.Message.groupIds" isn't supported by declared persistence strategy "OneToMany". Please choose a different strategy.
Message msg = new Message();
List groups = new ArrayList();
groups.add(101);
groups.add(102);
EntityManager em = Persistence.createEntityManagerFactory("TestDBWeb").createEntityManager();
em.getTransaction().begin();
em.persist(msg);
em.getTransaction().commit();
帮助!
答案 0 :(得分:3)
当您使用JPA时,您应该考虑对象和对象之间的关系,您应该将对象模型而不是ids
映射到关系模型(可以映射List
JPA 2.0中@ElementCollection
的基本值,但我之前所说的仍然适用。)
在这里,(假设这确实是Message
和GroupAssoc
之间的一对多关系,而不是多对多 Message
和Group
实体之间的关系)你应该有这样的东西:
@Entity
@Table(name = "MESSAGE")
public class Message implements Serializable {
@Id
@Column(name = "MESSAGE_ID")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long messageId;
@OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.PERSIST)
private List<GroupAssoc> groupAssocs = new ArrayList<GroupAssoc>();
public Long getMessageId() {
return messageId;
}
public void setMessageId(Long messageId) {
this.messageId = messageId;
}
public List<GroupAssoc> getGroupAssocs() {
return groupAssocs;
}
public void setGroupAssocs(List<GroupAssoc> groupAssocs) {
this.groupAssocs = groupAssocs;
}
// equals() and hashCode()
}
GroupAssoc
的另一个实体。
PS:你的DDL真的看起来像MESSAGE
和GROUP
之间的(M:N)关系(或者我不理解GROUP_ASSOC
的PK约束)但是你没有' t显示GROUP_ID
上的任何FK约束,所以我不是100%肯定。但如果是这种情况,那么您应该使用@ManyToMany
代替@OneToMany
。