Java Spring数据JPA与额外列的多个关系

我一直在努力与链接表中的一个附加列建立多对多关系

这些是我的实体：

    @JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
    public class Post {

    @Id
    @GeneratedValue
    private Long id;

    private String name; 

    @OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
    @JsonIgnore
    private List<PostTag> tags = new ArrayList<>();

    //getters and setters

    public void addTag(Tag tag){
        PostTag postTag = new PostTag(this, tag);
        tags.add(postTag);
        tag.getPosts().add(postTag);
    }

    public void removeTag(Tag tag) {
        for (Iterator<PostTag> iterator = tags.iterator(); 
             iterator.hasNext(); ) {
            PostTag postTag = iterator.next();

            if (postTag.getPost().equals(this) &&
                    postTag.getTag().equals(tag)) {
                iterator.remove();
                postTag.getTag().getPosts().remove(postTag);
                postTag.setPost(null);
                postTag.setTag(null);
            }
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        Post post = (Post) o;
        return id == post.id;
    }

    @Override
    public int hashCode() {
        return Objects.hash(id);
    }   
    }

    @JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
    public class Tag {

    @Id
    @GeneratedValue
    private Long id;

    private String comment;

    @OneToMany(mappedBy = "tag", cascade = CascadeType.ALL, orphanRemoval = true)
    @JsonIgnore
    private List<PostTag> posts = new ArrayList<>();

    //getters and setters

    @Override
    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        Tag that = (Tag) o;
        return id == that.id;
    }

    @Override
    public int hashCode() {
        return Objects.hash(id);
    }
}

@Entity(name = "PostTag")
@Table(name = "post_tag")
@JsonIgnoreProperties({ "hibernateLazyInitializer", "handler" })
public class PostTag {

    @EmbeddedId
    private PostTagId id;

    @ManyToOne(fetch = FetchType.LAZY)
    @MapsId("postId")
    private Post post;

    @ManyToOne(fetch = FetchType.LAZY)
    @MapsId("tagId")
    private Tag tag;

    private Integer impact;

    public FacilityParticipant(Post post, Tag tag) {
        this.post = post;
        this.tag = tag;
        this.id = new PostTagId(post.getId(), tag.getId());
    }

    //getters and setters

    @Override
    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        PostTag that = (PostTag) o;
        return Objects.equals(post, that.post) && Objects.equals(tag, that.tag);
    }

    @Override
    public int hashCode() {
        return Objects.hash(post, tag);
    }
}

@Embeddable
public class PostTagId implements Serializable {

    private Long postId;

    private Long tagId;

    //getters setters

    @Override
    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        PostTagId that = (PostTagId) o;
        return Objects.equals(postId, that.postId) && Objects.equals(tagId, that.tagId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(postId, tagId);
    }
}

当尝试插入这些项目时，我得到一个错误，即我无法将NULL插入（“POST_标记“.ID”）

我尝试过的任何东西，要么会出现其他错误，要么会立即恢复

很可能模型中的某些东西不正确，但我真的不知道它有什么问题

整个建模基于本文

任何帮助都将不胜感激

---

谢谢

spring数据jpa是jpa之上的一层。每个实体都有自己的存储库，您必须处理这个问题。我已经看过上面提到的教程，它是针对JPA的，它还将ID设置为null，这似乎有点不正确，可能是错误的原因。我看起来没那么近。为了处理SpringDataJPA中的问题，您需要一个单独的链接表存储库

@Entity
public class Post {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;

    @OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<PostTag> tags;

@Entity
public class Tag {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;

    @OneToMany(mappedBy = "tag", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<PostTag> posts;

@Entity
public class PostTag {
    @EmbeddedId
    private PostTagId id = new PostTagId();

    @ManyToOne(fetch = FetchType.LAZY)
    @MapsId("postId")
    private Post post;

    @ManyToOne(fetch = FetchType.LAZY)
    @MapsId("tagId")
    private Tag tag;

    public PostTag() {}
    public PostTag(Post post, Tag tag) {
        this.post = post;
        this.tag = tag;
    }

@SuppressWarnings("serial")
@Embeddable
public class PostTagId implements Serializable {
    private Long postId;
    private Long tagId;
    @Override
    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        PostTagId that = (PostTagId) o;
        return Objects.equals(postId, that.postId) && Objects.equals(tagId, that.tagId);
    }
    @Override
    public int hashCode() {
        return Objects.hash(postId, tagId);
    }

注意，几乎没有变化。我没有明确设置

PostTagId

id。这些由持久层（本例中为hibernate）处理

还请注意，您可以使用自己的repo明确更新

PostTag

条目，也可以从列表中添加和删除它们，因为

CascadeType.ALL

已设置，如图所示。对spring数据jpa使用

CascadeType.ALL

的问题在于，即使预取联接表实体，spring数据jpa仍会再次执行该操作。试图通过级联类型更新关系。新实体的所有都有问题

如果没有

CascadeType

，

posts

或

tags

列表（应该设置）都不是关系的所有者，因此添加到它们就无法实现持久性，只能用于查询结果

在阅读

PostTag

关系时，您需要专门获取它们，因为您没有

FetchType.EAGER

。

FetchType.EAGER

的问题是，如果您不想要连接，并且如果您将其同时放在

Tag

和

Post

上，那么您将创建一个递归的获取，该获取可以用于任何查询的所有

标记和
Posts

@Query("select t from Tag t left outer join fetch t.posts tps left outer join fetch tps.post where t.id = :id")
Tag getOneWithPosts(@Param("id") Long id);

最后，一定要检查日志。注意，创建关联需要SpringDataJPA（我认为jpa）读取现有表，以查看关系是新的还是更新的。无论您是自己创建并保存
PostTag
，还是预取列表，都会发生这种情况。JPA有一个单独的合并，我认为你可以更有效地使用它

create table post (id bigint generated by default as identity, primary key (id))
create table post_tag (post_id bigint not null, tag_id bigint not null, primary key (post_id, tag_id))
create table tag (id bigint generated by default as identity, primary key (id))
alter table post_tag add constraint FKc2auetuvsec0k566l0eyvr9cs foreign key (post_id) references post
alter table post_tag add constraint FKac1wdchd2pnur3fl225obmlg0 foreign key (tag_id) references tag

Step 1
insert into tag (id) values (null)
insert into post (id) values (null)
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

Step 2
insert into post (id) values (null)
insert into tag (id) values (null)
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

Step 3
select tag0_.id as id1_2_0_, posts1_.post_id as post_id1_1_1_, posts1_.tag_id as tag_id2_1_1_, post2_.id as id1_0_2_, posts1_.tag_id as tag_id2_1_0__, posts1_.post_id as post_id1_1_0__ from tag tag0_ left outer join post_tag posts1_ on tag0_.id=posts1_.tag_id left outer join post post2_ on posts1_.post_id=post2_.id where tag0_.id=?
select tag0_.id as id1_2_1_, posts1_.tag_id as tag_id2_1_3_, posts1_.post_id as post_id1_1_3_, posts1_.post_id as post_id1_1_0_, posts1_.tag_id as tag_id2_1_0_ from tag tag0_ left outer join post_tag posts1_ on tag0_.id=posts1_.tag_id where tag0_.id=?
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

Step 4 -- better
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

可能您错过了PostTag实体上的@IdClass（PostTagId.class）？如果没有它，它应该可以工作。这里的最后一个解决方案是什么：仍然不工作：(
@Query("select t from Tag t left outer join fetch t.posts tps left outer join fetch tps.post where t.id = :id")
Tag getOneWithPosts(@Param("id") Long id);

create table post (id bigint generated by default as identity, primary key (id))
create table post_tag (post_id bigint not null, tag_id bigint not null, primary key (post_id, tag_id))
create table tag (id bigint generated by default as identity, primary key (id))
alter table post_tag add constraint FKc2auetuvsec0k566l0eyvr9cs foreign key (post_id) references post
alter table post_tag add constraint FKac1wdchd2pnur3fl225obmlg0 foreign key (tag_id) references tag

Step 1
insert into tag (id) values (null)
insert into post (id) values (null)
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

Step 2
insert into post (id) values (null)
insert into tag (id) values (null)
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

Step 3
select tag0_.id as id1_2_0_, posts1_.post_id as post_id1_1_1_, posts1_.tag_id as tag_id2_1_1_, post2_.id as id1_0_2_, posts1_.tag_id as tag_id2_1_0__, posts1_.post_id as post_id1_1_0__ from tag tag0_ left outer join post_tag posts1_ on tag0_.id=posts1_.tag_id left outer join post post2_ on posts1_.post_id=post2_.id where tag0_.id=?
select tag0_.id as id1_2_1_, posts1_.tag_id as tag_id2_1_3_, posts1_.post_id as post_id1_1_3_, posts1_.post_id as post_id1_1_0_, posts1_.tag_id as tag_id2_1_0_ from tag tag0_ left outer join post_tag posts1_ on tag0_.id=posts1_.tag_id where tag0_.id=?
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)

Step 4 -- better
select posttag0_.post_id as post_id1_1_0_, posttag0_.tag_id as tag_id2_1_0_ from post_tag posttag0_ where posttag0_.post_id=? and posttag0_.tag_id=?
insert into post_tag (post_id, tag_id) values (?, ?)