Question

我正在尝试建立一个与此处显示的系统非常相似的系统：

https://vladmihalcea.com/the-best-way-to-use-the-manytomany-annotation-with-jpa-and-hibernate/

使用以下所示的内容类以相同的方式设置PostgreSQL模式，映射到具有content_id和tag_id的表中的标记类，这些表在其各自的表上具有外键约束。我遇到的问题是尝试保留新的内容对象时，我正在检查对象的标签是否存在，如果存在，则使用addTag方法添加它们，然后保留对象。否则，我将创建它们并保留该对象。执行此操作的POST方法也如下所示。存储库成功找到了标记，因为它们已经被保留了，但是当我尝试随后保留内容时出现以下错误： org.postgresql.util.PSQLException：错误：在表上插入或更新

"content_tag" violates foreign key constraint "tag_id_fkey"
  Detail: Key (tag_id)=(11) is not present in table "tag".

我逐步执行了代码，并使用addTag方法将标记添加到内容中时，它表明它们的ID与数据库中已经存在的标记匹配，所以我不明白为什么当我保留内容时它是一个不同的ID。有谁知道我如何防止这种情况的发生并让内容持续存在？

@Entity(name = "Content")
@Table(name = "content")
@TypeDef( name= "StringJsonObject", typeClass = StringJsonUserType.class)
public class Content implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Type(type = "StringJsonObject")
    @Column(name = "text")
    private String text;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    @ManyToMany(cascade = {
            CascadeType.MERGE
    })
    @JoinTable(name = "content_tag",
            joinColumns = @JoinColumn(name = "tag_id"),
            inverseJoinColumns = @JoinColumn(name="content_id")
    )
    private Set<Tag> tags = new HashSet<>();

    public Set<Tag> getTags() {
        return tags;
    }

    public void setTags(Set<Tag> tags) {
        this.tags = tags;
    }

    public void addTag(Tag tag) {
        tags.add(tag);
        tag.getContents().add(this);
    }

    public void removeTag(Tag tag) {
        tags.remove(tag);
        tag.getContents().remove(this);
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Content)) return false;
        return id != null && id.equals(((Content) o).getId());
    }

    @Override
    public int hashCode() {
        return 31;
    }
}

@Entity(name = "Tag")
@Table(name = "tag")
public class Tag implements Serializable {

    @Id
    @GeneratedValue
    private Long id;

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

    @ManyToMany(mappedBy = "tags")
    private Set<Content> contents = new HashSet<>();

    public Tag() {}

    public Tag(String name) {
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<Content> getContents() {
        return contents;
    }

    public void setContents(Set<Content> contents) {
        this.contents = contents;
    }

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

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

@PostMapping(value = "/content", consumes = { MediaType.APPLICATION_JSON_VALUE },
        produces = { MediaType.APPLICATION_JSON_VALUE })
public ContentJSON createContent(@RequestBody(required = false) final String payload) {
    if (StringUtils.isEmpty(payload)) {
        throw new IllegalArgumentException(ServiceErrorCode.INVALID_REQUEST_BODY);
    }
    final ContentRequest request = convertPayloadToRequest(payload, ContentRequest.class);
    final Content content = new Content();
    content.setText(request.getContent().getText().toString());

    for (final String tag : request.getContent().getTags()) {
        final List<Tag> current = tagRepository.findByName(tag);
        if (current.isEmpty()) {
            final Tag newTag = new Tag(tag);
            tagRepository.save(newTag);
            content.addTag(newTag);
        } else {
            content.addTag(current.get(0));
        }

    }
    final Content response = contentRepository.save(content);

    Set<String> tagNames = new HashSet<>();
    for (final Tag tag : content.getTags()) {
        tagNames.add(tag.getName());
    }
    return new ContentJSON(response, tagNames);
}

Answer 1

问题是下面的注释。

@JoinTable(name = "content_tag",
        joinColumns = @JoinColumn(name = "content_id"),
        inverseJoinColumns = @JoinColumn(name="tag_id")
)

joinColumns和inverseJoinColumns被反转

关于ManyToMany关系的PostgreSQL约束违反错误，但是应该存在外键

1 个答案: