在 JPA 中使用 oneToMany 关系时，Postgresql 在列中抛出空值违反了非空约束

Question

我尝试测试 Hibernate 的一对多关系。我将 Post 和 PostComment 实体定义如下： Post.java

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;

@Entity
@Table(name = "post")
public class Post {

    @Id
    @Column(name="post_id")
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    private Long postId;

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

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

    public Post() {};

    public Post(String title) {
        this.title = title;
    }
   // Add getter and setter
}

PostComment.java

    import javax.persistence.*;

@Entity
@Table(name = "post_comment")
public class PostComment {
    @Id
    @Column(name="comment_id")
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    private Long commentId;

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

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "post_id")
    private Post post;

    public PostComment() {};
    public PostComment(String review) {
        this.review = review;
    }
    // Add getter and setter
}

PostRepository.java

public interface PostRepository extends JpaRepository<Post,Long> {
}

和db-changelog.xml

<changeSet id="1" author="dev">
    <createTable tableName="post_comment">
        <column name="comment_id" type = "bigint">
            <constraints nullable="false" primaryKey="true"></constraints>
        </column>
        <column name="review" type="varchar(255)"></column>
    </createTable>
    <createTable tableName="post">
        <column name="post_id" type="bigint">
            <constraints nullable="false" primaryKey="true"></constraints>
        </column>
        <column name="title" type = "varchar(255)"></column>
    </createTable>
</changeSet>

然后，我使用 SpringJUnit 在 PostServiceITTest.java 中添加新帖子

 import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.annotation.DirtiesContext;
import org.springframework.test.context.ActiveProfiles;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.web.WebAppConfiguration;

import java.util.Arrays;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = {Application.class})
@WebAppConfiguration
@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_CLASS)
@ActiveProfiles("devmock")
public class PostServiceITTest {
    @Autowired
    private PostRepository postRepository;

    @Test
    public void testAddPost(){
        Post post = new Post(" Post 1");

        PostComment postComment1 = new PostComment(" Post comment 1");  
        PostComment postComment2 = new PostComment(" Post comment 2");
        post.setComments(Arrays.asList(postComment1,postComment2));

        postRepository.save(post);
    }
}

不幸的是，测试抛出了一个与 null-violate 约束相关的 Postgresql 错误：

    Caused by: org.postgresql.util.PSQLException: ERROR: null value in column "post_id" violates not-null constraint
  Detail: Failing row contains (null,  Post 1).

非常感谢您的宝贵时间。

Answer 1

您似乎没有传递post_id 的值。

Answer 2

在您的PostComment 类中，您有一个字段private Post post。我怀疑你是否设置了那个字段。

一种选择是将Post post 作为构造函数参数添加到PostComment 类（连同默认构造函数），并将其与Post 对象一起实例化，如下所示：

public PostComment(String review, Post post) {
  this.review = review;
  this.post = post;
}

在构造对象时使用：

PostComment postComment1 = new PostComment(" Post comment 1", post);

而不是

PostComment postComment1 = new PostComment(" Post comment 1");

或者另一种方法是在 Post 类中添加脚手架代码，例如：

public void addPostComment(PostComment comment) {
    comments.add(comment);
    comment.setPost(this);
}

并在将PostComment 更新/添加到Post 类中的列表时使用此方法。

Answer 3

我已通过删除现有数据库并使用spring.jpa.hibernate.ddl-auto=create-drop 生成新数据库来解决此问题。当然，只有在数据库中没有有价值的数据时才能这样做。完成后，改回spring.jpa.hibernate.ddl-auto=update。

Answer 4

以下代码可能有效；您也可以在 child 中设置父引用...

{       Post post = new Post(" Post 1");

        PostComment postComment1 = new PostComment(" Post comment 1");  
        postComment1.setPost(post); // < -- here
        PostComment postComment2 = new PostComment(" Post comment 2");
        postComment2.setPost(post); // < -- here

        post.setComments(Arrays.asList(postComment1,postComment2));

        postRepository.save(post); 
}

如果您使用lombok生成toString()方法，请排除postComment.post以避免无限循环（导致stak溢出）；

@ToString(exclude = { "post" })
public class PostComment{
// ...
}