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

I tried to test one-to-many relationship for Hibernate. I defined Post and PostComment entities as below: 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> {
}

and 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>

Then, I used SpringJUnit to add a new post as in PostServiceITTest.java

 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);
    }
}

Unfortunately, the test throw a Postgresql error related to null-violate constraint:

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

I greatly appreciate your time.

Answer 1

您似乎没有为post_id传递值。

Answer 2

In your PostComment class you have a field private Post post . I doubt if you are setting that field.

One option is to add Post post as a constructor argument to PostComment class (along with default constructor) and instantiating it along with Post object as in:

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

and while constructing the object use :

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

instead of

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

Or another approach would be to add scaffolding code in Post class like:

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

and use this method while updating/adding a PostComment to the list in the Post class.

Answer 3

Below code may work; you may set the parent reference in child also...

{       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); 
}

If you are using lombok to generate toString() method, please exclude postComment.post to avoid infinite loop (that leads to stak overflow);

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

Answer 4

I have resolved the issue by dropping my existed database and generating a new one with spring.jpa.hibernate.ddl-auto=create-drop . Of course, you can do it only if you have no valuable data in your database. Once you did it, change back to spring.jpa.hibernate.ddl-auto=update .