PersistenceException, Column 'id' specified twice

问题

I have the following files in Play Framework 2.2.3

Controller:

public class Comment extends Controller
{
    public Result create(UUID id)
    {
        models.blog.Blog blog = models.blog.Blog.finder.byId(id);

        Result result;

        if(blog == null)
        {
            result = notFound(main.render("404", error404.render()));
        }
        else
        {
            Form<models.blog.Comment> commentForm = Form.form(models.blog.Comment.class);
            commentForm = commentForm.bindFromRequest();

            if(commentForm.hasErrors())
            {
                result = badRequest(Json.toJson(commentForm));
            }
            else
            {
                models.blog.Comment comment = commentForm.get();

                comment.setId(UUID.randomUUID());
                comment.setTimeCreated(new Date());
                comment.setBlogId(blog.getId());

                comment.save();

                result = ok(Json.toJson(comment));
            }
        }

        return result;
    }
}

And two models

@Entity
@Table(name="blog")
public class Blog extends Model
{
    private static final SimpleDateFormat MONTH_LITERAL = new SimpleDateFormat("MMMMM"),
                                          DAY_NUMBER = new SimpleDateFormat("d"),
                                          YEAR_NUMBER = new SimpleDateFormat("yyyy");
    public static Finder<UUID, Blog> finder = new Finder<UUID, Blog>(UUID.class, Blog.class);

    @Id
    @Column(name="id",length=36, nullable=false)
    public UUID id;

    @OneToOne
    @JoinColumn(name="author_id")
    public User author;

    @Column(name="title",length=255)
    public String title;

    @Column(name="summary",length=255)
    public String summary;

    @Column(name="url",length=255)
    public String url;

    @Column(name="content")
    public String content;

    @Column(name="time_updated")
    public Date time_created;

    @Column(name="time_created", nullable=false)
    public Date time_updated;

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name="blog_id")
    public List<Comment> comments;

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(
    name="blog_tag_map",
    joinColumns={ @JoinColumn(name="blog_id", referencedColumnName="id") },
    inverseJoinColumns={ @JoinColumn(name="tag_id", referencedColumnName="id") }
)
    public List<Tag> tags;

    public List<Comment> getComments()
    {
        return this.comments;
    }
}

@Entity
@Table(name="blog_comment")
public class Comment extends Model
{
    private static final SimpleDateFormat MONTH_LITERAL = new SimpleDateFormat("MMMMM"),
                                          DAY_NUMBER = new SimpleDateFormat("d"),
                                          YEAR_NUMBER = new SimpleDateFormat("yyyy");

    @Id
    @Column(name="id",length=36, nullable=false)
    public UUID id;

    @Column(name="blog_id", length=36)
    public UUID blog_id;

    @ManyToOne
    public Blog blog;

    @Column(name="content", length=500)
    public String content;

    @Column(name="website", length=255)
    public String website;

    @Column(name="name", length=255)
    public String name;

    @Column(name="time_created", updatable=false)
    public Date time_created;
}

I have excluded some setters and getters from these models for brevity, so it doesn't clog up this post.

When I attempt to make a POST request to the aforementioned controller, everything goes fine until I get to the "comment.save()" statement in the controller file, then I get the following error.

I'm unsure why this save isn't going through, and why there is a column conflict. Help much appreciated

回答1:

The issue lies in the fact that you have defined basically two foreign key columns for Blog in your Comment's entity:

@Column(name = "blog_id", length = 36)
public UUID blog_id;

@ManyToOne
public Blog blog;

The default column name for your 'blog' field is: blog_id However, you've already named your 'blog_id' column that. Interestingly, no error/warning is thrown when creating this table...

So when you call comment.save(), the following insert statement is generated:

insert into blog_comment (id, blog_id, content, website, name, time_created, blog_id) values (?,?,?,?,?,?,?)

Notice a reference to 'blog_id' column twice, which is invalid. And this is because of the above double mapping.

To fix, just give your 'blog' property a different name to use for the foreign key column:

@Column(name = "blog_id", length = 36)
public UUID blog_id;

@ManyToOne
@JoinColumn(name = "blogId")
public Blog blog;

I'm not sure why you're mapping your entities like this (perhaps legacy schema?) but the 'blog_id' fields seem to be redundant (and confusing) as you already have an entity mapping in the form of your 'blog' property.

回答2:

This question is pretty old, but for any future reference i have found this answer that solved my problem.

After numerous searchers around the web I found this answer here - thanks to jtal!

Just to summaries the problem:

Using Ebean i have made a @ManyToOne entity that is not implemented in the database in anyway, even more the join field, in your case

blogId

is a valid field that has values of its own.

when trying to join the column on that field, it will always fail because it creates this sql query:

SELECT 
*
FROM
    blog_comment;

select 
    t0.id c0, 
    t0.blog_id c1, 
    t0.content c2, 
    t0.website c3, 
    t0.time_created c4, 
    t0.blog_id c5 <---- notice this duplicate
from 
    blog_comment t0 

in order to solve this, i tell ebean not to use the second set of properties.

your new ebean element should look something like this:

@ManyToOne
@JoinColumn(name = "blogId", insertable = false, updatable = false)
public Blog blog;

hope this helps! =)

来源：https://stackoverflow.com/questions/24377478/persistenceexception-column-id-specified-twice