Mapping a one to many relationship in Hibernate?

Question

I have two tables, a user table and a user_avatar table. For each user, there are 3 records in the user_avatar table, for 3 sizes of avatars (large, medium, small).

The user_avatar table has a userId column which refers to the User.id field to specify to which user an avatar belongs to.

Here's my UserAvatar class:

@Entity @Table(name = "user_avatar") public class UserAvatar { @Id @GeneratedValue private long id; @ManyToOne @JoinColumn(name = "userId") private User user; @Enumerated(EnumType.STRING) private AvatarSize size; private String file; private String s3Key; @Override public String toString() { return size + " " + file; } }

And here's how I'm referring to it in the `user

@Entity public class User { @Id @GeneratedValue public Long id; @OneToMany @JoinColumn(name = "id") @OrderColumn(name = "id") public UserAvatar[] avatar; //declared array as there'd be at least 3 records }

When I run this code, I get the error:

Repeated column in mapping for collection: com.xxx.User.avatar column: id

What am I doing wrong?

stackoverflow.com/questions/3657197/hibernate-onetomany-mapping — kosa
– kosa, Commented Feb 26, 2014 at 17:05

Community · Accepted Answer · 2017-05-23 10:26:11Z

What you are doing here is a bidrectional many-to-one, where you want to populate objects on both sides of the relationship.

Hibernate will complain if you have a JoinColumn on both sides, so just put it on the "owning" side and add mappedBy to the other side.

See this example:

public class UserAvatar { ... @ManyToOne @JoinColumn(name="userId") // userId is the name of your database FK column private User user; ... } public class User { ... @OneToMany(mappedBy="user") public List<UserAvatar> avatars; ... }

As for the particular error you were getting, I believe that was caused by JoinColumn("id") in User conflicting with the primary key column id.

Also see this SO answer.

Peter Bratton · Accepted Answer · 2014-02-26 17:04:32Z

1

Hibernate will maintain an association's order when you use a List or an array. To do that, it needs an integer column in the many-side table to store the record's position in the List/array. You can either:

Change your field to use a Set, for which Hibernate will not attempt to maintain ordering.
Add an integer type column to your database to store the record order, and name that in the @OrderColumn annotation.

answered Feb 26, 2014 at 17:04

Peter Bratton

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6 Comments

Peter Bratton Over a year ago

Looks like it to me, at least according to your description.

Ali Over a year ago

I changed UserAvatar[] to Set<UserAvatar>, and now I get this:

org.hibernate.AnnotationException: @OneToOne or @ManyToOne on com.xxx.User.avatar references an unknown entity: java.util.Set

Peter Bratton Over a year ago

You need to map both sides. @ManyToOne goes on the One side, @OneToMany goes on the collection side.

Peter Bratton Over a year ago

I would highly recommend working through a tutorial before going any further.

Ali Over a year ago

I'm now getting Repeated column in mapping for collection: com.xxx.User.avatar column: id after my last edit. Totaly stumped on what I'm doing wrong

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