UniqueConstraint on foreign key (ManyToOne).

[Gasan Guseynov]

Hi, guys.

Searched for the answer, but didn't find.

Here is what I have:

import javax.persistence.JoinColumn;
import javax.persistence.UniqueConstraint;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name = "worm"
    , uniqueConstraints = {
            @UniqueConstraint(columnNames={"apple_id", "watermelon_id"})
    }
)

public class Worm implements Serializable {
    private static final long serialVersionUID = 8641133221628376834L;

    @ManyToOne
    protected Apple apple;
    
    @ManyToOne(fetch=FetchType.EAGER)
    protected Watermelon watermelon;
    
    public void setApple(Apple apple) {
        this.apple = apple;
    }

    public Apple getApple() {
        return apple;    
    }

    public void setWatermelon(Watermelon watermelon) {
        this.watermelon = watermelon;
    }

    public Watermelon getWatermelon() {
        return watermelon;    
    }
}

I think you inferred what is the problem. Yes, constraints aren't created. Just messed up with this.

[James Sutherland]

What error are you getting?

You Entity does not have an @Id, so is not valid. You seem to want both ManyToOne foreign keys to be the Id?

In JPA 2.0 you can just add @Id to both.

In JPA 1.0, it is more complex, see,
http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns

You object also seems to just be a many-to-many join table, if you mapped it as a ManyToMany, you would not need a class for it at all.

[Gasan Guseynov]

Hi James.

Thanks for your answer it seems meaningful.

I'm sorry, I just forgot the @Id property, heh. So I have it. I want that 2 to be not ID, but simply unique. Unique constraint on (apple_id, watermelon_id) that are foreign keys. Stupid isn't it? But, for my misery, this is what I want.

[Gasan Guseynov]

By the way, thanks for the link. JPA 1.0 or 2.0 Just don't know, I always thought that JPA is JPA without versions. By the way, I'm using Hibernate, so maybe it doesn't matter what JPA version it is. It's simple annotations isn't it?