Hibernate database mapping

Question

Firstly, I am somewhat new with Hibernate. To get to know the technology I am using it in a project. I am trying to map the following database:

Campaign
  campaignId(+)
  name

Promotion
  campaignId(+)
  discount(+)
  product
  message

I've indicated the primary key in both cases with a (+). The 'campaignId' in Promotion is a foreign key to Campaign to model the 1:m mapping (A Campaign has many Promotions). Using annotations I am stuck on how to do this.

I do not really want to add a promotionId in the Promotion table as it makes working with the data cumbersome. This of course, makes the bridging table a bit tricky. I also have problems working with a foreign key that is also part of the primary key.

Is a mapping for this possible at all?

Ok, I got it working. Sort of. Have to check if persistence actually work. I did the following:

@Entity
@Table(name = "CAMPAIGNS")
@Audited
public class CampaignEntity {
    private int campaignId;
    private String name;
    private List<PromotionEntity> promotions;

    public CampaignEntity(int campaignId, String name) {
        this.campaignId = campaignId;
        this.name = name;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "cmp_id")
    public int getCampaignId() {
        return campaignId;
    }

    public void setCampaignId(int campaignId) {
        this.campaignId = campaignId;
    }

    // Campaign name here... left out to save space

    @OneToMany
    @JoinColumn(name = "cmp_id")
    public List<PromotionEntity> getPromotions() {
        return promotions;
    }

    public void setPromotions(List<PromotionEntity> promotions) {
        this.promotions = promotions;
    }
}

Promotion is a vanilla mapping (not using embedded after all), with the fields: campaignId, discount, message. (It also does not have a @ManyToOne annotation.)

Does that make sense?

Lastly, and this will be first prize: as you can see I'm using Envers to audit the whole thing. The above creates a rather ugly "CampaignEntity_PromotionEntity_AUD" table. I understand that it is needed, but how can I rename it to CAMPAIGN_PROMOTION_AUD rather?

Thanks guys!

I got an answer on a lonely website deeply hidden away in far-corners of the Hibernate's Jira error tracking website: https://hibernate.onjira.com/browse/HHH-3729.

The answer is to use @AuditJoinTable(name = "CAMPAIGN_PROMOTION_AUD") of course.

Do you mean perhaps that you don't want promotionId in the Campaign table? I'm not sure how that makes sense. — Wouter Lievens
– Wouter Lievens, Commented Mar 26, 2012 at 14:05
Correct, the campaign id should be in the Promotion table as a single column (cmp_id), which is also part of the Promotion's primary key. (see above.) I think I have it with the edited solution above, thanks for the help. — Jaco Van Niekerk
– Jaco Van Niekerk, Commented Mar 26, 2012 at 16:46

Wouter Lievens · Accepted Answer · 2012-03-26 14:07:39Z

1

This is a basic example of a one-to-many relationship and its inverse.

public class Campaign
{
    @OneToMany(mappedBy = "campaign)
    private List<Promotion> promotions;
}

public class Promotion
{
    @ManyToOne
    private Campaign campaign;
}

answered Mar 26, 2012 at 14:07

Wouter Lievens

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5 Comments

Jaco Van Niekerk Over a year ago

This does not quite work... the "Campaign campaign" entry makes it difficult to define it as part of Promotion's primary key. I need "campaign_id" to be the foreign key in this table, while also being part of Promotion's primary key. A "campaign id" together with "discount" defines the entity uniquely.

Wouter Lievens Over a year ago

Why does it need to be part of the primary key? Just use a non-business PK (i.e. an "id" field) and define your business keys as (unique) indexes.

Jaco Van Niekerk Over a year ago

When a campaign is updated from the front-end, I receive a Campaign with a set of Promotions (containing discount, product and message). I now have to write a query to find all the Promotions' PKs, simply to update the Campaign. (Remember, I do not have the PK available from the collection.) That sounds awfully wrong to me.

Wouter Lievens Over a year ago

I'm not sure I understand what you mean. Are you worried that hibernate will fetch data that you do not need?

Jaco Van Niekerk Over a year ago

Hi Wouter... I got it sorted. You are quite correct. Simply clearing the the set in the Campaign and populating it with the new (and modified) Promotion objects worked beautifully. As a Hibernate new-comer I am still reluctant to let Hiberante handle all of the "details". My thanks for your help.

atrain · Accepted Answer · 2012-03-26 14:08:37Z

1

You can use an EmbeddedId to create a multi-field PK.

Remove the PK fields from Promotion
Create a separate entity, say PromotionPK, without any annotations except for @Column on the PK fields
In Promotion, include that PK class as field, annotating it using @EmbeddedId, with getters and setters

The FK mapping is as Wouter indicated.

answered Mar 26, 2012 at 14:08

atrain

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1 Comment

Jaco Van Niekerk Over a year ago

Do you mind giving a short example? I do not know how to map the @ManyToOne annotation using this composite key... where does that go? In the composite key or in the Promotion class?

Jaco Van Niekerk · Accepted Answer · 2012-03-29 06:54:15Z

This is what I am now using. It works well and Hibernate handles the PKs of the Promotions for me. Thanks again.

@Entity
@Table(name = "CAMPAIGNS")
@Audited
public class CampaignEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false)
    private Integer campaignId;

    @Column(name = "name", nullable = false, unique = true)
    private String campaignName;

     @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
     @JoinTable(name = "CAMPAIGN_PROMOTIONS", 
                joinColumns = { @JoinColumn(name = "campaign_id") }, 
                inverseJoinColumns = { @JoinColumn(name = "promotion_id") })
     private Set<PromotionEntity> promotions;

     ...
}

and then, PromotionEntity:

@Entity
@Table(name = "PROMOTIONS")
@Audited
public class PromotionEntity implements Comparable<PromotionEntity> {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "discount", nullable = false)
    private Integer discount;

    @Column(name = "message", nullable = false)
    private String message;

    ...
}

I also prefer annotating the fields rather than the getters as it is more compact and reads easier.

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