CODEWITHSUNDEEP
javajpaprimary-keyplayframework
user393964
user393964

Reputation:

JPA primary key value is always 0

I have a post class and it kind of works, but there's one problem: the primary key doesn't increase.

@Entity
@Table(name="posts")
public class Post extends GenericModel{

    @Id
    @Column(name="post_id")
    public int id;

    @Column(name="post_situation")
    public String situation;

    @Column(name="post_date")
    public Date date;

    @Column(name="post_userid")
    public int userid;

    @OneToMany(mappedBy="post", cascade=CascadeType.ALL)
    public List<Block> blocks;

    public Post addBlock(String content, int position){
        Block b = new Block(this, content, position);
        b.save();

        this.blocks.add(b);

        this.save();
        return this;
    }

    public Post(String situation, Date date){
        this.situation = situation;
        this.date = date;
        this.userid = 2;
    }

}

When I call it the first time on an empty table, it works fine, but the second time, I'm getting PersistenceException occured : org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update The post_id column always has 0. Any idea how to fix this? I have the @Id annotation in palce..

This is how I have in my controller:

    Post p = new Post("Midden in het middenoosten.", new Date()).save();

Any ideas what's causing this problem?

Upvotes: 3

Views: 5760

Answers (2)

Thadeuse
Thadeuse

Reputation: 1803

There are several strategies available to generate id:

  1. GenerationType.AUTO
  2. GenerationType.SEQUENCE
  3. GenerationType.IDENTITY
  4. GenerationType.TABLE

If you want the primary key values to be auto-generated, use GenerationType.AUTO, it works with MySQL.

Upvotes: 1

Vineet Reynolds
Vineet Reynolds

Reputation: 76709

It seems that you want the primary key values to be auto-generated. If that is the case, if you'll need to add the @GeneratedValue annotation to the id attribute, in addition to the @Id annotation. Your code should therefore be:

@Id
@Column(name="post_id")
@GeneratedValue
public int id;

There are several strategies available to generate the Ids. You would have to read up on those to decide if you want to choose the TABLE -based, SEQUENCE -based or the IDENTITY -based strategy (which depends on what your database supports). If you choose a strategy explicitly, the define strategy will be used, instead of the default AUTO strategy. Explicit strategy decisions, are communicated in code as:

@Id
@Column(name="post_id")
@GeneratedValue(strategy=SEQUENCE, generator="POST_SEQ")
public int id;

Without generated values, the default value for integers in Java, i.e. 0 will be persisted for the post_id column. Due to the primary key constraint, you cannot have a second row with the same key, resulting in the described failure.

Upvotes: 5

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