休眠-映射属性OneToMany。 （如OrderLine）不关联

Question

I'm strugling with JPA. I tried several things but I can't figure out the right way to put the annotations. What is want is like an Order/OrderLine relationship.

Thus:

• Order( PK=orderId, fields=[...])
• OrderLine (Pk1=orderId,Pk2=orderLineId, fields=[...])

Obviously, OrderLine.orderId refers to the 'Order' table.

What I functionally want to do is at least:

• retrieve the Order with and without all orderlines. It should have a Set
• retrieve an orderline by full PK, but without the associated Order.
• retrieve a list of orderlines by orderId.

I only want these 2 tables and classes. nothing more nothing less. I tried several things. Can anybody help me out with putting in the right annotations and members on these two classes?

Edit: what i've done so far. Note that in this real example User=Order and UserRun=OrderLine. So, i am not interested in a seperate 'Run'-entity. Merely a UserRun as described by the Orderline.

@Entity
@Table(name = "user_runs")
public class UserRun {

    @EmbeddedId
    private UserRunKey id;

    public UserRun(){};

    public UserRun(String userName, String runUuid) {
        this.id = new UserRunKey(userName, runUuid);
    }

    public String getUserName() {
        return this.id.getUserName();
    }
    public String getRunUuid() {
        return this.id.getRunUuid();
    }
}

@Embeddable
class UserRunKey implements Serializable {

    @Column(name = "username")
    private String userName;

    @Column(name = "run_uuid")
    private String runUuid;

    public UserRunKey(){};

    public UserRunKey(String userName, String runUuid) {
        this.runUuid = runUuid;
        this.userName = userName;
    }

    public String getUserName() {
        return userName;
    }

    public String getRunUuid() {
        return runUuid;
    }

}

This created a userruns/orderline table with the PK in the wrong way: create table user_runs (run_uuid varchar(255) not null, username varchar(255) not null, primary key (run_uuid, username))

1. I want the primary key in reverse.
2. I want username as FK to User
3. I want a Set in my User-class.

When I do the following in my User-class:

@OneToMany
private Set<UserRun> userRuns;

It will create a create table user_user_runs (user_username varchar(255) not null, user_runs_run_uuid varchar(255) not null, user_runs_username varchar(255) not null, primary key (user_username, user_runs_run_uuid, user_runs_username)) And that's something I definitely don't want! Once again, I don't want a Run-object (same as nobody's interested in a Line-class, from OrderLine)

Answer 1

I think I figured it out.

The UserRun/Orderline class:

@Entity
@Table(name = "user_runs")
public class UserRun {

    @EmbeddedId
    private UserRunKey id;

    public UserRun(){};

    public UserRun(String userName, String runUuid) {
        this.id = new UserRunKey(userName, runUuid);
    }

    public String getUserName() {
        return this.id.getUserName();
    }
    public String getRunUuid() {
        return this.id.getRunUuid();
    }
}

@Embeddable
class UserRunKey implements Serializable {

    @Column(name = "username")
    private String userName;

    @Column(name = "run_uuid")
    private String zrunUuid; //starts with a z, so the PK will be pk(username,run_uuid). Apparently, order in PK is determined from the variable names (alphabetic order)....

    public UserRunKey(){};

    public UserRunKey(String userName, String zrunUuid) {
        this.zrunUuid = zrunUuid;
        this.userName = userName;
    }

    public String getUserName() {
        return userName;
    }

    public String getRunUuid() {
        return zrunUuid;
    }

}

In the userclass:

@OneToMany(mappedBy = "id.userName",  fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<UserRun> userRuns;

Unfortunately, there are 2 downsides:

1. I see that there are 2 queries executed instead of a Join on username. One to retrieve user, and 1 to retrieve the Set...

2. I needed to alter variablenames of the PK (compound/Embeddable). It seems there is no clean way to define the PK order. (Seriously?). Fortunately, the variable name is private, and not exposed by getter.

If anybody knows a cleaner way for these 2 issues. Let me know!

Answer 2

I think what you have to do is the following:

• Because the primary key is compound key you need an ID class, as you already did:

   @Embeddable class OrderLinePK implements Serializable { // you can use physical mapping annotations such as @Column here @Column(name="...") private Integer orderLineID; // This is foreign key and the physical mapping should be done // on the entity, and not here private Integer orderID; public OrderLinePK(){} // getters + setters // orverride equals() and hashCode() methods } 

• Implement OrderLine entity

   @Entity public class OrderLine { @EmbededId private OrderLinePK id; @Mapsid("orderID") @ManyToOne @JoinColumn(name = "ORDER_ID", referencedColumn="ID") private Order order; // getters + setters .... } 

• And the Order entity:

   @Entity public class Order { @Id private Integer id; @OneToMany(fetch = FetchType.LAZY) // actually default by 1-to-n private Coolection<OrderLine> orderLines; // getters + setters .... }