Hibernate how to use a constant as part of composite foreign reference

Question

I have a master table A with a composite primary key, consisting of two columns. One of these columns is a constant (\"THE CONSTANT VALUE\"

Answer 1

I really wonder how it can be helpful to have a constant column value in a database, but anyway...

What I would do is to only map the non-constant column as ID, and make the constant column a regular column, with a constant value:

@Entity
public class Strange {
    @Id
    private Long id;

    @Column
    private long constant = 345; // the constant that you want in your database

    @OneToMany(mappedBy = "strange")
    private Set details;

    ...
    // no setter for constant!
}

@Entity
public class Detail {
   ...
   @ManyToOne
   @JoinColumn(name = "strange_id")
   private Strange strange;
}

If other entities reference this same Strange entity using its full composite key, then simply do the following:

@Entity
public class Strange {
    @Id
    @Column(name = "strange_id")
    private Long id;

    @Id
    private long constant = 345; // the constant that you want in your database

    @OneToMany(mappedBy = "strange")
    private Set details;

    ...
    // no setter for constant!
}

@Entity
public class Detail {
   ...
   @ManyToOne
   @JoinColumn(name = "strange_id", referencedColumnName = "strange_id")
   private Strange strange;
}

You can reference other entities using something other than their PK. Another unique column is also OK. And since strange_id is unique, it fits the bill. The referencedColumnName attribute must be used to specify the referenced column name, in that case.