Can a Discriminator Column be part of the Primary

Question

I'm using Single Table Inheritance in Doctrine2 to store OAuth credentials for multiple services. I'd like to use the service's id as the primary key; however, that's not unique across all services.

I've setup the database to use the discriminator column and the service's id as the primary key, but I can't find a way to make Doctrine use the discriminator column as the key (in addition to the discriminator column). I'm using docblock annotations, and if I add the discriminator column as an @Id field I get an error:

Duplicate definition of column...in a field or discriminator column mapping.

If I only define the field as the discriminator column, any overlapping service ids update all the matching rows.

Anyway to make this work, other than just using an autogenerated it value?

Answer 1

For those who use Hibernate, you can (at least as of JPA 2.1). The following code perfeclty works in my environment (hibernate-entitymanager 4.3.6.Final):

@Entity
@Table(name = "CODIFICATIONS")
@IdClass(CodificationId.class)
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = Codification.DISCRIMINATOR_COLUMN, discriminatorType = DiscriminatorType.INTEGER)
public abstract class Codification implements Serializable {

    public static final String DISCRIMINATOR_COLUMN = "TABLE_ID";

    private static final long serialVersionUID = 1L;

    @Column(name = "CODIFICATION_ID")
    protected Long codificationId;

    @Id
    @Column(name = DISCRIMINATOR_COLUMN, insertable = false, updatable = false)
    protected Long tableId;

    @Id
    @Column(name = "CODE_ID", insertable = false, updatable = false)
    protected Long codeId;

    @Column(name = "LONG_NAME")
    protected String longName;

    @Column(name = "SHORT_NAME")
    protected String shortName;

}

public class CodificationId implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long tableId;
    private Long codeId;

    public Long getTableId() {
        return tableId;
    }

    public void setTableId(Long tableId) {
        this.tableId = tableId;
    }

    public Long getCodeId() {
        return codeId;
    }

    public void setCodeId(Long codeId) {
        this.codeId = codeId;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((tableId == null) ? 0 : tableId.hashCode());
        result = prime * result + ((codeId == null) ? 0 : codeId.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        CodificationId other = (CodificationId) obj;
        if (tableId == null) {
            if (other.tableId != null)
                return false;
        } else if (!tableId.equals(other.tableId))
            return false;
        if (codeId == null) {
            if (other.codeId != null)
                return false;
        } else if (!codeId.equals(other.codeId))
            return false;
        return true;
    }

}

@Entity
@DiscriminatorValue(Status.DISCRIMINATOR_VALUE)
public class Status extends Codification {

    public static final String DISCRIMINATOR_VALUE = "2";

    private static final long serialVersionUID = 1L;

}

Then I configure an association to Status with the following code:

@ManyToOne
@JoinColumnsOrFormulas({
        @JoinColumnOrFormula(formula = @JoinFormula(referencedColumnName = Codification.DISCRIMINATOR_COLUMN, value = Status.DISCRIMINATOR_VALUE)),
        @JoinColumnOrFormula(column = @JoinColumn(name = "STATUS", referencedColumnName = "CODE_ID")) })
private Status status;

Answer 2

You can't, the descriminator column can't be used as part of the primary key.

Why do you need STI for this use-case btw? You have to create one new class per open-id service you provide, sounds pretty annoying :-)