CODEWITHSUNDEEP
javahibernateinheritance
user3404765
user3404765

Reputation: 41

Table-per-hierarchy strategy without a discriminator column in Hibernate

We have a legacy table and we don't want to add a discriminator column into it. Is it possible to have table-per-hierarchy without a discriminator column?

My parent class code:

@Entity
@Table(name = "SHAPE1")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "Discriminator",
                     discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue(value = "S")

public class Shape {

    @Id
    @Column(name = "Shape_Id")
    int shapeId;

    @Column(name = "Shape_Name")
    String shapeName;

    public Shape() {

    }

    public Shape(int id, String shapeName) {
        this.shapeId = id;
        this.shapeName = shapeName;
    }

    // getters and setters
}

My child class:

@Entity
@DiscriminatorValue(value = "R")
public class Rectangle extends Shape {

    @Column(name = "Rectangle_Length")
    int length;

    @Column(name = "Rectangle_Breadth")
    int breadth;

    public Rectangle() {
    }

    public Rectangle(int id, String shapeName, int length, int breadth) {
        super(id, shapeName);
        this.length = length;
        this.breadth = breadth;
    }

    // getters and setters
}

You can see in my above example, I have to use a discriminator.

Upvotes: 2

Views: 771

Answers (1)

Aslam a
Aslam a

Reputation: 759

SINGLE_TABLE is a very powerful strategy but sometimes, and especially for legacy systems, you cannot add an additional discriminator column. For that purpose Hibernate has introduced the notion of discriminator formula: @DiscriminatorFormula is a replacement of @DiscriminatorColumn and uses an SQL fragment as a formula for discriminator resolution (no need to have a dedicated column).

@Entity
@DiscriminatorFormula("case when forest_type is null then 0 else forest_type end")
public class Forest { ... }

Upvotes: 1

Related Questions