Reverse inheritance mapping in Hibernate

Question

I have a three tables:

Domain

|Field   |Type         |
| id     | BIGINT      |
| domain | VARVHAR(45) |
| other  | ...         |

Url

|Field      |Type         |
| id        | BIGINT      |
| domain_id | BIGINT      |
| url       | VARCHAR(45) |
| other     | ...         |

Data

|Field      |Type                  |
| id        | BIGINT               |
| type      | ENUM('DOMAIN','URL') |
| entity_id | BIGINT               |
| data      | ...                  |

Under other fields, witch contains in Domain and Url tables I understand the some fields, whitch different between themselves by types.

Field entity_id in the Data table must contain the ID from the table Domain or Url depending on value of type fields in the Data table.

How I can create this xml mapping for Hibernate use?

Answer 1

for my opinion, you'd better use @Inheritence and map the Data table with the parent entity like below:

@Entity
@Table(name="MODEL")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="entity_type",discriminatorType=DiscriminatorType.STRING)
public abstract class Model{

@Id
private int id;
//other common attributes
//getters& setters
}

then your Domain and Url classes

@Entity
@DiscriminatorValue(value="domain")
public class Domain extends Model{
private String domain;
//getters&setters
}

//

@Entity
@DiscriminatorValue(value="url")
public class Url extends Model{
@ManyToOne
private Domain domain;

private String url;
//getters & setters
}

and this will create a table named MODEL which will have 2 types (Domain & Url) with an extra column (entity_type) which will take as a value "domain" or "url" depending on the record type.

later in your Data Entity:

@Entity
public class Data{
private int id;
@ManyToOne
private Model model;
}

Ps: you dont need to add type attribute in Data entity anymore while you have the discreminator column entity_type