CODEWITHSUNDEEP
javahibernatejpa
Samuel
Samuel

Reputation: 328

MappedSuperclass extending another MappedSuperclass

In JPA/Hibernate, can a mapped super class like BetterBaseEntity be a subclass of another mapped super class BaseEntity ?

I want to retain BaseEntity because nearly everyone uses it but would like to add some new parent functionality.

Upvotes: 4

Views: 2828

Answers (1)

Ritesh
Ritesh

Reputation: 34

Relational databases don’t have a straightforward way to map class hierarchies onto database tables.

To address this, the JPA specification provides several strategies:

MappedSuperclass – the parent classes, can’t be entities

Single Table – the entities from different classes with a common ancestor are placed in a single table

Joined Table – each class has its table and querying a subclass entity requires joining the tables

Table-Per-Class – all the properties of a class, are in its table, so no join is required

Each strategy results in a different database structure.

Entity inheritance means that we can use polymorphic queries for retrieving all the sub-class entities when querying for a super-class.

Since Hibernate is a JPA implementation, it contains all of the above as well as a few Hibernate-specific features related to inheritance.

MappedSuperclass:-

Using the MappedSuperclass strategy, inheritance is only evident in the class, but not the entity model.

Let’s start by creating a Person class which will represent a parent class:

@MappedSuperclass
public class Person {

    @Id
    private long personId;
    private String name;

    // constructor, getters, setters

} Notice that this class no longer has an @Entity annotation, as it won’t be persisted in the database by itself.

Next, let’s add an Employee sub-class:

@Entity
public class MyEmployee extends Person {
    private String company;
    // constructor, getters, setters 
}

In the database, this will correspond to one “MyEmployee” table with three columns for the declared and inherited fields of the sub-class.

If we’re using this strategy, ancestors cannot contain associations with other entities.

For more details refer -

https://ritesh-shukla.blogspot.com/2018/10/hibernate-inheritance-mapping.html?m=1

Upvotes: 1

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