What approaches to inheritance in object mapping in Hibernate are you familiar with?

In Hibernate, there are three main approaches to inheritance mapping of objects to database tables:

1. Single Table (One table per hierarchy)

   • All subclass classes are stored in one table.
   • A special discriminator column is used to determine the object type.
   • Pros: simplicity, high performance during queries.
   • Cons: many nullable columns, possible redundancy.

2. Joined (Joined tables)

   • Each class has its own table.
   • Tables are linked by a key (JOIN).
   • Pros: normalized structure, less duplication.
   • Cons: complex JOIN queries, potentially slower.

3. Table per Class (Table per class)

   • Each class has its own table with fields from all parent classes.
   • UNION is used during selection.
   • Pros: simple table structure.
   • Cons: data duplication, complex queries.

Example annotation for Single Table:

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type")
public abstract class Animal { ... }

@Entity
@DiscriminatorValue("Dog")
public class Dog extends Animal { ... }

The choice of approach depends on performance requirements and data structure.