Advanced Hibernate (Project Objective)

Inheritance in JPA/Hibernate

Hibernate supports four inheritance strategies to enhance reusability in the entity layer:

1. MappedSuperclass
2. Single Table
3. Joined
4. Table per Class

First Inheritance Strategy: jakarta.persistence.MappedSuperclass

• Annotation: @MappedSuperclass

• Description: A class-level annotation applied to an abstract or concrete superclass. Hibernate does not generate a table for this class.

• Purpose: Defines common fields that can be inherited by other entities.

• Common Members:

  • ID-related: Primary key (e.g., Long id with @Id).
  • Creation Date/Time: @CreationTimestamp for entity creation tracking.
  • Update Date/Time: @UpdateTimestamp for entity update tracking.
  • Versioning: @Version for optimistic locking (e.g., private int myVersion).

• Example:

  @MappedSuperclass
  public abstract class BaseEntity {
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Long id;
  
      @CreationTimestamp
      private LocalDateTime createdAt;
  
      @UpdateTimestamp
      private LocalDateTime updatedAt;
  
      @Version
      private int myVersion;
  
      // Getters and Setters
  }
  
  

Review Note: The MappedSuperclass section is complete, covering the annotation, its purpose, and typical fields. No additional inheritance strategies (Single Table, Joined, Table per Class) were detailed in the input, so I’ll focus on MappedSuperclass as provided. If you need details on the other strategies, let me know.

Associations between Entities (HAS-A)

Associations represent a weaker form of association (aggregation) since entities have standalone lifecycles and separate database identities (tables with primary keys).

Reference: Food Delivery App

• Question: Can one restaurant serve multiple food items?
  • Answer: Yes, this is a one-to-many relationship between Restaurant (one) and FoodItem (many).

2.1 Establish Bidirectional One-to-Many and Many-to-One Association