Entity Relationship Overview

Restaurant Entity

• Extends: BaseEntity
• Attributes:
  • private String name;
  • private String address;
  • private String city;
  • private String description;
  • Association:
    • @OneToMany(mappedBy = "myRestaurant", cascade = CascadeType.ALL)
    • private List<FoodItem> foodItems = new ArrayList<>();(Initialized to avoid NullPointerException)
• Role: Parent, non-owning (inverse) side of the bidirectional association.
• Project Tip: Exclude foodItems from toString() to prevent infinite recursion (stack overflow).

FoodItem Entity

• Attributes:
  • private String itemName;
  • private String itemDescription;
  • private boolean isVeg;
  • private int price;
  • Association:
    • @ManyToOne
    • @JoinColumn(name = "restaurant_id")
    • private Restaurant myRestaurant;
• Role: Child, owning side of the bidirectional association (contains the foreign key).
• Note: In a one-to-many bidirectional relationship, the many side (FoodItem) is always the owning side to maintain normalization.

JPA Annotations for Associations

• @OneToMany
• @ManyToOne
• @OneToOne
• @ManyToMany

Problem with Bidirectional Association

• Issue: Hibernate creates an unnecessary join table (e.g., restaurants_food_items) because it cannot automatically determine the owning and inverse sides in a bidirectional association.
• Cause: Lack of explicit ownership definition in the @OneToMany annotation.
• Solution: Use the mappedBy attribute in the @OneToMany annotation on the inverse side (Restaurant).
  • Syntax: @OneToMany(mappedBy = "myRestaurant")
  • Explanation: mappedBy specifies the property name (myRestaurant) on the owning side (FoodItem) that manages the foreign key.

Customizing Foreign Key