Spring Boot @OneToMany

In Spring Boot, the @OneToMany annotation is a powerful tool that is used to establish a one-to-many relationship between two entities. It allows developers to create a relationship between two entities, where one entity has a collection of another entity. This blog post will explain the @OneToMany annotation and its usage in Spring Boot.

What is the @OneToMany Annotation?

The @OneToMany annotation is used to define a one-to-many relationship between two entities. It allows one entity to have a collection of another entity. The relationship between the two entities is established by adding a foreign key column to the child entity that references the primary key column of the parent entity.

Usage of @OneToMany Annotation:

Here are some use cases of the @OneToMany annotation in Spring Boot:

• One-To-Many Unidirectional Relationship:
  In a unidirectional relationship, only one entity has a reference to the other entity. In this case, the @OneToMany annotation is added to the parent entity to define the relationship. Here is an example:

@Entity
public class Parent {
    @Id
    private Long id;
    private String name;

    @OneToMany(cascade = CascadeType.ALL)
    private List<Child> children;
}

@Entity
public class Child {
    @Id
    private Long id;
    private String name;
}

• One-To-Many Bidirectional Relationship:
  In a bidirectional relationship, both entities have a reference to each other. In this case, the @OneToMany annotation is added to the parent entity, and the @ManyToOne annotation is added to the child entity. Here is an example:

@Entity
public class Parent {
    @Id
    private Long id;
    private String name;

    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL)
    private List<Child> children;
}

@Entity
public class Child {
    @Id
    private Long id;
    private String name;

    @ManyToOne
    @JoinColumn(name = "parent_id")
    private Parent parent;
}

Conclusion:

In conclusion, the @OneToMany annotation is an essential tool for establishing a one-to-many relationship between two entities in Spring Boot. It is a powerful tool that allows developers to create complex relationships between entities. By using the @OneToMany annotation, developers can write more robust and reliable code that is easy to maintain and understand.