Creating a Bidirectional Relationship in JPA Using ManyToOne

When it comes to mapping entities correctly in Java Persistence API (JPA), annotations and mappedBy come into play. In this article, we will explore how to create a bidirectional relationship between two entities using the ManyToOne annotation.

To begin with, let's consider a scenario where we have two entities: `Tuition` and `Student`. We want to establish a relationship between these two entities such that each `Student` is associated with a unique `Tuition`, and vice versa. In this case, `Tuition` can be considered as the owner of the relationship (owning side), while `Student` is the non-owning side.

One approach to create this bidirectional relationship is to use another foreign key in the `Student` side. However, this would lead to unnecessary duplication in our database model. Instead, we can decide that `Tuition` has a foreign key (FK) that points to `Student`. This makes sense because it does not make sense for `Tuition` to exist without a corresponding `Student`.

To map this relationship correctly, we need to use the ManyToOne annotation on the `Student` side. The `mappedBy` attribute in this annotation tells JPA which field in the owning entity (`Tuition`) is associated with the foreign key.

Here's an example of how you can create this bidirectional relationship using JPA annotations:

```java

@Entity

public class Tuition {

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private Long id;

private String name;

@ManyToOne(cascade = CascadeType.ALL, mappedBy = 'student')

private Student student;

}

@Entity

public class Student {

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private Long id;

private String name;

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)

@JoinColumn(name = 'student_id', referencedColumnName = 'id')

private List tuitionList;

}

```

In this example, the `Tuition` entity has a ManyToOne relationship with the `Student` entity, and the `Student` entity has a OneToMany relationship with the `Tuition` entity. The `cascade` attribute is used to propagate changes from the owning side (`Tuition`) to the non-owning side (`Student`).

By using JPA annotations in this way, we can create bidirectional relationships between two entities and manage them easily in our application.

Jpa manytoone