Steps to Implement Collection Mapping
Below are the steps to implement JPA Collection Mapping.
Step 1: Define the Entities
We can define the Entity classes in JPA that represent the objects that are persisted in the database and these classes are annotated with the @Entity.
Example:
@Entity
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@ManyToMany
@JoinTable(name = "student_course",
joinColumns = @JoinColumn(name = "student_id"),
inverseJoinColumns = @JoinColumn(name = "course_id"))
private List<Course> courses;
//getter and setters
}
In the above code snippet, we have defined the entity class named Student has a many-to-many relationship with the course class and it indicated by the @ManyToMany annotation on the Student attribute.
Step 2: Define the Collection Attributes
Within the entity classes, we define the collection attributes to represent the relationships. The Student class, the course attribute represents the collection of the courses taken by the students.
Step 3: Map Collections Using Annotations
We use the JPA annotations to the map these collection attributes to the database.
Example: The @ManyToMany annotation is used to map the many to many relationships and the mappedBy attributes specifies the inverse side of the relationships.
Step 4: Configure the Fetch Type
We configure the fetch type for the collections using the fetch attributes of the @OneToMany or @ManyToMany annotations. The fetch type specifies whether the associated the entities should be eagerly or the lazily loaded from the database.
Step 5: Persistence Operations
Finally, we can perform the CRUD operations using the JPA APIs to the interact with the database.
JPA – Collection Mapping
In Java, JPA can defined as Java Persistence API. Collection Mapping is a powerful feature that allows developers to map relationships between the entities and collections in the database. It allows the developers to map the collections of the objects from Java to corresponding database structures.