jpa.md

Tips for usage with JPA

Based on the spec here

1. Declare your JPA classes as non-sealed.

Because this processor generates a sealed abstract class, Java requires that you explicitly decide whether any extending class is final, sealed, or non-sealed.

The correct choice when making a JPA entity is non-sealed

2. Do not generate equals or hashCode

You won't be able to do that without making your class final, which goes afoul of the rule above, but also a "proper" equals and hashCode implementation for a JPA entity should not be based on the fields of said entity.

For more information, consult those more experienced in this

3. Make fields be package-private and don't access them directly

One of the limitations of this processor is that none of the fields can be made private. You should still make fields package private and follow the convention of accessing them only through the getters.

4. Be careful when generating toString

There are some caveats with making a toString for an entity. Make sure to read up here.

Likely you will want to write this yourself or not write one at all.

5. Override methods as needed.

In some contexts, you might want to have a different implementation for a getter or a setter. In these cases, you should simply @Override the method in the generated superclass.

Full example

import javax.persistence.*;
import java.util.Objects;

import dev.mccue.magicbean.MagicBean;

@Entity
@Table(name = "employees")
@MagicBean
public non-sealed class Employee extends EmployeeBeanOps {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    Long id;

    @Column(name = "first_name")
    String firstName;

    @Column(name = "last_name")
    String lastName;

    @Column(name = "department")
    String department;

    @Column(name = "email")
    String email;

    @Column(name = "salary")
    String salary;

    @OneToMany(cascade ={CascadeType.REMOVE}, orphanRemoval = true, mappedBy = "client")
    Collection<ClientAttributeEntity> attributes;
    
    @Override
    public Collection<ClientAttributeEntity> getAttributes() {
        if (attributes == null) {
            attributes = new LinkedList<>();
        }
        return attributes;
    }

    public Employee() {

    }

    public Employee(String firstName, String lastName, String department, String email, String salary) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.department = department;
        this.email = email;
        this.salary = salary;
    }
    
    @Override
    public boolean equals(Object o) {
        if (!(o instanceof ClientEntity that)) {
            return false;
        }
        else {
            return Objects.equals(this.id, that.getId());
        }
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(this.id);
    }
}