spring-data-jpa

Spring Data JPA Patterns

Entity design

@Entity
@Table(name = "users", indexes = {
    @Index(name = "idx_users_email", columnList = "email", unique = true)
})
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true, length = 255)
    private String email;

    @Column(nullable = false)
    private String passwordHash;

    @Enumerated(EnumType.STRING)
    @Column(nullable = false, length = 50)
    private Role role;

    @CreationTimestamp
    @Column(updatable = false)
    private Instant createdAt;

    @UpdateTimestamp
    private Instant updatedAt;

    @Version
    private Long version;                   // Optimistic locking

    protected User() {}                     // JPA requires no-arg constructor

    public User(String email, String passwordHash, Role role) {
        this.email = Objects.requireNonNull(email);
        this.passwordHash = Objects.requireNonNull(passwordHash);
        this.role = Objects.requireNonNull(role);
    }

    // Getters only — no public setters; mutate via domain methods
    public Long id() { return id; }
    public String getEmail() { return email; }
    public Role getRole() { return role; }
    public Instant getCreatedAt() { return createdAt; }

    public void changeEmail(String newEmail) {
        this.email = Objects.requireNonNull(newEmail);
    }
}

ID strategy: Use IDENTITY for single-node deployments (PostgreSQL, MySQL sequences). Use SEQUENCE with a named sequence for batch inserts (avoids INSERT per row). Avoid AUTO — it behaves inconsistently across databases.

No public setters on entities. Expose domain methods (changeEmail, deactivate, addItem) to enforce invariants. JPA requires a no-arg constructor — mark it protected so it is not called outside the framework.

Audit timestamps: @CreationTimestamp and @UpdateTimestamp (Hibernate) or @EntityListeners(AuditingEntityListener.class) + @CreatedDate / @LastModifiedDate (Spring Data Auditing). Prefer Instant for UTC storage.