Sam-Kruglov

/**
 * Defines common Id Generator that use PostgreSQL sequences properly.
 * It uses a separate sequence for the chosen ID, as opposed to using a single sequence for all IDs;
 * the same result can be achieved by simply using {@code @GeneratedValue(strategy = GenerationType.IDENTITY)}, but
 * that way hibernate would use a sequence as an identity, which would decrease performance.
 * <p>
 * Generates a sequence for each entity "entityName_seq"
 */
@GenericGenerator(name = "SequencePerEntityGenerator", strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator",
        parameters = @Parameter(name = "prefer_sequence_per_entity", value = "true"))

Sam-Kruglov

@Entity
@Table(name = "users")
public class User implements Identifiable<Long> {
    
    @Id
    @GeneratedValue(generator = "SequencePerEntityGenerator")
    private Long id; // only getter
    
    @Column(length = 16, nullable = false, unique = true)
    private String username; // getter and setter

Sam-Kruglov

@Entity
@Table(name = "groups")
public class Group implements Identifiable<Long> {
    
    @Id
    @GeneratedValue(generator = "SequencePerEntityGenerator")
    private Long id; // getter
    
    @Column(nullable = false, unique = true)
    private String name; // getter and setter

Sam-Kruglov

public interface UserRepository extends CrudRepository<User, Long> {}

Sam-Kruglov

public interface GroupRepository extends CrudRepository<Group, Long> {}

Sam-Kruglov

{
  "_links" : {
    "groups" : {
      "href" : "http://localhost:8080/groups"
    },
    "users" : {
      "href" : "http://localhost:8080/users"
    },
    "profile" : {
      "href" : "http://localhost:8080/profile"

Sam-Kruglov

{
  "name": "A",
  "_links": {
    "self": {
      "href": "http://localhost:8080/groups/1"
    },
    "group": {
      "href": "http://localhost:8080/groups/1"
    },
    "users": {

Sam-Kruglov

/**
 * Only defines a {@link com.samkruglov.entities.User#username username}.
 */
public class UserUsername {
    
    private final String username; // getter & consctuctor
        
    // equals & hashcode
}

Sam-Kruglov

public interface UserRepository extends CrudRepository<User, Long> {
    
    @RestResource(path = "username", rel = "getUsername")
    UserUsername findUsernameById(@Param("id") Long id);
}

Sam-Kruglov

{
    "username": "jsmith"
}