Tabel Gabungan

Katrangan

Strategi liyane kanggo nyimpen hirarki kelas ing basis data diarani Tabel Gabungan. Ana anotasi khusus kanggo iki:

@Inheritance(strategy = InheritanceType.JOINED)

Conto kelas kita:

@Inheritance(strategy = InheritanceType.JOINED)
@Entity
class User {
  int id;
  String name;
  LocalDate birthday;
}

@Entity
class Employee extends User {
 	String occupation;
 	int salary;
 	LocalDate join;
}

@Entity
class Client extends User {
   String address;
}

Nalika nggunakake anotasi iki, Hibernate bakal nyana tabel kapisah ing database kanggo saben kelas lan subclasses. Nalika milih data saka wong-wong mau, sampeyan kudu nggunakake operator SQL JOIN.

Contoh skema database:

CREATE TABLE user {
  id INT,
  name VARCHAR,
  birthday DATE
}

CREATE TABLE employee {
  id INT,
  occupation VARCHAR,
  salary INT,
  join DATE
}

CREATE TABLE client {
  id INT,
  address VARCHAR
}

Yen sampeyan arep njupuk data saka sawetara klien saka meja, banjur Hibernate kudu nggunakake JOIN kanggo nggabungake tabel:

SELECT u.id, u.name, u.birthday, c.address FROM user u JOIN client c ON u.id = c.id;

@PrimaryKeyJoinColumn

Kelas Entitas Anak duwe kolom ing tabel sing nuduhake id obyek saka kelas Entitas induk. Jeneng kolom iki minangka standar padha karo jeneng kolom kelas induk.

Tuladha:

@Inheritance(strategy = InheritanceType.JOINED)
@Entity
class User {
  @Id
  int user_identifier;
  String name;
  LocalDate birthday;
}

@Entity
class Employee extends User {
 	String occupation;
 	int salary;
 	LocalDate join;
}

@Entity
class Client extends User {
   String address;
}

Banjur tabel database bakal katon kaya iki:

CREATE TABLE user {
  user_identifier INT,
  name VARCHAR,
  birthday DATE
}

CREATE TABLE employee {
  user_identifier INT,
  occupation VARCHAR,
  salary INT,
  join DATE
}

CREATE TABLE client {
  user_identifier INT,
  address VARCHAR
}

Yen sampeyan pengin ngganti jeneng kolom ing tabel gumantung, sampeyan kudu nggunakake anotasi @PrimaryKeyJoinColumn . Tuladha:

@Inheritance(strategy = InheritanceType.JOINED)
@Entity
class User {
  @Id
  int user_identifier;
  String name;
  LocalDate birthday;
}

@Entity
@PrimaryKeyJoinColumn(name=”user_id”)
class Employee extends User {
 	String occupation;
 	int salary;
 	LocalDate join;
}

@Entity
@PrimaryKeyJoinColumn(name=”user_id2”)
class Client extends User {
   String address;
}

Banjur tabel database bakal katon kaya iki:

CREATE TABLE user {
  user_identifier INT,
  name VARCHAR,
  birthday DATE
}

CREATE TABLE employee {
  user_id INT,
  occupation VARCHAR,
  salary INT,
  join DATE
}

CREATE TABLE client {
  user_id2 INT,
  address VARCHAR
}