Diskriminasi

Katrangan

Ing pawulangan sadurunge, sampeyan ndeleng Hibernate nggunakake kolom DTYPE VARCHAR khusus kanggo nyimpen jeneng kelas Entitas. Kolom kasebut diarani diskriminator . Iki digunakake kanggo nemtokake kelas sing bakal digawe kanggo baris tartamtu ing database.

Sampeyan bisa ngapusi kolom iki nganggo anotasi @DiscriminatorColumn . Tuladha:

@DiscriminatorColumn(name="column_name",   discriminatorType = DiscriminatorType.INTEGER)

Miturut spesifikasi JPA, diskriminator bisa duwe jinis ing ngisor iki:

• STRING
• CHAR
• ONGKO

Nanging, Hibernate ngidini sampeyan nggedhekake dhaptar iki rada. Ndhukung jinis Jawa iki: String, char, int, byte, short, boolean.

Yen kita nggunakake jinis INTEGER, banjur carane encode jeneng kelas Entitas ing? Kanggo iki, anotasi liyane digunakake - @DiscriminatorValue .

Deleng conto:

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="user_type",   discriminatorType = DiscriminatorType.INTEGER)
@Entity
class User {
  int id;
  String name;
  LocalDate birthday;
}

@Entity
@DiscriminatorValue("1")
class Employee extends User {
 	String occupation;
 	int salary;
 	LocalDate join;
}

@Entity
@DiscriminatorValue("2")
class Client extends User {
   String address;
}

Ing conto ing ndhuwur, kita marang Hibernate sing discriminator bakal nggunakake kolom user_type, kang bakal nyimpen nomer. Yen nyimpen nilai 1, tegese jinis baris yaiku Karyawan, yen 2 disimpen, banjur jinis baris kasebut Klien. Prasaja lan ayu.

@DiscriminatorValue

Nanging ora mung kuwi. Sampeyan bisa ngandhani Hibernate carane napsirake jinis senar nalika diskriminator kasebut NULL.

Iku bener banget prasaja. Sampeyan nemtokake nilai null kanggo @DiscriminatorValue anotasi . Contone, kaya iki:

@DiscriminatorValue("null")

Tuladha kelas:

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="user_type",   discriminatorType = DiscriminatorType.INTEGER)
@DiscriminatorValue("null")
@Entity
class User {
  int id;
  String name;
  LocalDate birthday;
}

Kita wis ngandhani Hibernate manawa saben baris tabel sing duwe NULL ing kolom user_type kudu diinterpretasikake minangka obyek saka jinis pangguna.

Nanging ora mung kuwi. Ana nilai liyane sing menarik kanggo anotasi @DiscriminatorValue.

Punika punika:

@DiscriminatorValue("not null")

Tuladha kelas:

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="user_type",   discriminatorType = DiscriminatorType.INTEGER)
@DiscriminatorValue("not null")
@Entity
class User {
  int id;
  String name;
  LocalDate birthday;
}

Kanthi anotasi iki, kita ngandhani Hibernate manawa saben baris tabel kanthi nilai non-NULL ing kolom user_type kudu diinterpretasikake minangka obyek saka jinis pangguna. Nanging iki mung kanggo cilik yen kelas ora ketemu sing wis nomer sing dibutuhake tegas kasebut.

Mangkene carane bisa digunakake kanggo macem-macem nilai diskriminator:

• 0 - nggawe obyek saka jinis Panganggo
• 1 - nggawe obyek saka jinis Employee
• 2 - nggawe obyek saka jinis Klien
• 3 - nggawe obyek saka jinis Panganggo
• 4 - nggawe obyek saka jinis Panganggo

@DiscriminatorFormula

Nanging ora mung kuwi. Kanggo discriminator kita, kita bisa nemtokake rumus integer sing bakal ngetung nilai kanggo anotasi @DiscriminatorValue .

Ana anotasi khusus kanggo iki, diarani @DiscriminatorFormula .

Tuladha:

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="user_type",   discriminatorType = DiscriminatorType.INTEGER)
@DiscriminatorFormula("case when ‘join’ is not null then 1 else 2 end")
@Entity
class User {
  int id;
  String name;
  LocalDate birthday;
}

@Entity
@DiscriminatorValue("1")
class Employee extends User {
 	String occupation;
 	int salary;
 	LocalDate join;
}

@Entity
@DiscriminatorValue("2")
class Client extends User {
   String address;
}

Nilai sing dibalekake dening @DiscriminatorFormula bakal dibandhingake karo Hibernate karo nilai sing ditemtokake ing anotasi @DiscriminatorValue . Kanthi, sampeyan bisa nulis skenario sing cukup rumit:

@DiscriminatorFormula(
           	"case when address is not null " +
           	"then 'Client' " +
           	"else (" +
           	"   case when occupation is not null " +
           	"   then 'Employee' " +
           	"   else 'Unknown' " +
           	"   end) " +
           	"end "
)