Hibernate Inheritance Mapping

Inheritance

MappedSuperclass

Totally separated tables in database. Two tables will be created for DebitAccount and CreditAccount. No fetching against subclass is available.

@MappedSuperclass

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

…

}

@Entity(name = "CreditAccount")

public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

…

}

Single Table (default choice for JPA)

Each subclass in a hierarchy must define a unique discriminator value, which is used to differentiate between rows belonging to separate subclass types. If this is not specified, the DTYPE column is used as a discriminator, storing the associated subclass name.

@Entity(name = "Account")

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

…

}

@Entity(name = "CreditAccount")

public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

…

}

@Entity(name = "Account")

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)

@DiscriminatorFormula(

    "case when debitKey is not null " +

    "then 'Debit' " +

    "else ( " +

    "   case when creditKey is not null " +

    "   then 'Credit' " +

    "   else 'Unknown' " +

    "   end ) " +

    "end "

)

//@DiscriminatorColumn(

//    name="type",

//    discriminatorType=DiscriminatorType.STRING)

// only STRING, CHAR, INTEGER are valid

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

@DiscriminatorValue(value = "Debit")

public static class DebitAccount extends Account {

    private String debitKey;

…

}

@Entity(name = "CreditAccount")

@DiscriminatorValue(value = "Credit")

public static class CreditAccount extends Account {

    private String creditKey;

…

}

@Entity(name = "Account")

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)

@DiscriminatorValue( "null" )

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

@DiscriminatorValue( "Debit" )

public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

…

}

@Entity(name = "CreditAccount")

@DiscriminatorValue( "Credit" )

public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

…

}

@Entity(name = "OtherAccount")

@DiscriminatorValue( "not null" )

public static class OtherAccount extends Account {

    private boolean active;

…

}

Joined Table

Tables for subclasses will have a foreign key column that points back to superclass.

@Entity(name = "Account")

@Inheritance(strategy = InheritanceType.JOINED)

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

…

}

@Entity(name = "CreditAccount")

public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

…

}

@Entity(name = "Account")

@Inheritance(strategy = InheritanceType.JOINED)

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

@PrimaryKeyJoinColumn(name = "account_id")

public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

…

}

@Entity(name = "CreditAccount")

@PrimaryKeyJoinColumn(name = "account_id")

public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

…

}

Table per (concrete) class

@Entity(name = "Account")

@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)

public static class Account {

    @Id

    private Long id;

…

}

@Entity(name = "DebitAccount")

public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

…

}

@Entity(name = "CreditAccount")

public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

…

}

Immutable

Hibernate skips any updates if the @Immutable has been used.

@Entity(name = "Batch")

public static class Batch {

    @Id

    private Long id;

    private String name;

    @OneToMany(cascade = CascadeType.ALL)

    @Immutable

    private List<Event> events = new ArrayList<>( );

    //Getters and setters are omitted for brevity

}

@Entity(name = "Event")

@Immutable

public static class Event {

    @Id

    private Long id;

    private Date createdOn;

    private String message;

    //Getters and setters are omitted for brevity

}