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
}
