MappedSuperclass

A class designated with the MappedSuperclass annotation can be mapped in the same way as an entity except that the mappings will apply only to its subclasses since no table exists for the mapped superclass itself. When applied to the subclasses the inherited mappings will apply in the context of the subclass tables. Mapping information may be overridden in such subclasses by using the {@link AttributeOverride} and {@link AssociationOverride} annotations or corresponding XML elements.

Example: Concrete class as a mapped superclass

@MappedSuperclass
public class Employee {

@Id protected Integer empId;
@Version protected Integer version;
@ManyToOne @JoinColumn(name="ADDR")
protected Address address;

public Integer getEmpId() { ... }
public void setEmpId(Integer id) { ... }
public Address getAddress() { ... }
public void setAddress(Address addr) { ... }
}

// Default table is FTEMPLOYEE table
@Entity
public class FTEmployee extends Employee {

// Inherited empId field mapped to FTEMPLOYEE.EMPID
// Inherited version field mapped to FTEMPLOYEE.VERSION
// Inherited address field mapped to FTEMPLOYEE.ADDR fk


// Defaults to FTEMPLOYEE.SALARY

protected Integer salary;


public FTEmployee() {}


public Integer getSalary() { ... }

public void setSalary(Integer salary) { ... }
}

@Entity @Table(name="PT_EMP")
@AssociationOverride(name="address",


joincolumns=@JoinColumn(name="ADDR_ID"))
public class PartTimeEmployee extends Employee {

// Inherited empId field mapped to PT_EMP.EMPID
// Inherited version field mapped to PT_EMP.VERSION
// address field mapping overridden to PT_EMP.ADDR_ID fk
@Column(name="WAGE")
protected Float hourlyWage;

public PartTimeEmployee() {}

public Float getHourlyWage() { ... }
public void setHourlyWage(Float wage) { ... }
}

Example: Non-entity superclass

public class Cart {

// This state is transient
Integer operationCount;

public Cart() { operationCount = 0; }
public Integer getOperationCount() { return operationCount; }
public void incrementOperationCount() { operationCount++; }
}

@Entity
public class ShoppingCart extends Cart {

Collection items = new Vector();

public ShoppingCart() { super(); }


...

@OneToMany
public Collection getItems() { return items; }
public void addItem(Item item) {
items.add(item);
incrementOperationCount();
}
}