Inheritence

Abstract Entity

Abstract class can be annotated @Entity;

• like concrete entity,

• cannot be instantiated,

• can be queried

Mapped Superclass

@MappedSuperclass - contains mapping information but

• not persisted entity

• cannot be queried

• must use sub-class, not this (super) class

• cannot be target of relationship

• has no corresponding table in db

Mapping Strategies

@Inheritence (strategy = ) on root class

• SINGLE_TABLE

  • default

  • has discriminatory column to tell subclass

  • @DiscriminatoryColumn (study further...)

• TABLE_PER_CLASS

  • support is optional (not all server supports this)

  • poor on polymorphic relationships

• JOIN - table for parent class joins table for children

  • may lead to poor performance