com.anasoft.os.daofusion.entity
Interface Persistable<ID extends java.io.Serializable>

Type Parameters:

ID - Java type of the primary key column.

All Superinterfaces:

java.io.Serializable

All Known Implementing Classes:

BitemporalWrapper, ImmutablePersistentEntity, MutablePersistentEntity, PersistentEntity, PersistentEnumeration

public interface Persistable<ID extends java.io.Serializable>
extends java.io.Serializable

Generic persistent entity contract used by the PersistentEntityDao.

Implementations of this interface must follow some general rules regarding JPA object-relational mapping concepts:

• Each persistent entity must specify database identity field(s) which will be reflected as primary key(s) within the underlying database table. There are basically two ways to manage the database identity:
  • simple primary key approach - use the Id annotation to mark a single id field to be used as the primary key. It is common to mark the id field using the GeneratedValue annotation as well in case the identifier should be automatically assigned upon persistent entity creation.
  • composite primary key approach - use the Embeddable annotation to mark the primary key class and join it with the persistent entity using IdClass and Id annotations. In case of necessary primary key field association overrides, it is advised to use Embeddable and EmbeddedId annotations instead.
• Mutable persistent entities should use the Version annotation to mark an optimistic lock value (version) field. This way, the underlying persistence provider is able to enforce optimistic locking strategy on the persistent entity.
• Each persistent entity must provide a reliable Object.hashCode() and Object.equals(Object) implementation which covers all possible entity states.

There are basically two approaches to implementing Object.hashCode() and Object.equals(Object) methods:

• business key approach - set of "semi"-unique attributes that uniquely describe the persistent entity as a whole (this attribute combination is unique for each persistent entity instance). However, this imposes certain limitations on attributes within the set which could potentionally break the Object.hashCode() and Object.equals(Object) method contract (for example, uniqueness might be broken if any of the "semi"-unique attributes change, persistent entity instance has to have all "semi"-unique attributes set in advance for Object.hashCode() and Object.equals(Object) to work properly, etc.).
• synthetic generated value approach - generate a globally-unique identifier value and assign it to the oid field upon the persistent entity instance creation. The oid field serves as an object identity, allowing the entity to be contained within collections and properly handled between multiple persistence sessions. This approach essentially tries to separate the object identity and object value concepts from each other (unlike the business key approach which combines them together).

As for the inheritance mapping strategy, it is up to the user to mark specific root nodes within the persistent entity hierarchy via the Inheritance annotation as appropriate. Keep in mind that the default JPA inheritance strategy is set to InheritanceType.SINGLE_TABLE along with its implications on the underlying database schema.

Author:

vojtech.szocs

See Also:

PersistentEntityDao