4.2.1.1. Base Entity Classes

The base entity classes and interfaces are described in detail in this section.

EntityClasses

  • Instance – declares the basic methods for working with objects of application domain:

    • getting references to the object meta-class;

    • generating the instance name;

    • reading/writing attribute values by name;

    • adding listeners receiving notifications about attribute changes.

  • Entity – extends Instance with entity identifier; at the same time Entity does not define the type of the identifier leaving this option to descendants.

  • AbstractInstance – implements the logic of working with attribute change listeners.

    Warning

    AbstractInstance stores the listeners in WeakReference, and if there are no external references to the added listener, it will be immediately destroyed by garbage collector. Normally, attribute change listeners are visual components and UI datasources that are always referenced by other objects, so there is no problem with listeners dropout. However, if a listener is created by application code and no objects refer to it in a natural way, it is necessary to save it in a certain object field apart from just adding it to Instance.

  • AbstractNotPersistentEntity – base class of non-persistent entities.

  • BaseGenericIdEntity – base class of persistent entities. It implements Entity but does not specify the type of the identifier (i.e. the primary key) of the entity.

  • EmbeddableEntity - base class of embeddable persistent entities.

Below we consider base classes recommended for inheriting your entities from.

StandardEntity

Inherit from StandardEntity if you want a standard set of features: the primary key of UUID type, the instances have information on who and when created and modified them, require optimistic locking and soft deletion.

EntityClasses Standard

  • HasUuid – interface for entities having a globally unique identifier.

  • Versioned – interface for entities supporting optimistic locking.

  • Creatable – interface for entities that keep the information about when and by whom the instance was created.

  • Updatable – interface for entities that keep the information about when and by whom the instance was last changed.

  • SoftDelete – interface for entities supporting soft deletion.

BaseUuidEntity

Inherit from BaseUuidEntity if you want an entity with the primary key of UUID type but you don’t need all features of StandardEntity. You can implement some of the interfaces Creatable, Versioned, etc. in your concrete entity class.

EntityClasses Uuid
BaseLongIdEntity

Inherit from BaseLongIdEntity or BaseIntegerIdEntity if you want an entity with the primary key of the Long or Integer type. You can implement some of the interfaces Creatable, Versioned, etc. in your concrete entity class. Implementing HasUuid is highly recommended, as it enables some optimizations and allows you to identify your instances uniquely in a distributed environment.

EntityClasses Long
BaseStringIdEntity

Inherit from BaseStringIdEntity if you want an entity with the primary key of the String type. You can implement some of the interfaces Creatable, Versioned, etc. in your concrete entity class. Implementing HasUuid is highly recommended, as it enables some optimizations and allows you to identify your instances uniquely in a distributed environment. The concrete entity class must have a string field annotated with the @Id JPA annotation.

EntityClasses String
BaseIdentityIdEntity

Inherit from BaseIdentityIdEntity if you need to map the entity to a table with IDENTITY primary key. You can implement some of the interfaces Creatable, Versioned, etc. in your concrete entity class. Implementing HasUuid is highly recommended, as it enables some optimizations and allows you to identify your instances uniquely in a distributed environment. The id attribute of the entity (i.e. getId/setId methods) will be of type IdProxy which is designed to substitute the real identifier until it is generated by the database on insert.

EntityClasses Identity
BaseGenericIdEntity

Inherit from BaseGenericIdEntity directly if you need to map the entity to a table with a composite key. In this case, the concrete entity class must have a field of the embeddable type representing the key, annotated with the @EmbeddedId JPA annotation.