Entity Inheritance
How to inherit properties from entity super classes.
ObjectBox - Entity Super Classes
Only available for Java/Kotlin at the moment
ObjectBox allows entity inheritance to share persisted properties in super classes. The base class can be an entity or non-entity class. For this purpose the @Entity
annotation is complemented by the @BaseEntity
annotation. There are three types of super classes, which are defined via annotations:
No annotation: The base class and its properties are not considered for persistence.
@BaseEntity: Properties are considered for persistence in sub classes, but the base class itself cannot be persisted.
@Entity: Properties are considered for persistence in sub classes, and the base class itself is a normally persisted entity.
For example:
The model for Sub, Sub_, will now include all properties: id
, baseString
and subString
.
It is also possible to inherit properties from another entity:
Notes on usage
It is possible to have classes in the inheritance chain that are not annotated with @BaseEntity. Their properties will be ignored and will not become part of the entity model.
It is not generally recommend to have a base entity class consisting of an ID property only. E.g. Java imposes an additional overhead to construct objects with a sub class.
Depending on your use case using interfaces may be more straightforward.
Restrictions
Superclasses annotated with @BaseEntity can not be part of a library.
There are no polymorphic queries (e.g. you cannot query for a base class and expect results from sub classes).
Currently any superclass, whether it is an @Entity or @BaseEntity, can not have any relations (like a ToOne or ToMany property).
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