Skip to main content

Hibernate Features

@MappedSuperclass

This annotation can be used when you want to create inheritance in the Entities.

Entities may inherit from superclasses that contain persistent state and mapping information but are not entities. That is, the superclass is not decorated with the @Entity annotation and is not mapped as an entity by the Java Persistence provider. These superclasses are most often used when you have state and mapping information common to multiple entity classes.
Mapped superclasses are specified by decorating the class with the annotation javax.persistence.MappedSuperclass:
@MappedSuperclass
public class Employee {
    @Id
    protected Integer employeeId;
    ...
}
@Entity
public class FullTimeEmployee extends Employee {
    protected Integer salary;
    ...
}
@Entity
public class PartTimeEmployee extends Employee {
    protected Float hourlyWage;
    ...
}
Mapped superclasses cannot be queried and can’t be used in EntityManager or Query operations. You must use entity subclasses of the mapped superclass in EntityManager or Query operations. Mapped superclasses can’t be targets of entity relationships. Mapped superclasses can be abstract or concrete.
Mapped superclasses do not have any corresponding tables in the underlying datastore. Entities that inherit from the mapped superclass define the table mappings. For instance, in the preceding code sample, the underlying tables would be FULLTIMEEMPLOYEE and PARTTIMEEMPLOYEE, but there is no EMPLOYEE table.

Non-Entity Superclasses

Entities may have non-entity superclasses, and these superclasses can be either abstract or concrete. The state of non-entity superclasses is nonpersistent, and any state inherited from the non-entity superclass by an entity class is nonpersistent. Non-entity superclasses may not be used in EntityManager or Query operations. Any mapping or relationship annotations in non-entity superclasses are ignored.

Ref: https://docs.oracle.com/javaee/6/tutorial/doc/bnbqn.html

Comments

Popular posts from this blog

Patterns Knowledge

Anti Pattern: Its a pattern which we repeatedly do and which brings negative results. Architecture by implication: Systems lacking a clear and document architecture. Cover Your Assets: Continuing to document and present alternatives, without ever making an architectural decision. Witches Brew: Architectures made by groups resulting in a mix of ideas and lack a clear vision. Gold Plating: Continuing to define an architecture well pass the time which results in no benefits to the architecture. Vendor King: A product dependent architectures leading to a loss of control of architecture and development costs Big Bang Architecture: Designing the entire architecture at the beginning of the project when you know the least about the system.

Some good links

https://www.html5rocks.com/en/tutorials/internals/howbrowserswork/ http://taligarsiel.com/ClientSidePerformance.html -- Client side performance tips https://ariya.io/ https://vertx.io/docs/ -- New exciting Framework, Must read. https://javaee.github.io/ -- Very good resource to see various javaee projects and explore enterprise architecture and design concepts. https://projects.eclipse.org/projects/ee4j -- Lots of interesting open source projects by eclipse http://openjdk.java.net/projects/mlvm/ -- the main project for supporting more dynamic languages to jvm. http://esprima.org/ -- EcmaScript parser http://c2.com/ppr/ and http://hillside.net/ -- Good place to learn patterns http://cr.openjdk.java.net/~briangoetz/lambda/Defender%20Methods%20v4.pdf https://validator.w3.org/nu/ -- This will validate your website css and js https://www.cellstream.com/intranet/reference-reading/faq/216-what-is-2-128.html http://shattered.io/ -- An example of SHA1 collision attack.

@MappedSuperclass vs. @Inheritance

MappedSuperClass must be used to inherit properties, associations, and methods. Entity inheritance must be used when you have an entity, and several sub-entities. You can tell if you need one or the other by answering this questions: is there some other entity in the model which could have an association with the base class? If yes, then the base class is in fact an entity, and you should use entity inheritance. If no, then the base class is in fact a class that contains attributes and methods that are common to several unrelated entities, and you should use a mapped superclass. For example: You can have several kinds of messages: SMS messages, email messages, or phone messages. And a person has a list of messages. You can also have a reminder linked to a message, regardless of the kind of message. In this case, Message is clearly an entity, and entity inheritance must be used. All your domain objects could have a creation date, modification date and ID, and you could thus