What is the use of discriminator column in hibernate?

In case of table per class hierarchy an discriminator column is added by the hibernate framework that specifies the type of the record. It is mainly used to distinguish the record. To specify this, discriminator subelement of class must be specified. The subclass subelement of class, specifies the subclass.

What is discriminator column in JPA?

The discriminator column is always in the table of the base entity. It holds a different value for records of each class, allowing the JPA runtime to determine what class of object each row represents. The DiscriminatorColumn annotation represents a discriminator column.

Is a mapping requires discriminator column?

The SINGLE_TABLE strategy maps records from the same database table to different entity classes of an inheritance hierarchy. If you want to use this strategy with JPA, your database table needs to have a discriminator column. The value in this column identifies the entity class to which each record shall be mapped.

What is DiscriminatorValue?

Annotation Type DiscriminatorValue Specifies the value of the discriminator column for entities of the given type. The DiscriminatorValue annotation can only be specified on a concrete entity class.

Which persistent strategy uses the discriminator attribute?

The javax. persistence. DiscriminatorValue annotation may be used to set the value entered into the discriminator column for each entity in a class hierarchy. You may decorate only concrete entity classes with @DiscriminatorValue.

What is the use of @MappedSuperclass?

A mapped superclass provides persistent entity state and mapping information but is not itself an entity. A mapped superclass, unlike an entity, does not allow querying, persisting, or relationships to the superclass. @MappedSuperclass annotation is used to designate a class as mapped superclass.

Does Hibernate use setters?

As others have mentioned, if you annotate a property getter method, then Hibernate uses the setter when reading values from the database. Basically, Hibernate assumes that anything that it is writing to the database will eventually need to be read from the database.

Which inheritance mapping strategy uses discriminator column?

Single Table Inheritance. Single Table Inheritance is an inheritance mapping strategy where all classes of a hierarchy are mapped to a single database table. In order to distinguish which row represents which type in the hierarchy a so-called discriminator column is used.

What is discriminator column SQL?

The discriminator column itself is used to distinguish between different classes when class hierarchies are mapped flat or vertical. The idea behind the flat and vertical mapping is that every class is mapped into a single row in the base class table. The discriminator value is used to define the type of each row.

What is a discriminator in class?

The least-derived mapped class in an inheritance hierarchy defines the discriminator.

What is @MappedSuperclass in Hibernate?

According to the Hibernate docs, MappedSuperclass allows mapping inheritance, where the super class is not treated as an entity, and where polymorphic queries that fetch objects by the base class are not supported.

Does Hibernate require getters and setters?

Although Hibernate does not require it, it is recommended to follow JavaBean conventions by defining getters and setters for you entities persistent attributes. You can still tell Hibernate to directly access the entity’s fields.

Do JPA entities need setters?

With JPA, the default constructor is required, however, you are not required to use setters. You can choose a property access strategy(field or method) based on where you place the annotations.

What kind of mapping is preferred for Hibernate inheritance mapping?

Hibernate supports the three basic inheritance mapping strategies: table per class hierarchy. table per subclass. table per concrete class.

How do I add a discriminator in SQL?

You can specify the discriminator value for each sub-class.

  1. Right click on each of the corresponding sub-classes for adding discriminator. Select ORM > ORM Class Detail… from the popup menu.
  2. In the Class Specification window, enter the discriminator value that represent the sub-class.
  3. Click OK to confirm the change.

What is the output of discriminator?

The discriminator output is just a number (not an array)’ whereas the loss is always a scalar value. When we compute mean square error of two images it is also a scalar value.

What is a discriminator field in database?

What is the difference between @entity and @table in Hibernate?

Entity means the class which you will use in your program and Table means the actual Database table that you will access through your program. Hibernate being an ORM requires you to declare the relationship between the tables and the classes mapping to them.