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What is discriminator 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.
What is discriminator in Java?
Annotation Type DiscriminatorValue
If the DiscriminatorValue annotation is not specified and a discriminator column is used, a provider-specific function will be used to generate a value representing the entity type. If the DiscriminatorType is STRING , the discriminator value default is the entity name.
@DiscriminatorFormular – Modeling Single Table Inheritance Without a Discriminator
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What is discriminator 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.
When would you use a discriminator?
Discriminator is commonly used in SINGLE_TABLE inheritance because you need a column to identify the type of the record. Example: You have a class Student and 2 sub-classes: GoodStudent and BadStudent.
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.
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 MappedSuperclass in JPA?
JPA – Mapped Superclasses. A quick overview of JPA Mapped Superclasses. 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.
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What is JPA inheritance?
JPA Inheritence Overview
Inheritence is a key feature of object-oriented programming language in which a child class can acquire the properties of its parent class. This feature enhances reusability of the code. The relational database doesn’t support the mechanism of inheritance.
What is JPA?
The Java Persistence API (JPA) is a specification of Java. It is used to persist data between Java object and relational database. JPA acts as a bridge between object-oriented domain models and relational database systems. As JPA is just a specification, it doesn’t perform any operation by itself.
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.
Hibernate Tip: SINGLE_TABLE strategy without discriminator column
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What is SQL discriminator?
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 are JPA implementations?
The reference implementation of JPA is EclipseLink. JPA permits the developer to work directly with objects rather than with SQL statements. The JPA implementation is typically called persistence provider. The mapping between Java objects and database tables is defined via persistence metadata.
What is a discriminator in databases?
Discriminators in DBMS
The discriminator of a weak entity set is a set of attributes that differentiates it. In the above example, the collection of sec_id, semester and year put together is called ‘discriminator’. The discriminator is also called a ‘partial key’.
What is a discriminator in class?
The least-derived mapped class in an inheritance hierarchy defines the discriminator.
What are the types of inheritance mapping in JPA?
JPA defines three inheritance strategies namely, SINGLE_TABLE , TABLE_PER_CLASS and JOINED .
Can the entity class inherit from non entity classes?
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.
What is @primarykeyjoincolumn?
It is used to join the primary table of an entity subclass in the JOINED mapping strategy to the primary table of its superclass; it is used within a SecondaryTable annotation to join a secondary table to a primary table; and it may be used in a OneToOne mapping in which the primary key of the referencing entity is …
How does Hibernate inheritance work?
@Inheritance – It is used to define the type of inheritance used in hibernate and it is defined in the parent class. If the Inheritance annotation is not specified or if no inheritance type is specified for an entity class hierarchy, the SINGLE_TABLE mapping strategy is used.
What is @version in JPA?
Version used to ensure that only one update in a time. JPA provider will check the version, if the expected version already increase then someone else already update the entity so an exception will be thrown.
learn inheritance in hibernate like a pro || table per class hierarchy in hibernate || STEP BY STEP
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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.
What is @CreationTimestamp?
Annotation Type CreationTimestamp
Marks a property as the creation timestamp of the containing entity. The property value will be set to the current VM date exactly once when saving the owning entity for the first time.
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