What are the three types of Inheritance Mapping Strategies described in JPA?JPA Interview Questions for Freshers/JPA Interview Questions and Answers for Freshers & Experienced

What are the three types of Inheritance Mapping Strategies described in JPA?

JPA describes three inheritance mapping strategies (Inheritance Mapping Strategies), that is, how JPA will work with the classes derived from the Entity:

1) one table for the entire inheritance hierarchy ( a single table per class hierarchy ) – all enity one table, to identify the type of entity is determined by a special column “discriminator column” . For example, if there is an entity Animals with the descendant classes Cats and Dogs, with such a strategy, all entities are recorded in the Animals table, but they have an additional column, animalType, in which the value “cat” or “dog” is written respectively. Minusis that in the general table, all fields unique for each of the descendant classes will be created, which will be empty for all other descendant classes. For example, in the table of animals there will be the speed of climbing a tree from cats and whether the dog can bring sneakers from dogs, which will always be null for a dog and cat, respectively.

2) unifying strategy ( joined subclass strategy ) – in this strategy, each enity class stores data in its own table, but only unique columns (not inherited from ancestor classes) and the primary key, and all inherited columns are written to ancestor class tables a relationship is established between these tables, for example, in the case of the Animals classes (see above), there will be three tables of animals, cats, dogs, and only the key and speed of climbing will be recorded in cats, in dogs – the key and whether the dog can bring a stick , and in animals all the rest of the data of cats and dogs are c links th to the appropriate table. The downside is the performance loss from joining tables (join) for any operations.

3) one table for each class ( table per concrete class strategy ) – everything is simple here every individual class of successor has its own table, i.e. for cats and dogs (see above), all data will be recorded simply in the tables cats and dogs as if they did not have a common superclass at all. The downside is poor support for polymorphism (polymorphic relationships) and the fact that selecting all the classes in the hierarchy will require a large number of separate sql queries or using a UNION query.

Posted Date:- 2021-11-08 16:35:18