Hibernate inheritance mapping (simple inheritance, subclass,joined-subclass,union-subclass)

Inheritance Mappings

Demand:

Parent class: Animal sub-category: Cat Monkey

Simple Inheritance mappings (3 tables, 3 mapping files) (how many subclasses, how many mapping files are written)

Inheritance mapping using subclass (one table, 1 mapping files)

Inheritance mapping using Joined-subclass (3 tables, 1 mapping files)

Using Union-subclass Inheritance Mappings (2 tables, 1 mapping files) recommended

Simple Inheritance Mappings

Simple inheritance mappings, how many subclasses, how many mapping files are written.
Step one: Establish the inheritance relationship of the animal class and Cat class

Step Two: Configure the Cat.hbm.xml mapping file

Step three: Add data to the table to test

After running the console display with the database results:

Step four: Let's try to get the data from the database, respectively, by subclass and parent class.

Inheritance Mappings

Needs: cats, monkeys, animals.

Method 1: Use subclass to map all subclasses to a single table (1 tables)

What's the use of. Subclasses teach much, and subclasses are simpler, that is, there are only individual attributes.

Benefit: Because a mapping file is used, the number of mapping files is reduced. Cons: (not conforming to database design principles) A mapping file: Animal.hbm.xml

Note To add the discriminator discriminator to the zone molecule class

Step one: Establish an inheritance relationship with animal, Cat Monkey class

Step Two: Configure the relevant mapping file (only configure Animal.hbm.xml here)

Step three: Add data to the table and test it.

Run the test a bit ~

Discriminator does not set the class type, default is the full name of the class

Let's specify the type of discriminator.

Method 2: Map each class to the corresponding table (3 tables) by Joined-subclass

A mapping file that stores all subclasses, and the parent classes of subclasses are the corresponding tables;

Disadvantage: The table structure is more complex, inserting a subclass of information, you need 2 sql: Insert to the parent class, insert into the child class. Step one: Establish the animal,cat of the inheritance relationship, Monkey class (IBID., omitted here) Step two: Configure the associated mapping file (same Animal.hbm.xml)
Step three: Establish the test file (IBID., omitted here) then we run the test:




Method 3: (recommended) map each subclass to a table by Union-subclass, parent class does not correspond to table (2 tables) Step One: Establish the animal,cat of the inheritance relationship, Monkey class (IBID., omitted here) Step Two: Configure the associated mapping file (same Animal.hbm.xml)

Step three: Establish the test file (IBID., omitted here) then we run the test:

Because the data operation does not use the animal table, we set it up without generating the animal table