Скачать или смотреть Lesson - 21 : Hibernate - Generators classes using XML and Annotation based Configuration

1. For a new object, before an object is going to be stored in a database, id for that object is mandatory because hibernate checks whether already another object with the same id is exist in the database or not (table or not) using the id of the new object.
2. If already another object exist with the same id in database then hibernate throws an exception.
3. In hibernate for an object we can manually assign the value for id or we can use predefined id generators technique given by hibernate for generating id of the object.
4. We need to inform the hibernate that whether a developer is going to assign the id or it should be generated by hibernate using ＜generator ＞ tag under ＜id＞ tag of mapping file or hbm file.
5. Hibernate has provided some predefined id generators techniques for generating id. If the existing id generation techniques are not suitable for our application then we can also create our own in id generators technique. This is called custom id generators.
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1. Assigned generator : It is the default id generator class or technique.
2. Increment generator : This generator class uses max(id)+1 formula for generating an id for a new object, before it is going to be stored in a database.
3. Sequence generator : This generator class reads a next value of a given sequence from a database and then assigns that value for id and then the object will be inserted into database.
4. Hilo generator : This generator class generates id for an object when first time used as one(1) From second time onwards, the id will be generated using max_lo*next_hi+next_hi
5. Identity generator : This generator class is used to inform that id column of the databse table is a auto increment column of the table.
6. Native generator : This generator class is not a new formula for generating ids.
7. Foreign generator : This generator class is only applicable in one to one relationship between objects.
8. Uuid.hex generator : All the above generators classes are applicable for number type of primary key column of table.


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