Annotation-based primary key settings for hibernate

Annotation-based hibernate primary key setting: @ ID.
So what are its generation rules? It is specified by @ generatedvalue.

Let's take a look at how it is defined:

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2. @ Target({Method, field })
4. @ Retention(Runtime)
6. Public @ InterfaceGeneratedvalue {
8. Generationtype strategy ()DefaultAuto;
10. String generator ()Default "";
12. }

 
@ Target ({method, field}) @ retention (runtime) Public @ interface generatedvalue {generationtype strategy () default auto; string generator () Default "";}
 

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1. Public EnumGenerationtype {
2. Table,
3. Sequence,
4. Identity,
5. Auto
6. }

 
Public Enum generationtype {table, sequence, identity, auto}
 

Now we can see that it provides four generation policies:
Table: uses a specific database table to store the sequence of identifiers.
Sequence: generate a serialization identifier.
Identity: The identifier is automatically generated by the database (mainly the automatic growth type)
Auto: hibernate automatically processes the generation of identifiers. It is not recommended for actual project development.
Note: When the primary key is int and the database is not automatically increasing, @ generatedvalue cannot work normally.

We can also use the following method to specify our primary key value:

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1. @ generatedvalue (generator = " C-assigned " )
2. @ genericgenerator (name = " C-assigned " , strategy = " assigned " )
3. private string employeeid;

@ Generatedvalue (generator = "C-assigned") @ genericgenerator (name = "C-assigned", strategy = "assigned") Private string employeeid;
 

Or do not define @ generatedvalue directly. The effect of defining only @ ID is the same.