About the primary key auto-increment field in hibernate

Error message:
Reference

Org. hibernate. id. IdentifierGenerationException: ids for this class must be manually assigned before calling save (): *** (POJO class, and persistence class name)

Analysis and Solution:

The id (primary key) type in the data table you want to operate on is set to "auto-increment type ".

In hibernate. cfg. xml, the id generation method is assigned, that is
Java code
<Id name = "id" type = "integer">
<Column name = "id"/>
<Generator class = "assigned"/>
</Id>

This kind of matching is contradictory!

The assigned generation method of the primary key is automatically used by the program to generate the primary key of the table. That is, the setId () method must be called in your test program.

You must specify the id before calling save () (or before calling save (), that is, the primary key value cannot be blank !).
The primary key generation method is changed to native, which is characterized by the ability to automatically select the primary key generation method based on the underlying database.