Sequencia chave primaria - MYSQL

Oi Melqui,

Sequence é suportada apenas em alguns bancos de dados, como Oracle e Postgres.

No caso do MySQL o Hibernate acabou utilizando esse esquema de ter um id global para todas as tabelas. Se isso for um problema para você, o recomendado é utilizar a estratégia IDENTITY mesmo.

Bons estudos!

Professor coloquei identity, e tentei cadastrar produto com categoria novamente, classe: na categoria também, porém veio o seguinte erro:

Hibernate: 
    insert 
    into
        categorias
        (nome) 
    values
        (?)
nov. 09, 2021 3:01:14 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
WARN: SQL Error: 1364, SQLState: HY000
nov. 09, 2021 3:01:14 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Field 'id' doesn't have a default value
Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not execute statement
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:154)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:181)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:188)
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:726)
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:706)
    at br.com.alura.loja.dao.CategoriaDAO.cadastrar(CategoriaDAO.java:16)
    at br.com.alura.loja.testes.CadastroDeProduto.main(CadastroDeProduto.java:26)
Caused by: org.hibernate.exception.GenericJDBCException: could not execute statement
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:47)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:113)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:99)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:200)
    at org.hibernate.dialect.identity.GetGeneratedKeysDelegate.executeAndExtract(GetGeneratedKeysDelegate.java:57)
    at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:43)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3200)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3806)
    at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:84)
    at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:645)
    at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:282)
    at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:263)
    at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:317)
    at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:330)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:287)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:193)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:123)
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:185)
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:128)
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:55)
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:102)
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:720)
    ... 3 more
Caused by: java.sql.SQLException: Field 'id' doesn't have a default value
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1092)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1040)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeLargeUpdate(ClientPreparedStatement.java:1347)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdate(ClientPreparedStatement.java:1025)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:197)
    ... 21 more

Como as suas tabelas já estavam criadas, você vai precisar dropar, pois elas foram criadas anteriormente pelo Hibernate com a estrategia de SEQUENCE.

Funcionou! Obrigado professor.