Problem with SQLStorage

How do to save the "id field" in a MySQL database table?? Always it has a NULL
value!!! I tried to redefine the "ID field"in a archetype:

schema=Schema((
 
    StringField('id',
                required=1, 
                searchable=1,
                storage=MySQLSQLStorage(),
                widget=StringWidget(label_msgid="label_name",
                                description_msgid="help_name",
                                i18n_domain="quercus1"),
                ),
      
    StringField('dni',
        required=1,
        searchable=1,
        storage=MySQLSQLStorage(),
        widget=StringWidget(
            label='Dni',
            label_msgid='quercus1_label_dni',
            description_msgid='quercus1_help_dni',
            i18n_domain='quercus1',
        )
    ),

.............................
But, always it has a Null value in the BD 
Too, I tried to set the property "callStorageOnSet = True" and the problem
continues.
 



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