Error 1022 - Can't write; duplicate key in table

The most likely you already have a constraint with the name iduser or idcategory in your database. Just rename the constraints if so.

Constraints must be unique for the entire database, not just for the specific table you are creating/altering.

To find out where the constraints are currently in use you can use the following query:

SELECT `TABLE_SCHEMA`, `TABLE_NAME`
FROM `information_schema`.`KEY_COLUMN_USAGE`
WHERE `CONSTRAINT_NAME` IN ('iduser', 'idcategory');

Change the Foreign key name in MySQL. You can not have the same foreign key names in the database tables.

Check all your tables and all your foreign keys and avoid having two foreign keys with the same exact name.

From the two linksResolved Successfully and Naming Convention, I easily solved this same problem which I faced. i.e., for the foreign key name, give as fk_colName_TableName. This naming convention is non-ambiguous and also makes every ForeignKey in your DB Model unique and you will never get this error.

Error 1022: Can't write; duplicate key in table