Ah, alright, thanks for the reply!
So firstly: at the beginning it actually worked to insert something in the treeview with model.setquery("SELECT * FROM VOCABULARY"). It inserted exactly what i wanted. But then it wasn't possible to do anything else. But through that (and from tkinter treeview) I know, that it only turns hirarchical if you want it to e.g. set parent items and give them child items.

Secondly, my controller does this to start the model:

Qt Code: 
  1. def start_mode(self):
  2.         self.start_vocab = model("data/start.db", "load")
  3.         self.main_win.vocab_tv.setModel(self.start_vocab)
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(vocab_tv is the treeview)

And thirdly, I also checked the location of the file - tested it with the sqlite3 module simultaneously, if it works. Sqlite3 returns everything as plannend!

This is the craziest thing!

So here the logic broken down:

1.) Create and instantiate a model, inherited from QSqlTableModel.
2.) Add the Database QSQLITE (In this case)
3.) Set the DatabaseName: the database File
4.) Optional: Set EditStrategy
5.) Set the Table - which is the one it reads from the file
6.) Make it select()
7.) Create a Treeview or Listview
8.) Set the model for the Treeview or Listview

That should be it, right!?