I am assuming on click of + button for creating a WO, the application is calling pyStartCase flow. Did you check "Start Setting" under Process tab in the flow. We have the option to "Create a new Work Object", I think disabling this option should help in your case.
Hello, You say you're requirements are the following
User presses "+" button.
System creates a temporary page defined on ....-Work-... class
Then system opens the assignment
If user press save or submit button this temp page should be recorded to database as new WO. Else this page must be deleted.
What assignment are you opening if you don't have a work object persisted to the database yet? Are you running a flow on an object with pyTemporaryObject set to true? That won't create assignments in the database (since an assignment assumes persistence). I suspect I may be missing some aspect of what you are trying to do. If my understanding is correct, I don't think what you want to do will work. It might help to take a step back and discuss the business problem that you are trying to solve. Ultimately, I believe you want a user to press the "+" button, have a new tab open, for data to be input in that new tab, and based on that input to either enter a new work object or not. Is that correct?