Plone: Query Archetype content items/objects inside a particular folder during content submission
Alternative 1: Use PloneFormGen, make a form with a button and an action adapter. The button is called "Apply". The action adapter has a python script that checks if user has already applied, if so redirects to edit view of existing item, if not calls invokeFactory on the Applications folder. You may want to hide the "Add content" menu, possibly simply with CSS for that location.
Alternative 2: Make an event handler that intercepts creating content on the folder. Might also work with a content rule. Try a content rule and see when it kicks in, otherwise you can make an event handler that can intercept at the right time. One can start with listening for zope.event (I believe it's called or somesuch) which is the base class for all events and log the events generated when you add content. Pick an event the seems right and add python code that redirects to edit view of existing item or just lets the content creation process go on if the user has not already applied.
Is it possible to access or navigate saved content items under the same folder during every content submission so that every content submitted must be verified to avoid submission of content that already exists? I have application content type where members can submit their applications but shouldn't accept applications more than one per member. If yes, please help me. Thanks in advance.