How to fetch data from already saved nodes to the edit-form for node creation? I have this scenario: a content-type A (event) has an entity-reference to another content-type B (location). Now, if an editor adds a new event and enters the (already existing) location by "autocomplete" or dropdown-list, i want to display all other events referenced to that location in the edit form to prevent dups (and redundant work).

I imagine this like a "check colliding events for this location"-button, that is triggering a view perhaps, but it has to be "before" saving the new node.

I already tried a bit with Rules-module, but there's probably no way to trigger this, though the rules-event "before saving new content" is just one step to late, because all the work is already done and all fields are filled... 

Is there an approach on module-level for this or do i have to dive into modifying hook_form_alter?

Can someone point me in the right direction?
Thanks a lot in advance.

(Drupal 7.14, Views 7.x-3.3+122-dev, Calendar 7.x-3.3+0-dev, Date 7.x-2.5+8-dev, BEF, Address Field 7.x-1.0-beta2)



Update: So far i achieved an approach with a combination of Views and Panels. I override the standard "Node add/edit form" with a panel for my content-type A. To show the nodes of Content-Type B i added a view to that panel. They are shown in a two-column layout. 

This works until i bring the "check" into the game. I added an exposed filter to the view, but when i use it, the node form is submitted instead of showing the filtered view. 

I opened another question on this issue: Exposed filter of a view embedded in a panel overriding a node form triggers node submission. How to prevent this?

Question: Am I totally wrong with this approach (Panel with View and Form)? 

Is it possible to have a custom form with the exposed filter "before" the node form to use the results of the filter to show the view?

I'm lost a bit...

Any help highly appreciated...
SOLVED: 

Via http://drupal.org/node/1028952#comment-3968840 i found this little module 

http://github.com/Itangalo/Node-creation-block--Drupal-7-

that resolved my issue.

Another possibilty (although in dev-status) is the use of this module: http://drupal.org/project/formblock