Save, Signals and Models

Here is the deal:

class MyModel ( models.Model ):

  title = models.CharField( max_length = 100 )

  only_me = models.BooleanField( default = False )

 Question: Whats the proper way to guarantee that no matter how many MyModel's are available in the database, only one of them

will have the only_me set as True? To further clarify things: In the admin, whenever I check the only_me checkbox, and save my model, all other models of this class will have to have its own only_me field set to false.

 As far as I know, there is no other way of doing this unless I iterate over all MyModel' s objects and uncheck them if they are checked, save them, then afterwards check the model that I am actually saving setting the only_me field to True.

 I tried doing this on the actual save() of the model, no success. Everytime I called save on iterated objects, I, of course, got the maximum recursive depth error thrown at me. 

 Fair enough, I quickly thought about signals, hooking my function to post_save(), however I inevitabilly stumbled upon the same

problem: When I called save() on the iterated objects the post_save signal got sent, I would step again in the same function, thus

no cookie for me.

 I jumped over to overriding AdminForm' s save() method, so that I would iterate there on the models unchecking them if necessary, and them returning the proper object, but I stopped that and I said to myself that I must be doing something really stupid, so Im coming to you guys: What would the propper way of doing this?

Thanks in Advance,

Victor Lima