How Restrict the User to only one Request per catalog item?

[Gowtham Kodali]

 how can we restrict the user to only one request per catalog item if he has already  an existing open request  for that catalog item.

for example 

If a user has an open request on  catalog item  'X' again he is trying to raise the request  for the same catalog item i want to restrict him from raising the request in such case how is it possible

[hallief]

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To stop a user from making more than one request for the same thing, like, say, item 'X' in a catalog, you gotta check if they already got a request for that item. If they do, just tell 'em, "Hey, you already got one request for this, buddy!" and don't let 'em make another one. Simple as that