Check if an object exists

Question

I need to check if Model objects filter      turned up anything  but do not need to insert anything  My code so far is   user pass   log in request POST     form class if user pass is valid        cleaned info   user pass cleaned data     user object   User objects filter email   cleaned info  username

User · Answer

You can use   try       get your models except ObjectDoesNotExist       do something

User · Answer

If the user exists you can get the user in user object else user object will be None   try      user object   User objects get email   cleaned info  username    except User DoesNotExist      user object   None if user object        user exist     pass else        user does not exist     pass

User · Answer

You can also use get object or 404    it will raise a Http404 if the object wasn t found   user pass   log in request POST   form class if user pass is valid        cleaned info   user pass cleaned data     user object   get object or 404 User  email cleaned info  username          User object found  you are good to go

User · Answer

I think the easiest from a logical and efficiency point of view is using the queryset s exists   function  documented here   https   docs djangoproject com en stable ref models querysets  django db models query QuerySet exists  So in your example above I would simply write   if User objects filter email   cleaned info  username    exists          at least one object satisfying query exists else        no object satisfying query exists

User · Answer

the boolean value of an empty QuerySet is also False  so you could also just do         if not user object     do insert or whatever etc

User · Answer

Since filter returns a QuerySet  you can use count to check how many results were returned   This is assuming you don t actually need the results   num results   User objects filter email   cleaned info  username    count     After looking at the documentation though  it s better to just call len on your filter if you are planning on using the results later  as you ll only be making one sql query      A count   call performs a SELECT COUNT    behind the scenes  so you should always use count   rather than loading all of the record into Python objects and calling len   on the result  unless you need to load the objects into memory anyway  in which case len   will be faster     num results   len user object

[python] Check if an object exists

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