Parse.com: How to properly check if a field is empty? - ios

Question

I ask this in the context of a iOS / Swift app:
When retrieving with a query an object from Parse, I used to check for empty fields by checking them against nil. if != nil.... then do this etc etc....
Apparently, this is not the proper way to do this, because even if a field is empty on Parse, it is NOT considered nil by swift.
So what to to check for to determine if a field is empty or not, and for the various Parse supported types: strings, Number, Array.....?
Edit: there are answers for objective-c that don't work in swift where unless value is a boolean you MUST compare it against nil (which cause issue here) or something else to see if it exists or not.

Answer 1

You would use whereKeyExists:
Checkout the Parse documentation
If you want to retrieve objects that have a particular key set, you can use whereKeyExists. Conversely, if you want to retrieve objects without a particular
key set, you can use whereKeyDoesNotExist.
// Finds objects that have the score set
[query whereKeyExists:#"score"];

Answer 2

Ok so here is what I found after some investigation:
A String field when it looks empty on parse explorer, in fact contains "". It is only when the field specifically has "undefined" in it that it is nil, which you can compare against with === and not ==. Not sure why, if someone knows....
Other fields than String, cannot contain "". They either contain a value or are undefined.
So if you need to know if a field is nil or contains no value, if it's a string compare it against == "" and === nil, and use === nil if it's not a string.

Answer 3

This is what I used to check whether a field containing a file is null. Since the value can be (undefined) or (null).
func isParseNull(obj : AnyObject!) -> Bool {
if obj == nil {
return true
}
if obj as NSObject == NSNull() {
return true
}
return false
}

Answer 4

I'm pretty sure the Parse documentation says !=nil however you could try
entity == ""

Answer 5

I would extend String class and do the following
extension String {
func isOnlyEmptySpacesAndNewLineCharacters() -> Bool {
return self.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet()).length == 0
}
}

Answer 6

Here is my method, as I also struggled to check to see whether a string was empty in parse, and this seems to work fine.
- (void) nameCheck
{
//--------GET CURRENT USER-------//
PFUser *user = [PFUser currentUser];
//----------CHECK IF PARSE IS EMPTY OR TEXTFIELD IS EMPTY-----------//
if ([user[#"fullname"] isEqual: #""] || [fieldName.text isEqual:nil])
{
//-IF EMPTY, GIVE USER ANONYMOUS NAME-//
user[#"fullname"] = #"Anonymous User";
user[#"fullname_lower"] = #"anonymous user";
//------------------SAVE NEW NAME IN BACKGROUND----------------//
[user saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error)
{
if (error == nil)
{
NSLog(#"Saved Username");
}
}];
}
//--ELSE USER'S NAME EXISTS--//
else
{
//--LOAD USER METHOD--//
[self loadUser];
NSLog(#"User has username");
}
}