NSPredicate to check if attribute of object exits, if it does, get it

cocoa-touch, foundation, nsdictionary, nspredicate, objective-c

Solution

The trick here is that in an `NSDictionary`, a non-present key just returns `nil`:

NSArray *dictionaries = @[
    @{ @"Title": @"T1",  @"Cat":   @"Lab",   @"Sex":   @"Male"   },
    @{ @"Title": @"T2",  @"Cat":   @"C2"                         },
    @{ @"Title": @"T3",  @"Cat":   @"Lab",   @"Sex":   @"Female" },
    @{ @"Title": @"T4",  @"Cat":   @"Lab"                        }
];                    

NSPredicate *pred = [NSPredicate predicateWithFormat:@"(Sex == nil OR Sex = 'Male') AND Cat = 'Lab'" ];

NSArray *result = [dictionaries filteredArrayUsingPredicate:pred];

Problem

I'm not even sure of this is possible, but if it is, it could surely help. I have an `NSArray` of `NSDictionarie`s. Each dictionary has certain keys (obviously). ``` Dict{ Title: WBCCount Cat: Lab } Dict{ Title: HbM Cat: Lab Sex: Male } Dict{ Title: HbF Cat: Lab Sex: Female } Dict{ Title: PC_Count Cat: CBC Sex: Female } ``` I wanted to filter array with dictionaries that have `Cat = 'Lab'` and IF `Sex` as a key is present in the dictionary object, get the one with `Male`. In short, I cannot put together a ``` predicateWithFormate:%@" Cat = Lab AND ( if Sex key is present, Sex = Male"; ``` This would get me an array of `WBC, HbM`. I don't know if this is possible, a condition within a predicate, but it would be a life saver if it was as this is how the objects are sent via web API. Any other way of achiving the goal if not this would also be great. While we are in the subject of Core Data, this should be simple: I want to have an attribute of the entity to be able to store either `NSDate` or `NSNumber` or `NSString`. Is there an easy way out?

Original source