use NSPredicate to filter object - ios

Question

Here say I have a array of objects with two attributes:
// array of object
NSArray *objects
// object
NSString *primaryTag;
NSArray *secondaryTag;
Since what I want is when the this object contains the givenTag, it could be passed to a new array called results;
Here is my codes:
NSPredicate *resultPredicate = [NSPredicate predicateWithFormat:#"primaryTag == %# || secondaryTag CONTAINS[c] %#", givenTag, givenTag];
results = [objects filteredArrayUsingPredicate:resultPredicate];
It seems that the primaryTag works well, but the secondaryTag doesn't work, can someone help me out. I am not that familiar with NSPredicate filtering. Thanks in advance.

Answer 1

The most efficient way to do that is with a NSCompoundPredicate like so:
NSArray *subPredicates = #[tag1, tag2, tag3];
NSPredicate *compoundPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:subPredicates];
Your question is a little unclear so you might also want:
andPredicateWithSubpredicates
Depending on exactly what the nature of the result set you are looking for.
See Apple Docs here: NSCompoundPredicate Docs

Answer 2

i implemented the following custom class:
#interface CustomObject : NSObject
#property (copy, nonatomic) NSString *primaryTag;
#property (strong, nonatomic) NSArray *secondaryTag;
#end
and overrode it's description method for the NSLog statement to print something we understand:
- (NSString *)description {
return [NSString stringWithFormat:#"primaryTag: %#, secondaryTag: %#", _primaryTag, [_secondaryTag componentsJoinedByString:#", "]];
}
then i created some objects from the custom class and added them to an array:
NSMutableArray *objects = [NSMutableArray array];
CustomObject *obj1 = [CustomObject new];
obj1.primaryTag = #"stringToSearchFor";
obj1.secondaryTag = #[#"notTheStringToSearchFor", #"somethingElse"];
[objects addObject:obj1];
CustomObject *obj2 = [CustomObject new];
obj2.primaryTag = #"differentString";
obj2.secondaryTag = #[#"nothingWeAreLookingFor"];
[objects addObject:obj2];
CustomObject *obj3 = [CustomObject new];
obj3.primaryTag = #"anotherOne";
obj3.secondaryTag = #[#"whoCaresForThisString", #"stringToSearchFor"];
[objects addObject:obj3];
finally i created a string to search for and the predicate:
NSString *givenTag = #"stringToSearchFor";
NSPredicate *resultPredicate = [NSPredicate predicateWithFormat:#"primaryTag == %# || secondaryTag CONTAINS[c] %#", givenTag, givenTag];
when i log out the result i get the correct results:
NSLog(#"%#", [objects filteredArrayUsingPredicate:resultPredicate]);
logs:
(
"primaryTag: stringToSearchFor, secondaryTag: notTheStringToSearchFor, somethingElse",
"primaryTag: anotherOne, secondaryTag: whoCaresForThisString, stringToSearchFor"
)
which is obj1 and obj3. correct! if it does not work for you there's gotta be something else wrong with your code...

Answer 3

If my understanding of the original question is incorrect, please let me know, and I will adjust my answer.
Problem: You have an array of objects with 2 properties. One is primaryTag, which is a string. The second is an array of secondaryTags, which is a collection of strings. You want to filter all objects where either the primaryTag matches, or where the search string matches one of the secondaryTags.
Answer The proper way to match strings is via MATCHES or CONTAINS.
NSPredicate *pPredicate =
[NSPredicate predicateWithFormat:#"%K CONTAINS[cd] %#",
#"primaryTag", searchString];
NSPredicate *sPredicate =
[NSPredicate
predicateWithFormat:#"SUBQUERY(%K, $st, $st CONTAINS[cd] %#).#count > 0",
#"secondaryTags", searchString];
NSCompoundPredicate *searchPredicate =
[NSCompoundPredicate orPredicateWithSubPredicates:#[ pPredicate, sPredicate ]];
How it works: The first predicate is a straightforward match. You can replace CONTAINS with MATCHES, if that better fits the kind of comparison you wish to make. The [cd] suffix means case-insensitive and diacritic-insensitive. It's normal to include those when searching/filtering, but again, it's up to you. Instead of embedding the property name in the predicate format string, I use %K and a replacement parameter. In production code, that replacement parameter would be a constant.
The second predicate is a little trickier. It uses a SUBQUERY() to filter the secondaryTags array, and returns the object as matching if at least one secondary tag matches the search string. SUBQUERY() is a function with 3 parameters. The first is the collection being searched. The second is a temporary variable that represents each item in the collection, in turn; it is used in the 3rd parameter. The 3rd parameter is a regular predicate. Each item in the collection that matches the filter is included in the output of SUBQUERY(). At the end, the matching secondary tags are counted (via #count), and if the count is greater than zero, the original object is considered to have matched, so will be included in the filtered output.
Finally, we combine these two predicates into one searchPredicate, which can now be used to filter your array of objects.

Answer 4

I seen this issue,
My normal approch is to use the NSPredicate twice,
So that I can track the result at every steps:
Option 1:
NSPredicate *resultPredicate1 = [NSPredicate predicateWithFormat:#"primaryTag == %#", givenTag];
results1 = [objects filteredArrayUsingPredicate:resultPredicate1];
NSPredicate *resultPredicate2 = [NSPredicate predicateWithFormat:#"secondaryTag CONTAINS[c] %#", givenTag];
finalResults = [results1 filteredArrayUsingPredicate:resultPredicate2];
Option 2:
Use NSCompoundPredicate to compound multiple filtering. You can easily find many examples on google and stackOverFlow.
Hope this will help,
Thanks