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.
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
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...
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.
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
I have a class. Lets call that class MyObject. MyObject has a property called item that is a NSMetadataItem.
NSMetadataItems have an attribute called NSMetadataItemFSNameKey that can be fetched by using this:
NSString *fileName = [myMetadataItem valueForAttribute: NSMetadataItemFSNameKey];
Now I have an array or MyObjects and I want to find what object has an item which NSMetadataItemFSNameKey is the one I am looking for.
OK, I can iterate thru the array using this code:
for (MyObject *oneObj in array) {
NSString *oneFileName = [oneObj.item valueForAttribute:NSMetadataItemFSNameKey];
if ([oneFileName isEqualToString:fileNameItem]) {
// found, do something
}
}
but I am trying to find if it is possible to do that using NSPredicates and filtering?
Is that possible?
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"item.%K = %#", NSMetadataItemFSNameKey, fileNameItem];
NSArray *filteresArray = [array filteredArrayUsingPredicate:predicate];
Typed in Safari.
Suppose I have the following objects
class A {
NSArray *arrayOfB;
}
class B {
NSString *name;
}
Now, I have an array of As like below and each A contains 10 objects of B within its property arrayOfB.
NSArray *arrayOfAs; //contains objects of A
How can I get the objects of A depending upon specific match of name property of Bs inside of A, by using NSPredicate ?
I've tried googling, etc. and even writing various style of NSPredicate but did not succeed. Can anyone enlighten me how to do it?
This is what I tried so far:
NSPredicate *p = [NSPredicate predicateWithFormat:#"(SELF.name BEGINSWITH[c] %# IN SELF.arrayOfB)",myText];
NSArray *mySearchedArrayOfAs = [arrayOfAs filteredArrayUsingPredicate:p];
But I run into error which says "Unable to parse the predicate".
I think you need to use ANY operator, like this:
NSPredicate *p = [NSPredicate predicateWithFormat:#"ANY arrayOfB.name BEGINSWITH[c] %#", myText];
I have an NSMangedObject that contains NSSet of other NSManagedObjects.
I need to check if these objects has an value in NSSet and then return them.
I use MagicalRecord for fetching data.
So I need something like this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"stringObjects contains %#", string];
So if NSSet stringObjects contains some string that I am looking for so then return object I have requested.
One note here: stringObjects (name just for example it represent my NSSet) it is NSSet that contains NSManagedObjects, so I need to search them by some id (for example string_id attribute).
So then model looks like this
NSSet *set = MainObject.stringObjects;
NSString *string_id_for_first_object = [[[set allObjects] objectAtIndex:0] string_id];
Just for better understanding relationship.
But the question is about how can I create predicate to check if NSSet contains needed id.
If I understand your question correctly, stringObjects is a to-many relationship
from one entity A to another entity B, and B has an attribute string_id.
To find all A objects that are related to any B object with the given string id, use:
NSString *stringId = …; // The string that you are looking for
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ANY stringObjects.string_id == %#", stringId];
EntityA has a to-many relationship to EntityB (and EntityB has a to-one relationship to EntityA). I have an array of EntityBs (or more accurately, I have an NSArray that contains instances of NSManagedObject which represent EntityB). I want to create an NSFetchRequest that will fetch all EntityAs that have a relationship to at least one of the EntityBs in the array. How do I write the predicate for this fetch request?
The following works, but I think it is sub-optimal; it's hard to grok and I'm sure there must be a better way of expressing this:
NSArray *entityBs = ...;
NSMutableArray *containsEntityBSubPredicates = [NSMutableArray new];
for (NSManagedObject *entityB in entityBs) {
[containsEntityBSubPredicates addObject:[NSPredicate predicateWithFormat:#"%# IN entityBs", entityB]];
}
NSPredicate *containsEntityBsPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:containsEntityBSubPredicates];
I've also tried this, but it doesn't work:
NSArray *entityBs = ...;
NSPredicate *containsEntityBsPredicate = [NSPredicate predicateWithFormat:#"ANY %# in entityBs", entityBs];
Am I missing a simpler solution?
You were almost there with your predicate, just switch the parameters:
[NSPredicate predicateWithFormat:#"ANY entityBs in %#", entityBArray];
Look at Apple's example code with IN here for further explanation.