How to use predicate on object's array of objects values in iOS

Question

I have an Exit object. Every Exit has an array of Category objects.

Objects look like this :

Category: (id, name)

Exit: (id,name,number,...,NSArray(Categories),...)

I want to use NSPredicate to filter out exits by Category name they have in Category array, but I'm not sure how exactly to write it down. If I'd wanted to filter out Exits by Exit name, for example, I would do this

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF.exitName = %@", name];
NSArray *results = [exits filteredArrayUsingPredicate:predicate];

But I'm not sure how to get into the Categories array and search by Category Name.

Any suggestions ?

Try this, NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY SELF.categories.name CONTAINS[c] %@", name]; — Vijay
– Vijay, Commented Nov 3, 2015 at 10:03
categories is an NSArray and does not have a name property. — Avi
– Avi, Commented Nov 3, 2015 at 10:08

Jay Gajjar · Accepted Answer · 2015-11-03 10:00:40Z

1

Try this

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY SELF.exitName.category_name CONTAINS[c] %@", name];
NSArray *results = [exits filteredArrayUsingPredicate:predicate];

answered Nov 3, 2015 at 10:00

Jay Gajjar

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2 Comments

Willeke Over a year ago

SELF is an exit, category_name isn't a property of the name of exit.

Willeke Over a year ago

In the predicateformat, SELF can be seen as an instance of Exit. Exit doesn't have a property exitName, the property is name. This name property doesn't have a property category_name. This predicate won't work.

Avi · Accepted Answer · 2015-11-03 10:17:41Z

0

Try this predicate

NSPredicate *matchingCategory = [NSPredicate predicateWithFormat:@"SUBQUERY(categories, $c, name CONTAINS[cd] %@).@count > 0", categoryName];

Explanation

The SUBQUERY() function creates an array of objects which match the given sub-predicate. In this case, that sub-predicate is name CONTAINS[cd] %@. The way it works is by iterating over the collection (first param), assigning the name $c (second param) to refer to each element and then testing to see if the sub-predicate matches that element. If it matches, it's added to the array.

After the SUBQUERY() completes, the array is aggregated using the @count property. If there were any matches (@count > 0), the overall predicate on the exits will match the exit being tested.

edited Nov 3, 2015 at 10:17

answered Nov 3, 2015 at 10:12

Avi

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5 Comments

Willeke Over a year ago

A subquery is too complicated.

Willeke Over a year ago

Also, filtering all categories and then checking the count is inefficient.

Avi Over a year ago

A solution which works is too complicated, but you don't have any alternative? What's the point of your comment, exactly? And the predicate is turned into SQL, which runs quite efficiently. Why do you think otherwise?

Willeke Over a year ago

See my answer for an alternative. SQL isn't mentioned in the question.

Avi Over a year ago

I thought I read core data somewhere in the question. I apologize for that. Your answer has the unfortunate problem of not actually working.

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