Keypath for first element in embedded NSArray
This example is contrived, but it shows my point.
So, if I have an object graph like the following:
{
sex = male;
uid = 637650940;
work = ({
employer = {
id = 116420715044499;
name = "Software Engineer";
};
"end_date" = "0000-00";
"start_date" = "0000-00";
}, {
employer = {
id = 188733137832278;
name = "Apple";
};
});
},
//Some more objects
(This is an NSArray containing NSDictionarys that have an object of type NSArray).
The key field is work . I want a Key Path that will take the first object in the work array.
If I do this:
NSArray* work = [outerArrayObject objectForKey: @"work"];
id name = [work valueForKeyPath: @"employer.name"];
I get an array containing each name (In the above case, Software Engineer & Apple). Is there a collection operator or something to return the first object? Bonus points if you can develop a Key Path to sort each work by start_date also :)
Well to answer my own question, one way to do it is this:
1) Define the following category
@implementation NSArray (CustomKVOOperators)
- (id) _firstForKeyPath: (NSString*) keyPath {
NSArray* array = [self valueForKeyPath: keyPath];
if( [array respondsToSelector: @selector(objectAtIndex:)] &&
[array respondsToSelector: @selector(count)]) {
if( [array count] )
return [array objectAtIndex: 0];
else
return nil;
}
else {
return nil;
}
}
@end
2) Use this KeyPath syntax
NSArray* work = [outerArrayObject objectForKey: @"work"];
id name = [work valueForKeyPath: @"@first.employer.name"];
Thanks to this clever person.
@PauldeLange - Your answer and links were helpful.
The following simpler version works too (at least as of Xcode 6)
id name = [work valueForKeyPath: @"employer.name.@firstObject”];
In the above 'firstObject' refers to the predefined method on NSArray. If the second object is needed, you can define the following:
@implementation NSArray (CustomKVOOperators)
- (id) secondObject {
return [self count] >=2 ? self[1] : nil;
}
@end
And use:
id name = [work valueForKeyPath: @"employer.name.@secondObject”];
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