NSExpression using sqrt: function results in NSInvalidArgumentException

Question

I'm getting an NSInvalidArgumentException:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unsupported function type passed to SQL store'

When trying to use an NSExpression to take the square root of a nested NSExpression which is using the "multiply:by:" function.

My code looks like this:

NSManagedObjectContext *context=[[BDCoreDataController sharedController] mainManagedObjectContext];
NSFetchRequest *theRequest=[[NSFetchRequest alloc] init];

[theRequest setEntity:[NSEntityDescription entityForName:@"BDCompanyEntity" inManagedObjectContext:context]];
theRequest.resultType=NSDictionaryResultType;

NSExpression *constantExpression=[NSExpression expressionForConstantValue:[NSNumber numberWithDouble:22.5]];
NSExpression *firstKeyPath=[NSExpression expressionForKeyPath:@"epsTTM"];
NSExpression *secondKeyPath=[NSExpression expressionForKeyPath:@"bookValuePerShare"];

NSExpression *firstMultiplyExpression=[NSExpression expressionForFunction:@"multiply:by:" arguments:@[firstKeyPath,secondKeyPath]];

NSExpression *secondMultiplyExpression=[NSExpression expressionForFunction:@"multiply:by:" arguments:@[firstMultiplyExpression,constantExpression]];

NSExpression *sqrtExpression=[NSExpression expressionForFunction:@"sqrt:" arguments:@[secondMultiplyExpression]];

NSExpressionDescription *expressionDescription=[[NSExpressionDescription alloc] init];
[expressionDescription setName:@"grahamNumber"];
[expressionDescription setExpression:sqrtExpression];
[expressionDescription setExpressionResultType:NSDoubleAttributeType];

[theRequest setPropertiesToFetch:@[expressionDescription,@"name"]];

NSError *fetchError;
NSArray *grahams=[context executeFetchRequest:theRequest error:&fetchError];

Executing the fetch with just trying to evaluate the nested "multiply:by:" works fine with this code:

NSManagedObjectContext *context=[[BDCoreDataController sharedController] mainManagedObjectContext];
NSFetchRequest *theRequest=[[NSFetchRequest alloc] init];

[theRequest setEntity:[NSEntityDescription entityForName:@"BDCompanyEntity" inManagedObjectContext:context]];
theRequest.resultType=NSDictionaryResultType;

NSExpression *constantExpression=[NSExpression expressionForConstantValue:[NSNumber numberWithDouble:22.5]];
NSExpression *firstKeyPath=[NSExpression expressionForKeyPath:@"epsTTM"];
NSExpression *secondKeyPath=[NSExpression expressionForKeyPath:@"bookValuePerShare"];

NSExpression *firstMultiplyExpression=[NSExpression expressionForFunction:@"multiply:by:" arguments:@[firstKeyPath,secondKeyPath]];

NSExpression *secondMultiplyExpression=[NSExpression expressionForFunction:@"multiply:by:" arguments:@[firstMultiplyExpression,constantExpression]];

NSExpressionDescription *expressionDescription=[[NSExpressionDescription alloc] init];
[expressionDescription setName:@"grahamNumber"];
[expressionDescription setExpression: secondMultiplyExpression];
[expressionDescription setExpressionResultType:NSDoubleAttributeType];

[theRequest setPropertiesToFetch:@[expressionDescription,@"name"]];

NSError *fetchError;
NSArray *grahams=[context executeFetchRequest:theRequest error:&fetchError];

At first I thought that perhaps the "sqrt" NSExpression was having trouble with the nested NSExpression. So I tried just a constant NSExpression. The following code tries to just take evaluate a constant in the sqrt NSExpression. It causes the same NSInvalidArguementException

NSManagedObjectContext *context=[[BDCoreDataController sharedController] mainManagedObjectContext];
NSFetchRequest *theRequest=[[NSFetchRequest alloc] init];

[theRequest setEntity:[NSEntityDescription entityForName:@"BDCompanyEntity" inManagedObjectContext:context]];
theRequest.resultType=NSDictionaryResultType;

NSExpression *constantExpression=[NSExpression expressionForConstantValue:[NSNumber numberWithDouble:22.5]];

NSExpression *sqrtExpression=[NSExpression expressionForFunction:@"sqrt:" arguments:@[constantExpression]];

NSExpressionDescription *expressionDescription=[[NSExpressionDescription alloc] init];
[expressionDescription setName:@"grahamNumber"];
[expressionDescription setExpression:sqrtExpression];
[expressionDescription setExpressionResultType:NSDoubleAttributeType];

[theRequest setPropertiesToFetch:@[expressionDescription,@"name"]];

NSError *fetchError;
NSArray *grahams=[context executeFetchRequest:theRequest error:&fetchError];

any ideas what could be causing the problem?

Thanks

toolman

score 3 · Accepted Answer · answered May 14 '15 at 17:34

Not every expression that's valid for NSExpression is valid for use when fetching from Core Data when using a SQLite store. Unfortunately sqrt: is not supported for this kind of use. It would probably work with a binary store, but that loses many of the advantages of Core Data (it would mean loading all data into memory at once, for example).

What's especially annoying is that there's no documented list that indicates which functions are supported for use with Core Data. But the error message is exactly correct: Although this function is valid for use with NSExpression, it's not valid for use with a SQLite persistent store.

Not the answer I'd like to give, because I could really use `sqrt` there too, but that's life sometimes. — Tom Harrington, May 14 '15 at 23:25

score 0 · Answer 2 · answered May 14 '15 at 06:32

0

sqrt: function seems to be available on OS X since v10.5, but not on iOS.

See the documentation: https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSExpression_Class/index.html#//apple_ref/occ/clm/NSExpression/expressionForFunction:arguments:

answered May 14 '15 at 06:32

Nicolas Buquet

3,880
28
28

thanks for the answer! Looking at the IOS 8.3 headers, though, it shows that sqrt: is a supported function. for `+ (NSExpression *)expressionForFunction:(NSString *)name arguments:(NSArray *)parameters;` – timthetoolman May 14 '15 at 15:49
1

It was even listed in iOS 4.0: http://developer.limneos.net/index.php?ios=4.0&framework=Foundation.framework&header=NSExpression.h, but I think it is the same header as OS X, but implementation differ. – Nicolas Buquet May 14 '15 at 16:43

NSExpression using sqrt: function results in NSInvalidArgumentException

2 Answers2