CODEWITHSUNDEEP
objective-ccore-data
A.C. Wright
A.C. Wright

Reputation: 941

'Unsupported function expression CAST...' when using NSPredicate with SQLite Core Data store type

I'm attempting a fetch request with the following code:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"dateModified > CAST(CAST(now(), \"NSNumber\") - %d, \"NSDate\")", (30*86400)];
NSFetchRequest *itemRequest = [NSFetchRequest fetchRequestWithEntityName:@"Item"];
[itemRequest setPredicate:predicate];

NSArray *items = [[self managedObjectContext] executeFetchRequest:itemRequest error:nil];

...in order to fetch items where the 'dateModified > |now() - 30 days|'. The problem is that the above predicate works correctly (fetches properly) until I save my NSPersistentDocument as SQLite and re-open the document. When I re-open the document I get the following error:

Unsupported function expression CAST(CAST(now(), "NSNumber") - 2592000, "NSDate")

Why does this predicate work correctly up until save or if I save the document as XML, but does not work correctly if I save as SQLite? Is there a way to use this predicate with the SQlite store type?

P.S. I have also tried forming the predicate with the following code but get the same error:

//"now()" is a function and takes no arguments
NSExpression * now = [NSExpression expressionForFunction:@"now" arguments:[NSArray array]];

//CAST(now(), 'NSNumber')
NSArray * castNowArguments = [NSArray arrayWithObjects:now, [NSExpression expressionForConstantValue:@"NSNumber"], nil];
NSExpression * castNow = [NSExpression expressionForFunction:@"castObject:toType:" arguments:castNowArguments];

//CAST(now(), 'NSNumber') [+/-] {a time interval}
NSArray * relativeTimestampArguments = [NSArray arrayWithObjects:castNow, [NSExpression expressionForConstantValue:[NSNumber numberWithDouble:(30*86400)]], nil];
NSExpression * relativeTimestamp = [NSExpression expressionForFunction:@"from:subtract:" arguments:relativeTimestampArguments];

//CAST(CAST(now(), 'NSNumber') [+/-] {a time interval}, 'NSDate')
NSArray * castToDateArguments = [NSArray arrayWithObjects:relativeTimestamp, [NSExpression expressionForConstantValue:@"NSDate"], nil];
NSExpression * castToDate = [NSExpression expressionForFunction:@"castObject:toType:" arguments:castToDateArguments];

NSPredicate *predicate = [NSComparisonPredicate predicateWithLeftExpression:[NSExpression expressionForKeyPath:@"dateModified"] 
                                                            rightExpression:castToDate 
                                                                   modifier:NSDirectPredicateModifier
                                                                       type:NSGreaterThanOrEqualToComparison 
                                                                    options:0];

Upvotes: 2

Views: 1528

Answers (2)

Fedor Pudeyan
Fedor Pudeyan

Reputation: 39

Following code worked out just well in my case:

now() - 2592000

Upvotes: 1

A.C. Wright
A.C. Wright

Reputation: 941

I found my own solution...

Function calls are unsupported when fetching data from a SQLite store type. It is only possible to use function calls in fetches for in-memory data. In order to still use this predicate I had to first fetch the data set and then filter the array using:

[allItems filteredArrayUsingPredicate:predicate];

Hope this helps someone!

Upvotes: 2

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