iOS : Core Data - Get Core Data Objects by Function

GetCoreDataByFunction.m

NSManagedObjectContext *context = <#Get the context#>;
 
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"<#Entity name#>" inManagedObjectContext:context];
[request setEntity:entity];
 
// Specify that the request should return dictionaries.
[request setResultType:NSDictionaryResultType];
 
// Create an expression for the key path.
NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:@"<#Key-path for the property#>"];
 
// Create an expression to represent the function you want to apply
NSExpression *expression = [NSExpression expressionForFunction:@"<#Function name#>"
    arguments:@[keyPathExpression]];
 
// Create an expression description using the minExpression and returning a date.
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
 
// The name is the key that will be used in the dictionary for the return value.
[expressionDescription setName:@"<#Dictionary key#>"];
[expressionDescription setExpression:expression];
[expressionDescription setExpressionResultType:<#Result type#>]; // For example, NSDateAttributeType
 
// Set the request's properties to fetch just the property represented by the expressions.
[request setPropertiesToFetch:@[expressionDescription]];
 
// Execute the fetch.
NSError *error;
id requestedValue = nil;
NSArray *objects = [context executeFetchRequest:request error:&error];
if (objects == nil) {
    // Handle the error.
}
else {
    if ([objects count] > 0) {
        requestedValue = [[objects objectAtIndex:0] valueForKey:@"<#Dictionary key#>"];
    }
}