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CoreData fetch query to calculate relationship and group by another relation (m2n)

in my CoreData model I have a n2n relation modeled using an intermediate object:

Person [1<--] Person2Appointment [-->1] Appointment

The object is Person2Appointmentas follows:

@interface Person2Appointment : NSManagedObject

// attributes
@property (nonatomic, retain) NSNumber * participationState;

// relations
@property (nonatomic, retain) Person * person;
@property (nonatomic, retain) Appointment * appointment;
...
@end

(both relations are also modeled as inverse relations for objects Personand Appointment)

I would like to receive an account of all past appointments for all persons.

In SQL, it will look like this:

select count(fk_appointment), fk_person 
  from person2appointment t0
  left join appointment t1 on t0.fk_appointment = t1.pk
where t1.date < ...
group by fk_person;

I tried to use the count-function expression with my select query as follows:

 // create a fetch request for the Person2Appointment entity (category method)
NSFetchRequest* fetch = [Person2Appointment fetchRequest];
fetch.resultType = NSDictionaryResultType;

// count appointments
NSExpression* countTarget = [NSExpression expressionForKeyPath: @"appointment"];
NSExpression* countExp = [NSExpression expressionForFunction:@"count:" arguments: @[countTarget]];
NSExpressionDescription* countDesc = [[NSExpressionDescription alloc]init];
countDesc.name=@"count";
countDesc.expression = countExp;
countDesc.expressionResultType =  NSDecimalAttributeType;

fetch.propertiesToFetch = @["person", countDesc];
fetch.propertiesToGroupBy = ["person"];

fetch.predicate = ...;

After enabling SQL logging, it seems that core-data is executing the correct statement:

SELECT t0.ZPERSON, COUNT( t0.ZAPPOINTMENT) 
  FROM ZPERSON2APPOINTMENT t0 
  JOIN ZAPPOINTMENT t1 ON t0.ZAPPOINTMENT = t1.Z_PK 
  WHERE  t1.ZSTARTDATE > ? GROUP BY  t0.ZPERSON

But the dictionaries in the result array do not contain a numeric number, but instead the target is:

Printing description of d:
{
    count = "0xd0000000000c0018 <x-coredata://BABCBD2E-05AB-4AA5-AC2B-2777916E4EDF/Appointment/p3>";
    person = "0xd0000000000c0016 <x-coredata://BABCBD2E-05AB-4AA5-AC2B-2777916E4EDF/Person/p3>";
}

Is this a mistake in the master data?

Am I doing something wrong here?

?

+4
2

CoreData, , , , count, Person2Appointment Appointment ( , , ?):

NSExpression* countTarget = [NSExpression expressionForKeyPath: @"participationState"];
NSExpression* countExp = [NSExpression expressionForFunction:@"count:" arguments: @[countTarget]];

, , :

NSExpression *countTarget = [NSExpression expressionForEvaluatedObject];
+2

Im , - ,

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(durationMinutes, $a, $a.date < %@)", someDate);
NSInteger count = [managedObjectContext countForEntityForName:@"Person2Appointment" predicate:predicate error:&error];
0

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