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POHow do you construct the predicate for NSFetchRequest setHavingPredicate:?
 

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  1. POHow do you construct the predicate for NSFetchRequest setHavingPredicate:?
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    <p>For the life of me I can not seem to get this to work.</p> <p>Assume our entity is an managed object with a status field and an order field.</p> <p>How would I go about getting all orderedEntries having more than one order that are the same?</p> <p><strong>Please no answers telling me to just do a subquery with @count in the main predicate, since I know of that solution, the point of this post is to understand how to use the having predicate in core data, which would probably be faster than a subquery anyways. (unless you explain why I can not use a having clause)</strong></p> <p>The following code would return an array of dictionaries with the number of orders per order number. What I want is to be able to add a having clause to restrict my request to only return the dictionaries representing objects of those orders that have a count greater than 1.</p> <p>Here is the code so far and my attempts at a having predicate:</p> <pre><code>NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"OrderedEntry" inManagedObjectContext:context]; [fetchRequest setEntity:entity]; [fetchRequest setResultType:NSDictionaryResultType]; NSPredicate *predicate = [NSPredicate predicateWithFormat: @"(status == %@)",[NSNumber numberWithInt:EntryStatusAlive]]; [fetchRequest setPredicate:predicate]; NSExpression *keyPathExpression = [NSExpression expressionForKeyPath: @"order"]; // Does not really matter NSExpression *maxExpression = [NSExpression expressionForFunction: @"count:" arguments: [NSArray arrayWithObject:keyPathExpression]]; NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init]; [expressionDescription setName: @"orderCount"]; [expressionDescription setExpression: maxExpression]; [expressionDescription setExpressionResultType: NSInteger32AttributeType]; [fetchRequest setPropertiesToFetch: [NSArray arrayWithObjects:expressionDescription,@"order",nil]]; [fetchRequest setPropertiesToGroupBy:[NSArray arrayWithObjects:@"order",nil]]; //[fetchRequest setHavingPredicate:[NSPredicate predicateWithFormat:@"@count &gt; 1"]]; //[fetchRequest setHavingPredicate:[NSComparisonPredicate predicateWithLeftExpression:maxExpression rightExpression:[NSExpression expressionForConstantValue:[NSNumber numberWithInteger:1]] modifier:NSDirectPredicateModifier type:NSGreaterThanPredicateOperatorType options:NSCaseInsensitivePredicateOption]]; NSError *error; NSArray * array = [context executeFetchRequest:fetchRequest error:&amp;error]; </code></pre>
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    1. CODid you ever get an answer on this? I have found many useless references to 'setHavingPredicate' that provide no indication of what the format of this predicate needs to be. No working examples, and nothing that I have tried has worked...
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    2. CO@ChristopherKing Nope not at all, I basically gave up, there is NO information on the web and the apple web forums are not more helpful. I really believe no one uses this, as it's very easy to construct the same functionality of the Having predicate just by doing a normal fetch and then shifting through the data with a filter or manually with a loop. We want to know because there's always the 'right way' to do something, especially if the api is provided.
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