[Mark Goebl]

Hi,

I've started with Core Data and binding and it's quite easy to use.

I started with filtering my entities and everything works find.

But now I would like to get @sums and group some data. How could I do that:

e.g.:

my Entity has 3 Attributes: name, periode and Amount.

I would like to have a NSTableview which shows name, @sum(Amount).

Do I need to create a custon class or is there another way?

Thanks Mark

[Mark Goebl]

would like to precise my problem:
Thinking in SQL-Statements I would like to get the following SQL query:

SELECT name, SUM(amount) FROM Entity GROUP BY name

and display the result in a NSTableview.

How do I get this result?

Thanks Mark

[bewebste]

I don't believe there's a simple (i.e. codeless) way to do what you're describing. Key-value coding does provide an @sum operator, which lets you do things like:

sumOfAmounts = [myArray valueForKeyPath:@"@sum.amount"];

This will get you the sum of all the amounts, but there's no way for KVC to do the grouping you want.

The way I'd approach it would probably be to make another entity that represents a group of your original entities, let's call it EntityGroup. This entity would have an attribute for "name", and a to-many relationship to your original entity, let's call it "subentities". The creation of these objects would have to be done in code, although searching for entities with a given name could be helped along by using an NSFetchRequest. Your table would then display these EntityGroup objects, with the columns bound to "name" and "subentities.@sum.amount".

Another hint: if you want to get a list of the unique names in a collection of objects, try [myArrayOrSetOfObjects valueForKeyPath:@"@distinctUnionOfObjects.name"]