Re: Can CoreData return only unique results of an attribute
Re: Can CoreData return only unique results of an attribute
- Subject: Re: Can CoreData return only unique results of an attribute
- From: Jim Murry <email@hidden>
- Date: Tue, 26 Feb 2008 19:27:36 -0800
It may be, but one would have to take the steps to make sure that each
item is unique. NSMutableDictionary does that automatically.
Jim
On Feb 26, 2008, at 7:18 PM, Andy Lee wrote:
Wouldn't it be cheaper to put the URLs into an NSMutableSet, if
you're discarding the names anyway?
--Andy
On Feb 26, 2008, at 9:08 PM, Jim Murry wrote:
Populate an NSMutableDictionary using our objects:
setObject:@"Sam" forKey:@"http://www.aol.com";
setObject:@"Adam" forKey:@"http://www.digg.com";
setObject:@"Jane" forKey:@"http://www.ibm.com";
setObject:@"John" forKey:@"http://www.aol.com";
then use allKeys from dictionary to return the unique keys:
http://www.digg.com
http://www.ibm.com
http://www.aol.com
On Feb 26, 2008, at 4:34 PM, Adam Gerson wrote:
Thanks for the example. What I am looking for is slightly diferent.
Lets say I have a entity called FavoriteWebsites with the attributes
name and url. The current contents of the object are
Name | URL
---------------------------------------------
Sam | http://www.aol.com
Adam | http://www.digg.com
Jane | http://www.ibm.com
John | http://www.aol.com
I want to filter for only the unique values of url, so the list I
want
to get back for a separate table is
http://www.digg.com
http://www.ibm.com
http://www.aol.com
Perhaps NSPredicate is not my answer and I just need to maintain a
separate array and do some manual checking for duplicates.
On Tue, Feb 26, 2008 at 7:20 PM, Philip Bridson
<email@hidden> wrote:
Hi there,
It will only return results from itself.
Its like the classic example of employee and department. If you
had a table
that you wanted to link to a list of employees you would bind to
the
employee array controller and vice versa for the department one.
You cannot
bind against the department controller for the value of, for
example,
"Employee Name". All the predicate does is filters the list based
on what
you want. e.g all employee with the name Joe. All you have to do
is set the
exact predicate in the object that you are going to bind against:
- (NSPredicate *)predicate
{
NSString *salaryLimit = @"10000";
NSPredicate *predicate = [NSPredicate predicateWithFormat
@"salary > %@",
salaryLimit];
return predicate;
}
Then when you bind your filter predicate to this method in your
file owner
the array will only return objects that have a value of 10000 set
in their
salary limit key.
I hope I have been of assistance.
Good luck,
Phil.
On 27 Feb 2008, at 00:01, Adam Gerson wrote:
I did look into NSPredicate and the Predicate Programming Guide. I
understand the concept of filtering the ArrayController. I just
didn't
know how to write en expression asking for all unique values from
the
ArrayController for a given key. In the Predicate examples they
filter
a single potential result against some criteria. Can I say "only
return unique values from yourself"?
Adam
On Tue, Feb 26, 2008 at 6:03 PM, Philip Bridson
<email@hidden> wrote:
Yeah there is.
From the documentation:
You can set a predicate for an array controller to filter the
content array.
You can set the predicate in code (using setFilterPredicate:).
You can also
bind the array controller's filterPredicate binding to a method
that returns
an NSPredicate object. The object that implements the method may
be the
File's Owner or another controller object. If you change the
predicate,
remember that you must do so in a key-value observing compliant
way (see
Key-Value Observing Programming Guide) so that the array
controller updates
itself accordingly.
You can also bind the predicate binding of an NSSearchField
object to the
filterPredicate of an array controller. A search field's
predicate binding
is a multivalue binding, described in Binding Types.
Or simply, create a small method in a object, such as the file
owner, that
returns a NSPredicate. Then bind the controller's filter
predicate to the
file owners predicate method. This will automatically filter your
controllers values.
Hope this helps.
Phil.
On 26 Feb 2008, at 22:00, Adam Gerson wrote:
I have a core data object. I would like to populate a TableView
with
only the unique entires for a specific property. Clearly I could
filter the results in code, I was wondering if there was away for
core
data and bindings to do it.
Adam
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