Apple

On 05/05/2010, at 4:17 PM, Johann Werner wrote:

if you want to write your own comparator look at ERXComparisonSupport from Wonder how it should be written. Unfortunately you have to register your comparator for a specific class type (e.g. String.class) so it is used automatically in place of the default comparator but this means you can't specify one for solely your number attribute. Perhaps someone has more ideas?

Thanks Johann.

Maybe "WODisplayGroup" in the subject is turning people off here. :-) Say I just want an EOSortOrdering that can solve this problem:

1. I have an 'Invoice' entity with a 'number' attribute. The attribute's type is VARCHAR. This is completely intentional, as the client may want the "number" to contain letters at some point. (Pretend the attribute name is "identifier" if it hurts your brain. :-)

2. I want to display the Invoice objects in a WODisplayGroup in a custom order. At the moment, that order is simple: all values for Invoice.number are currently actual numbers. So, for now, I want to cast them to integers, and sort them numerically. (This may change later, as letters may be appended.)

3. Using a standard (array of) EOSortOrdering (Invoice.NUMBER.ascs()), the "numbers" are obviously sorted in ASCII order. {1, 10, 11, 2...} For now, what I want is {1, 2, 3, ... 10, 11, ...}.

It only needs to work for in-memory sorts.

What am I missing here? I can write an NSComparator for these number-as-string keys, if that's what's required, but then what do I do with that? What I want is the EOSortOrdering for the WODisplayGroup (don't I?), I don't see where the comparator would fit in.

As a workaround, I can add this to Invoice.java:

public Integer numberAsInteger() {
return new Integer(number());
}

and then pass:

new EOSortOrdering("numberAsInteger", EOSortOrdering.CompareAscending)

to the WODisplayGroup. But that's only going to work while I know the attribute values are integers-as-strings. What I need is to be able to customise the comparison myself to guard against the format of the values changing in the future.

(There's an old thread here:

http://lists.apple.com/archives/webobjects-dev/2004/Oct/msg00271.html

which poses a very similar problem. What I need is for Chuck to expand on his response: "3. Create a new comparator that does what you want." :-) Where do I put that comparator, Chuck?)

I can write the code to do the comparison, I just don't understand how to plumb it all together.

References:
	>Custom EOSortOrdering for a WODisplayGroup (From: Paul Hoadley <email@hidden>)
	>Re: Custom EOSortOrdering for a WODisplayGroup (From: Johann Werner <email@hidden>)