Custom function parameter referencing field in foreign file?

[Kent Searight]

Hi all,

I'm trying to write a Custom Function in FM Dev7 that has a parameter that references a field in a related table but of a different file. I'll bet there's a way of doing it but I can't figure it out for the life of me. Can someone clue me in, please?

Thanks in advance for your help! :)

[Ender]

In a custom function, the parameters are placeholders that will have values at the time the function is called. When calling a CF from within a calculation, you can pass static values, local field values, or related field values the same way as any built-in function:

MyField (calculation, text result) = MyFunction ( SomeTable::SomeField )

To use any field values within a custom function, you must pass them as parameters to the CF.

[Kent Searight]

Hi Ender. Thanks for the quick response. The problem I run in to is that a parameter in CF's can't contain colons, among other things, therefore MyFunction ( SomeTable::SomeField ) won't work. Am I missing something in your answer?

[Ender]

As I said, the parameters are placeholders. Use non-reserved words for the parameters, and remember that they are local to that function:

Let's say we define a simple CF to return the nth character from a string of text. The CF would look something like:

charN ( text ; n ) =

middle ( text ; n ; 1 )

note that "text" is the name of the first parameter and "n" is the name of the second parameter. These parameters have nothing to do with real field names. They are temporary placeholders that will be populated when the function is called and something is passed to those parameters.

In a calculation we could use this function by passing fields as the parameters, or we might pass a text string and a number:

MiddleInitial (calculation, text result) = charN ( MiddleName ; 1)

or

RandomLetter (calculation, text result) = charN ( "ABCDEFGHIJKLMNOPQRSTUVWXYZ" ; int ( Random * 26 ) )

The point is, the CF definition does not have any references to fields in your database. It only knows about values you send in as parameters.

[Kent Searight]

Oookay, I finally get it now! It's funny how sometimes you can get stuck on one track and not be able to see outside of it. In the dozen or so CF's I've written thus far I've always ensured that the parameter in the CF was a legit field name in the tables it would be used in. This worked fine until I wanted to create a parameter that was specifically the name "Table::fieldName" instead of just "fieldName", which as I said would be an actual field name.

So, I guess that my question changes a bit at this point. And please bear with me...since the parameter is just a placeholder, and doesn't necessarily reference a field name (although it can, which makes it very flexible and easy to use), can you think of a way for me to create a parameter or a calc that will add "Table::" onto the parameter's name, so that when I use that in a calc the only thing I have to do is insert it into the calc and click OK, and it'll work from there?

[Ender]

No, you will need to type the related field names into the CF calls.

I think the mistake you are making is that you are assuming your CF should be used only by one field. The CF should be written more generally so it can be used anywhere. This includes giving the parameters descriptive yet general names--not specific field names.

[Kent Searight]

I see what you're saying about writing it more generally. I was definitely missing the bigger picture in that respect, as I was always writing it for one or more specific fields.

Thanks a bunch for all your help!!!