I am using the example in the filemaker book about using XML script parameters with the custom function GetParamXML to retrieve them. I am currently trying to make a button that will add a record to a join table, and I want to check to see if the record already exists in the table before I add it.

The way I am currently trying to do it, I am doing a perform find where the id of the record matches the parameter passed to the script. The only problem is, I don't think that "Perform Find" allows calculations in the criteria field.

So I guess my question is, how the heck do I do a simple search with data passed from a script parameter?

Maybe you can set a temporary global field with the script parameter and Perform Find based off the global value.

I don't think that "Perform Find" allows calculations in the criteria field.

That is correct. However, Set Field does. So try:

Enter Find Mode [ ] // NOTHING IS CHECKED

Set Field [ yourtable::fieldtosearch ; Get ( ScriptParameter ) // OR WHATEVER CALCULATION YOU NEED

Perform Find [ ]

If you have a relationship from the parent table to the join table based on the parent ID, then you can see if there is a related record without performing a find:

<From the parent table>

If [ isempty(jointable::recordID) ]

#No join record exists

End If

If your criteria for a "record already exists in the table" is more complex than that, you could add a Table Occurence with a multi-criteria relationship, then use the same type of test.