Create record in related table *only* if not previously existing there - filemaker

Question

I have a Filemaker database with a Members table, an Events table, and a join table called Attendance which should list which members attended which events. Attendance has the setting "allow creation of new records" ticked for Members (doesn't need it for Events).
Data arrives in an Excel spreadsheet for importing to Attendance. But then I want to see if there are people attending who aren't in our records already... sort of like this:
look at each of the newly added records in the attendance table
see if the members mentioned there exist in the member table
if so, do nothing
else create a new record in the member table for them, using data from the attendance table.
If I'm understanding it correctly, Steps 3 and 4 should look something like this:
Set Variable [ $fname; Value: Attendance::firstname ]
Go To Layout ["Member" (Firstname)]
New Record/Request
Set Field [Member::Firstname; $fname]
i.e. put the desired info into variables, start a new record in the related table and set the data there to the value of the variables.
But how do I get step 2 happening? I'm guessing some sort of loop will go through the found set of records in Attendance, and grab the relevant identifier. How do I show that to the Member table to see if it's present or not?

Answer 1

"Firstname" might be a bit light to pinpoint a unique member, if you have many members !
I'd presume therefore you would have some sort of unique key for each member.
As from there, just search for the member in the member base, before creating the new record…

Answer 2

Link the two tables with an EQUALS relationship.
Write a script:
// Loop through your attendance records.
// Be sure you're in the correct layout
Go to Layout ["imported list"]
// Attempt to go to the membership record of the person who is attending the event.
Go to Related Record [Show only records from: from table: "membership table"; using layout: "membership table"
// If the person who is attending IS in the membership list, you'll go to that member's record in the "membership table."
// If the person who is attending is NOT in the membership list, you'll get an error. You can use that error in an if statement to execute code to add that member.
If [Get ( LastError ) = "101"]
// insert code to add new member
End if

Answer 3

Since you already have a relationship between Member and Attendance, it means that you can "see" any related Members from the Attendance table across the relationship.
We also know that you only need to evaluate the new attendance records coming in from your spreadsheet.
I also assume that there could possibly be be more than one attendance record per Member in the spreadsheet. This may not be the case, but it's safer to assume it's possible.
I'm also assuming that you are linking the Member table to the Attendance table via the primary key in Members and a foreign key in Attendance, i.e. Member::ID = Attendance::Member ID.
So here's the script process I suggest:
Import the new Attendance record into the Attendance table.
This will give you a found set of only new attendance records
From the Attendance layout, perform a find for related Member records with an omit, i.e.:
# This assumes you're already on the Attendance layout
Enter Find Mode
Set field [Member::ID ; "*"]
Omit record
Constrain Find
This will give you a found set of new Attendance records that do not have matching Member records.
From here you could loop through each of the attendance records and create the Member records as needed.
If you check the Allow creation on the Member side of the Member -< Attendance relationship, you could set the field in the Member table directly from the Attendance layout.
Since the 1 to Many relationship between Member and Attendance goes 1=Member Many=Attendance, you would need to check to be sure you haven't already created a Member record during your loop, i.e. If a new Member had multiple Attendance records you could have already created a Member record during the loop.
Your loop would look like this:
Go to Record [First]
Loop
If [IsEmpty(Member::ID)]
Set Field [Member::First Name] // This first Set Field will create your new Member Record as long as the "Allow Creation" is enabled on the Member side
Set Field [Member::Last Name]
... This would be the rest of your set field steps for Member
End If
Go to Record [Next ; Exit After Last]
End Loop
This way you don't need to navigate away from your Attendance record set. Also, the Primary and Foreign keys for both tables will be created and set automatically through the attributes of the relationship itself.