From Dwayne Wright PMP
Certified FileMaker Developer
As you likely know, there is a relationship setting that allows you to create child key records from a parent record on the fly. For the most part, this is used in a situation where you can add a new related record by adding information in one of the fields in the last empty portal row.
So when you think about it, that automatically created and linked related record must auto enter the correct information in the child key field for the relationship to be valid.
Although the setting may be in place, the auto create action can break for any number of reasons. The one I’m discussing here is based upon on what type of field you are using in the child table.
Once again, in the situation above, FileMaker enters data in a new related record and places a matching data string into the child key field? What if the field is a calculation field? You can’t type, paste, replace or use the set command on calculation fields can you?
So you can see why it would break.
Why would someone ever make the mistake of creating a child key field as a calculation? They wouldn't intentionally but they may not realize it is a key field. If the original developer doesn't adopt a solid naming convention for the fields, they or the developer that comes after might not realize the impact of the changes they are making.
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