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>There is no a performance hog, because VFP evaluates the method for visible rows only.

Every call to the function takes time no matter when it occurs.

>If you use simple relations that grid updating (you go to some dialog change something there and return to firm with grid) is a pain.

I don't understand what you are saying here, but I do know that the column with the UDF will always be read only and can never be edited directly.

>If ChildOrder stuff would be so good, then what's the idea to use p-views?

Did you really want me to answer his? This is like asking, "If table are good why do we have cursors?"