Expression to find parent's without children

From: Robert Bose (Robert.Bos..ntero.com)
Date: Wed Feb 23 2005 - 13:04:41 EST

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    I have a situation where we have a parent object with a flattened
    relationship to a child table (so there is a cross-reference table in
    between).

    So A -> B -> C where A is the parent, B is the flattened x-ref table,
    and C is the child. The object representation looks like A -> C.

    I'm trying to write a expression to return all the A's which do not have
    any
    C's. I tried both:

    ExpressionFactory.matchExp(A.C's_PROPERTY, null)

    And

    new ASTEqual(new ASTObjPath(A.C's_PROPERTY), null)

    neither of which seem to work. What I'd really like to do is check if
    the count of C's is zero or something, but I'm not sure how you would
    even construct that expression.

    Anyone have an idea what works for this?

    Thanks
    Rob

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