Craig

If you are defining a Parent-Child Relationship with Default Storage the global structure of the child with change from ^child(id) to ^child(parentid,id) so you will not see any of the old data, no hint will fix that issue, sorry.

If your current child data is valid and you want to keep it I would suggest defining a Foreign Key constraint with Cascade on Delete.  This will keep the global structure the same but let you enforce your relationship.

Nice clear description Benjamin.  This should be a big help for query performance.  It is such a common problem in support when we have to help customers deal with outliers.  Now the RTPC should do that work for them!

So there is a zip file attached to this article that contains a bunch of examples.  the Class Mapping.ChildPiece should be close to what you need.  the global for that class Parent Child looks like this:

/// ^Par(1)=Parent1\Child11#child12#child13
///      2)=Parent2\Child21#child22
///      3)=Parent3
/// 

and the mapping for the child is:

<SQLMap name="Map1">
<Data name="ChildData">
<Delimiter>"^"</Delimiter>
<Piece>1</Piece>
</Data>
<Global>^Par</Global>
<RowReference>$P($P(^Par({L1}),"\",2),"#",{L2})</RowReference>
<Subscript name="1">
<Expression>{Mapping.ParentPiece.Sub1}</Expression>
</Subscript>
<Subscript name="2">
<AccessType>Piece</AccessType>
<Delimiter>"#"</Delimiter>
<Expression>{PieceCounter}</Expression>
<Invalidcondition name="1">
<Expression>$P(^Par({L1}),"\",2)=""</Expression>
</Invalidcondition>
</Subscript>
<Type>data</Type>
</SQLMap>

If you can get your working let me know and I can make an example for your global.

Brendan