SQL Server : count XML Children within Parent - sql

Question

Hi I have been looking for a way of updating xml produced in sql to add the count of child nodes and add the count to the parent node using SQL
I've tried various workings around
SET #xml.modify
(
'insert attribute TrCount {count(/XML/Acs/Act/Trs/Tr)} into (./XML/Acts/Act/Trs)'
);
<XML>
<Id>12</Id>
<DateCreated>2013-04-11</DateCreated>
<Acts AccountCount="4">
<Act RowID="1>
<Trs>
<Tr RowID="1" />
</Trs>
</Act>
<Act RowID="2">
<Trs>
<Tr RowID="1" />
<Tr RowID="2" />
</Trs>
</Act>
<Act RowID="3">
<Trs>
<Tr RowID="1"/>
</Trs>
</Act>
<Act RowID="4">
<Trs>
<Tr RowID="1" />
<Tr RowID="2" />
<Tr RowID="3" />
<Tr RowID="4" />
<Tr RowID="5" />
<Tr RowID="6" />
<Tr RowID="7" />
</Trs>
</Act>
</Acts>
</XML>
above is a sample, I have got it to give me a count of within but I can not seem to get a count of each within each , so the result would look like
<Act RowID="1>
<Trs Trcount="1">
<Tr RowID="1" />
</Trs>
</Act>
<Act RowID="2">
<Trs Trcount="2">
<Tr RowID="1" />
<Tr RowID="2" />
</Trs>
</Act>
<Act RowID="3">
<Trs Trcount="1">
<Tr RowID="1"/>
</Trs>
</Act>
<Act RowID="4">
<Trs Trcount="7">
<Tr RowID="1" />
<Tr RowID="2" />
<Tr RowID="3" />
<Tr RowID="4" />
<Tr RowID="5" />
<Tr RowID="6" />
<Tr RowID="7" />
</Trs>
Cheers

Answer 1

Try something like this, which assumes each Act contains only one Trs:
declare #count int = #xml.value('count(/XML/Acts/Act)', 'int'),
#counter int = 1;
while (#counter <= #count)
begin
SET #xml.modify ('insert attribute TrCount {count(/XML/Acts/Act[sql:variable("#counter")]/Trs/Tr)} into (/XML/Acts/Act[sql:variable("#counter")]/Trs)[1]');
set #counter += 1;
end
insert() can only modify a singleton, not a whole set of nodes in one go.