Way to generically iterate through entities in XML? - sql-server

Question

Is there a generic way, in T-SQL, to iterate through an xml variable and get the xml for each entity in turn?
DECLARE #xml xml =
'<Entities>
<Entity key="4" attrib1="abc" attrib2="def" />
<Entity key="18" attrib1="ghi" attrib2="jkl" />
<Entity key="938" attrib1="mno" />
</Entities>'
For example, in the above XML, there are three instances of Entity. I want the XML for each one in turn. I can do this in a hard-coded way, e.g.
SELECT #entityxml = #xml.query('/Entities/Entity[1]')
which will return
<Entity key="4" attrib1="abc" attrib2="def" />
I can then change it to a [2] to get the next one, and so forth.
But, according to both BOL and experimentation, the parameter to #xml.query must be a string literal. In other words, a variable can't be used as the parameter, building it with [1], [2], etc., and getting however many entities there are. It appears we have hard-code the queries, which makes for some ugly code.
I know other methods can be used to get the data in the xml into a table, and then iterate through the rows in the table. I'm specifically asking about getting the XML itself, i.e. getting the equivalent of the above #xml.query, but being able to do so without having to hard-code the array value.
Thanks!

Answer 1

You can use position() to select elements based on index:
DECLARE #xml xml =
'<Entities>
<Entity key="4" attrib1="abc" attrib2="def" />
<Entity key="18" attrib1="ghi" attrib2="jkl" />
<Entity key="938" attrib1="mno" />
</Entities>'
declare #i int;
set #i = 2;
select #xml.query('Entities/Entity[position()=sql:variable("#i")]');

Answer 2

Something like this will do the trick:
DECLARE #xml xml =
'<Entities>
<Entity key="4" attrib1="abc" attrib2="def" />
<Entity key="18" attrib1="ghi" attrib2="jkl" />
<Entity key="938" attrib1="mno" />
</Entities>';
SELECT #xml.query('
for $i in //Entity
return
<Entity>
{ $i/#key }
{ $i/#attrib1 }
{ $i/#attrib2 }
</Entity>
');