Hi,
I know that the XQUF prohibits it, but for writing robust functions, it is often necessary to mix query and update/docmgmt functionality. Some examples:
* Expression that queries/updates document, but if the document does not exist, adds an empty version of it: let $name := "foo.xml" let $emptydoc := <root/> let $doc := if (empty(pf:documents()[.=$name])) then (put($emptydoc,$name),$emptydoc) else doc("foo.xml") return $doc//bar * Expression that adds to a log-file: let $log := doc("log.xml") let $expr := ...some expression... return (do insert <entry>...{$expr}...<entry> as last into $log,$expr)
Each of these patterns gives you a "!type error: err:XUST0101: illegal mix of updating and non-updating expressions" error.
Isn't is possible to somehow allow such expressions? It is against the standard, so it probably requires some server configuration parameter, but it would be really really useful to have it. Mixing queries with update/docmgmt is known to cause many semantical problems, but only if these updates are visible within the query. Looking at the implementation based on pending update lists, then each of these patterns is harmless. If you declare that no updates are visible within the transaction (which is against the standard), then allowing these queries is I guess not hard: it simply means that with updating expressions and document management expressions you do return a result.
Another thing I've been thinking about in this context: If I send two SOAP-messages to a server on its XRPC-port, am I guaranteed that they are served in the same order? I could perhaps, with a lot of duplication of code, separate update/docmgmt from a query, i.e., implement these things with two requests to the server. I really dislike such a solution, though.
Looking forward to comments :-)
Maurice.