[xsd-users] Schema caching example: enabe schema caching automatically

[Boris Kolpackov]

Hi Ashish,

Ashish Singhal <ashish at ashishsinghal.com> writes:

> Are there any hooks for configuring the xerces-c parser used for loading
> xml to cache the schema automatically?
> 
> I had a look at the schema caching example supplied with xsd and it works,
> but it ends up being a 2 stage process:
> 
> 1) load the xml schema using xerces-c (with the caching parser)
> 2) construct the xsd generated object.
> 
> I'd like to skip #1 and have it done automatically by xsd generated code.

Normally, the idea behind schema caching is that you want to do it once
and then reuse the grammar to parse multiple documents. And to achieve
this, you need to reuse the XML parser. On the other hand, the generated
parsing functions create a new XML parser for every invocation, so even
if there were a way to configure the parser used, it would be destroyed
at the end of the call. That's why to do caching you need to have your
own XML-to-DOM stage. This way you can make sure the same parser is used,
in some application-specific way.


> The 2 stage process is inconvenient, as I have a significant amount of code
> that loads xml files using the generated constructors. It would be
> difficult to change everything to the two stage loading process.

You can always wrap the generated parsing functions (I assume that's
what you mean by "generated constructors") and hide all the schema
caching. You will need to make sure that they all use a single
parser in some way (e.g., a global parser for a single-threaded
application and maybe TLS for multi-threaded). You could probably
even make this wrapper a function template.

Note also that it is possible to tell Xerces-C++ to load and cache
the schemas automatically, as it parses XML documents that reference
them instead of pre-loading them manually at the beginning.

Boris