This is an issue that existed with WCF RIA as well - Visual Studio seems to trigger creating the Generated_Code far too often. For example, editing some XAML in the designer, then clicking on the design surface or opening another .xaml file. This happens if there are unsaved changes to any XAML. Saving those changes will also regenerate the OpenRiaServices client code, but then it's possible to move around without the constant rebuilds.
It would seem to me that changing the model or domain service should *maybe* do this, however only if it would include, for example, a new query method in the domain service - but that's not the case, even when the Generated_Code is rebuilt it does not include changes to the Domain Service until the project is built.
We have a fairly large data model (260+ tables, a handful of views and sprocs as well), which results in a generated code file >5MB, and takes a good 6-7 seconds to generate which is a bit frustrating as I don't think it really needs to be doing that when I edit XAML...
Is there any way to control this behavior?