Not sure if there is already some other mechanism in place for this... ...but it would be neat if it was possible to intercept whatever the dataservice framework adds to IQueryables exposed by data services before enumerating them. If a filter, sort, paging or something else is added server side or as a result of a user request I may want to apply additional rules and/or change how this is added to the query. Especially on IQueryables with large underlying sets of data and/or a complex base query it can be important to be able to control filters and sorting to avoid having users kill the underlying database...

Maybe something along the lines of:

[QueryFilterInterceptorEx("Orders")]
public IQueryable<Order> OnQueryFilterOrders(IQueryable<Order> baseQuery, Expression<Func<Order, bool>> filterExpression)
{
if (expression.FindMemberExpression("SomeMemberName"))
{
return baseQuery.Where(filterExpression).Where(f => f.SomeAdditionalFilter == 123);
}
else
{
return baseQuery.Where(filterExpression);
}
}

[QuerySortInterceptorEx("Orders")]
public IQueryable<Order> OnQuerySortOrders(IQueryable<Order> baseQuery, Expression<Func<Order, TKey>> sortExpression)
{
if (sortExpression.Body is MemberExpression
&& ((MemberExpression)sortExpression.Body).Member.Name == "SomeMember")
{
return (IQueryable<Order>)baseQuery.OrderBy(sortExpression);
}
else
{
return (IQueryable<Order>)baseQuery.AsEnumerable().OrderBy(sortExpression);
}
}

(also see this related forum thread: http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataservices/thread/d853d6f2-c1f1-4acc-9657-cc575dec2d03 )