public override FdbAsyncIterator <TSource> Where(Func <TSource, bool> predicate)
{
return(FdbAsyncEnumerable.Filter <TSource>(
m_source,
m_filter.AndAlso(new AsyncFilterExpression <TSource>(predicate))
));
}
public override FdbAsyncIterator <TResult> Where(Func <TResult, bool> predicate)
{
if (predicate == null)
{
throw new ArgumentNullException("predicate");
}
// note: the only possible optimization here is if TSource == TResult, then we can combine both predicates
// remember: limit/offset are applied AFTER the filtering, so can only combine if they are null
// also, since transform is done after filtering, we can only optimize if transform is null (not allowed!) or the identity function
if (m_limit == null &&
(m_offset == null || m_offset.Value == 0) &&
typeof(TSource) == typeof(TResult) && //BUGBUG: type comparison maybe should check derived classes also ?
m_transform.IsIdentity())
{
var filter = new AsyncFilterExpression <TSource>((Func <TSource, bool>)(Delegate) predicate);
if (m_filter != null)
{
filter = m_filter.AndAlso(filter);
}
//BUGBUG: if the query already has a select, it should be evaluated BEFORE the new filter,
// but currently FdbWhereSelectAsyncIterator<> filters before transformations !
return(new FdbWhereSelectAsyncIterator <TSource, TResult>(
m_source,
filter,
m_transform,
m_limit,
m_offset
));
}
// no easy optimization...
return(base.Where(predicate));
}