Question

Using LINQ to Entities with Entity Framework and C#:

I have a method that is called CanInactivateReason which checks that there are no active associated records before allowing the user to inactivate the reason. If the method returns false – then a ‘DisabledDelete’ image is displayed with a tooltip informing the user why they are unable to remove the entity in the grid instead of a ‘Delete’ image button. My problem is performance where the queries are returning all related objects instead of doing a top 1 for each navigation property.

.Take(1) extension method is not adding top(1) to my LINQ to Entities query – why??

Nor is .Count() > 0 or .Any() or .Take(1).ToArray().Any() or .FirstOrDefault() != null

Here is my method that returns bool so I’d rather the queries be top 1 – I tried each item below:

    public bool CanInactivateReason(Reason reasonToInactivate)
    {
        bool canInactivate = true;

        if (reasonToInactivate.ProductReasons.Select(pa => pa).Where(pa => pa.Inactive == false).Count() > 0)
        {
            canInactivate = false; // Still active products associated
        }

        if (reasonToInactivate.EnhancementReasons.Select(ea => ea).Where(ea => ea.Inactive == false).Any())
        {
            canInactivate = false; // Still active enhancements associated
        }

        if (reasonToInactivate.SuggestionReasons.Select(sa => sa).Where(sa => sa.Inactive == false).Take(1).ToArray().Any())
        {
            canInactivate = false; // still active suggestions associated
        }

        if ((reasonToInactivate.SessionProductReasons.Select(spr => spr).Where(spr => spr.Inactive == false).FirstOrDefault()) != null)
        {
            canInactivate = false; // Still active sessions associated
        }
        return canInactivate;
    }

I am assuming this is due to accessing the related entities of my object, but what can I do to turn those queries into SQL generated top(1)?

Thanks in advance!

Answer 1

Working via navigation properties like this can cause issues. Depends on how you have LazyLoading configured, what your underlying model is (e.g. use of inheritance associations) and what the base query for reasonToInactivate is.

As a starting point I’d advise going back to basics with the query – just to prove the concept.

So something like (depending on your schema):

if(context.SuggestionReasonsEntitySet.Any(p => p.ReasonId == reasonToActivateId && p.IsActive)) 
{
    canInactivate = false; // Still active enhancements associated
}

So side step the navigation property entirely. Navigation properties can be great, but they can also obscure what should be very simple queries. Personally I stick to them for select queries (i.e. to avoid having to do joins when creating a projection), but avoid them for filtering logic – just because I’ve been bitten a few times like this when using inheritance associations.

If that works then you can try working back towards your navigation property solution to find the point at which things go wrong.

If this isn’t helpful – is the generated SQL from your queries above short enough to post (and be understood)? If so can you post it?