Entity Framework: Unable to create a constant value of type 'System.Collections.Generic.IList`1'

Question

This has caused me no end of problems today. I have this simple query

var result =
    DataContext.Accommodations.Where(a => 
        (criteria.MinPrice          


        

Answer 1

The constant value EF can't create is null for the comparison criteria.Locations == null. You need to split the query into two cases and do the check for the empty list outside of the query, for example like so:

var result = DataContext.Accommodations.Where(a => 
    (criteria.MinPrice == null || 
        a.AccommodationRates.Any(r => r.From >= criteria.MinPrice)) &&
    (criteria.MaxPrice == null ||
        a.AccommodationRates.Any(r => r.To <= criteria.MaxPrice)));

if (criteria.Locations != null && criteria.Locations.Count > 0)
{
    result = result.Where(a => a.AccommodationPlaceJoins
        .Any(j => criteria.Locations.Contains(j.Place.PlaceName)));
}

Edit

BTW: Composing the whole query would make it better readable in my opinion and will simplify the SQL that has to be sent to the database:

IQueryable<Accommodation> result = DataContext.Accommodations;

if (criteria.MinPrice != null)
    result = result.Where(a => a.AccommodationRates
        .Any(r => r.From >= criteria.MinPrice));

if (criteria.MaxPrice != null)
    result = result.Where(a => a.AccommodationRates
        .Any(r => r.To <= criteria.MaxPrice));

if (criteria.Locations != null && criteria.Locations.Count > 0)
    result = result.Where(a => a.AccommodationPlaceJoins
        .Any(j => criteria.Locations.Contains(j.Place.PlaceName)));