LINQ to Entities does not recognize the method 'Boolean Contains[Decimal] - asp.net-mvc

Question

I am new to LINQ, so I am pretty confused here. I have a database and try to run following code.
IQueryable<decimal> location_ids = (from m in _db.Admins
where m.UserId.Equals("c5d3dc0e-81e6-4d6b-a9c3-faa802e10b7d")
select m.LocationId);
if (!location_ids.Contains(new Decimal(conf.umisteni.Budova.ID)))
On the if statement I get an error I don't understand, nor do I know, how to solve it:
System.NotSupportedException: LINQ to Entities does not recognize the method 'Boolean Contains[Decimal](System.Linq.IQueryable`1[System.Decimal], System.Decimal)' method, and this method cannot be translated into a store expression.
at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.DefaultTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
Any ideas?

Answer 1

Using Linq-to-Objects IEnumerable will let you use Contains(Decimal) on the result of the query.
IEnumerable<decimal> location_ids = (from m in _db.Admins
where m.UserId.Equals("c5d3dc0e-81e6-4d6b-a9c3-faa802e10b7d")
select m.LocationId);
However, why not just expand the where clause:
IEnumerable<decimal> location_ids = (from m in _db.Admins
where m.UserId.Equals("c5d3dc0e-81e6-4d6b-a9c3-faa802e10b7d") && (m.LocationId == conf.umisteni.Budova.ID)
select m.LocationId);
if (!location_ids.Any())

Answer 2

Linq 2 sql cannot translate the ids.Contains() method to sql.
You could do the following:
if(!location_ids.ToList().Contains(new Decimal(conf.umisteni.Budova.ID)))
This will trigger the sql query, put them in objects and do the contains locally.
Another solution would be to put the conf.umisteni.Budova.Id in the Where clauses (with an equals, not a contains) and then add .any
if((from m in _db.Admins
where m.UserId.Equals(conf.umisteni.Budova.ID.ToString())
select m.LocationId).Any())
This would only be a good idea if you don't need any of the keys afterwards off course.

Answer 3

Here is a helper method that provides all of the goodness of .Contains() in the context of Linq to Entities
public static class LinqToEntitiesUtil
{
/// <summary>
/// Extension method that enables .Contains(obj) like functionality for Linq to Entities.
///
/// Source: http://www.velocityreviews.com/forums/t645784-linq-where-clause.html
/// </summary>
/// <typeparam name="TElement">The element being evaluated by the Where clause</typeparam>
/// <typeparam name="TValue">The value to match</typeparam>
/// <param name="valueSelector">Lamda for selecting matching values</param>
/// <param name="values">IEnumerable of the values</param>
/// <returns>Expression consumable by Linq to Entities that reflects semantics of .Contains(value)</returns>
/// <remarks>
/// Usage:
///
/// Replace expression like
///
/// where ChildrenIDs.Contains(items.CategoryID)
///
/// with
///
/// .Where((BuildContainsExpression<Item, int>(item => item.CategoryID, ChildrenIDs))
///
/// NOTE: If the item collection is large, the SQL query will be as well.
/// </remarks>
static public Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values)
{
if (null == valueSelector)
{
throw new ArgumentNullException("valueSelector");
}
if (null == values) { throw new ArgumentNullException("values"); }
ParameterExpression p = valueSelector.Parameters.Single();
if (!values.Any())
{
return e => false;
}
var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue))));
var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));
return Expression.Lambda<Func<TElement, bool>>(body, p);
}
}

Answer 4

I just got bit by something similar. Your System.Data.dll might not be the same version. The method was supported on my dev machine, but then I got runtime errors when I deployed to a test machine. The System.Data.dll version was older. Backwards compatible methods are a good fix. But I would still want to track down the discrepancy, some patch must be applied that didn't on the other environments. Who knows what other issues this will cause down the road if left unchecked.