Question

Using LINQ to Entities, how can I determine if any item from a List of ints exists in a comma delimited string of ints?

For example, I want to write something like the following (logically):

collection.Where(collection.DelimitedStringOfInts.Contains(listOfInts.AnyOfThem))

Also, I should mention that I’m doing this using LINQ method chaining, with the delimited string as part of the entity –

var listOfInts = GetListOfInts();
var query = from x in Db.Items select x;
if (listOfInts != null && listOfInts.Count() > 0)
{
  query = query.Where(x => x.DelimitedStringOfInts.Contains(listOfInts.AnyOfThem));
}

UPDATE:
Using Alex’s referenced article, I implemented a working solution as follows:

var query = from x in Db.Items select x;
var listOfInts = GetListOfInts();
if (listOfInts != null && listOfInts.Any())
{
    //"ToListOfStrings" is a simple extension method I wrote to create a List<string> from a List<int>
    var delimitedIds = listOfInts.ToListOfStrings(','); 
    query = query.Where(
        BuildOrExpression<DatabaseItem, string>(x => x.DelimitedStringOfInts, delimitedIds)
        );
}

An update was required to the “BuildOrExpression” referenced in the article. The “equals” operator had to be changed to a “contains” operator.

var contains = values.Select(value =>
    (Expression)Expression.Call(
                   valueSelector.Body,
                   typeof(string).GetMethod("Contains"),
                   Expression.Constant(
                           value,
                           typeof(TValue)
                   )
           )
   );

Answer 1

Take a look at this tip, it is not exactly what you are asking for but I think you can tweak it to get what you want.

Alex