不区分大小写的数组，包含在Linq查询中

Question

I'm trying to use Array.Contains on a string array within a Linq query:

var otherMatchingDevices = from d in selectedDevices
                           from c in mldb.Companies
                           where d.CompanyID == c.CompanyID && c.Deleted == 0
                           where searchTerms.Contains(d.Name.ToString(), StringComparer.CurrentCultureIgnoreCase) || searchTerms.Contains(c.CompanyName.ToString(), StringComparer.CurrentCultureIgnoreCase)
                           select d;

When the query is evaluated it crashes with "Unsupported overload used for query operator 'Contains'.

I tested this code using the StringComparer and it works fine and prints out "fOO":

string[] sList = { "fOO", "bar" };
string[] array = { "foo" };
List<string> stringlist = sList.ToList();
var qry = from s in stringlist
          where array.Contains(s, StringComparer.CurrentCultureIgnoreCase)
          select s;
if (qry.Count() > 0) Console.WriteLine(qry.First().ToString());

Can anyone show me how to use a case insensitive Array.Contains within a Linq query? I do NOT want to convert the original string ToUpper() or ToLower() as it is expensive and it changes the original data.

Answer 1

Your first snippet is invoked using Linq to SQL , this means that it will eventually be translated into SQL. So, whether comparison will be case-sensitive or not depends on the COLLATION of your table column. That's why Linq throws the exception, because it cannot guarantee case-sensitivity.

Your second query snippet is performed using Linq to Objects , hence string equality can be enforced, since the actual string is already in-memory.

Answer 2

I tested this code using the StringComparer and it works fine and prints out "fOO":

LINQ to Objects is different than LINQ to SQL/Entities. The latter needs to convert your query into a SQL expression, hence it doesn't understand what StringComparsion is.

You can use AsEnumerable() on your query to bring the data in-memory:

var otherMatchingDevices = (from d in selectedDevices
                            from c in mldb.Companies
                            where d.CompanyID == c.CompanyID && c.Deleted == 0)
                            .AsEnumerable()
                            .Where(searchTerms.Contains(d.Name.ToString(), 
                                               StringComparer.CurrentCultureIgnoreCase) || 
                                   searchTerms.Contains(c.CompanyName.ToString(), 
                                               StringComparer.CurrentCultureIgnoreCase))
                            .ToArray()