Case insensitive string compare in LINQ-to-SQL

Question

I've read that it's unwise to use ToUpper and ToLower to perform case-insensitive string comparisons, but I see no alternative when it comes to LINQ-to-SQL. The ignoreCase and CompareOptions arguments of String.Compare are ignored by LINQ-to-SQL (if you're using a case-sensitive database, you get a case-sensitive comparison even if you ask for a case-insensitive comparison). Is ToLower or ToUpper the best option here? Is one better than the other? I thought I read somewhere that ToUpper was better, but I don't know if that applies here. (I'm doing a lot of code reviews and everyone is using ToLower.)

Dim s = From row In context.Table Where String.Compare(row.Name, "test", StringComparison.InvariantCultureIgnoreCase) = 0

This translates to an SQL query that simply compares row.Name with "test" and will not return "Test" and "TEST" on a case-sensitive database.

Answer 1

Sometimes value stored in Database could contain spaces so running this could be fail

String.Equals(row.Name, "test", StringComparison.OrdinalIgnoreCase)

Solution to this problems is to remove space then convert its case then select like this

 return db.UsersTBs.Where(x => x.title.ToString().ToLower().Replace(" ",string.Empty).Equals(customname.ToLower())).FirstOrDefault();

Note in this case

customname is value to match with Database value

UsersTBs is class

title is the Database column

Answer 2

I used System.Data.Linq.SqlClient.SqlMethods.Like(row.Name, "test") in my query.

This performs a case-insensitive comparison.

Answer 3

Remember that there is a difference between whether the query works and whether it works efficiently! A LINQ statement gets converted to T-SQL when the target of the statement is SQL Server, so you need to think about the T-SQL that would be produced.

Using String.Equals will most likely (I am guessing) bring back all of the rows from SQL Server and then do the comparison in .NET, because it is a .NET expression that cannot be translated into T-SQL.

In other words using an expression will increase your data access and remove your ability to make use of indexes. It will work on small tables and you won't notice the difference. On a large table it could perform very badly.

That's one of the problems that exists with LINQ; people no longer think about how the statements they write will be fulfilled.

In this case there isn't a way to do what you want without using an expression - not even in T-SQL. Therefore you may not be able to do this more efficiently. Even the T-SQL answer given above (using variables with collation) will most likely result in indexes being ignored, but if it is a big table then it is worth running the statement and looking at the execution plan to see if an index was used.

Answer 4

The following 2-stage approach works for me (VS2010, ASP.NET MVC3, SQL Server 2008, Linq to SQL):

result = entRepos.FindAllEntities()
    .Where(e => e.EntitySearchText.Contains(item));

if (caseSensitive)
{
    result = result
        .Where(e => e.EntitySearchText.IndexOf(item, System.StringComparison.CurrentCulture) >= 0);
}

Answer 5

I tried this using Lambda expression, and it worked.

List<MyList>.Any (x => (String.Equals(x.Name, name, StringComparison.OrdinalIgnoreCase)) && (x.Type == qbType) );

Answer 6

As you say, there are some important differences between ToUpper and ToLower, and only one is dependably accurate when you're trying to do case insensitive equality checks.

Ideally, the best way to do a case-insensitive equality check is:

String.Equals(row.Name, "test", StringComparison.OrdinalIgnoreCase)

Note the OrdinalIgnoreCase to make it security-safe. But exactly the type of case (in)sensitive check you use depends on what your purposes is. But in general use Equals for equality checks and Compare when you're sorting, and then pick the right StringComparison for the job.

Michael Kaplan (a recognized authority on culture and character handling such as this) has relevant posts on ToUpper vs. ToLower:

• http://www.siao2.com/2007/10/01/5218976.aspx
• http://www.siao2.com/2005/03/10/391564.aspx

He says "String.ToUpper – Use ToUpper rather than ToLower, and specify InvariantCulture in order to pick up OS casing rules"