CODEWITHSUNDEEP
c#.netlinq
Simsons
Simsons

Reputation: 12745

Why StringComparison.InvariantCultureIgnoreCase throws exception in where clause

I am trying to do a string compassion as below:

var nDetails = listOfServiceUrls.Where(x => String.Equals(x.Description,  
serviceName,StringComparison.InvariantCultureIgnoreCase));

But getting exception,

System.ArgumentException: Incorrect number of arguments supplied for call to method 'Boolean Equals(System.String, System.String, System.StringComparison)'

If I remove the where clause it works just fine!!

 var nDetails = listOfServiceUrls.Where(x => String.Equals(x.Description,serviceName));

Upvotes: 1

Views: 2079

Answers (2)

Kirill Shlenskiy
Kirill Shlenskiy

Reputation: 9587

You must be using Entity Framework or similar technology which actually needs to interpret the expression supplied as an argument to the Where method. It will only have translations a small subset of Base Class Library (standard .NET lib) methods and their overloads.

Hover your cursor over your listOfServiceUrls variable in the code editor and see what type it is. My money is on the fact that it's IQueryable<string> (as opposed to IEnumerable<string>).

EF does appear to have a translation for the instance Equals(string, StringComparison) method on System.String, so you can rewrite your code as follows:

var nDetails = listOfServiceUrls.Where(
    x => x.Description.Equals(serviceName, StringComparison.InvariantCultureIgnoreCase));

Unlike .NET you will not see a NullReferenceException if any of the strings in the collection happens to be NULL - because the predicate will be executed by SQL Server as opposed to the .NET runtime.

Upvotes: 5

Noctis
Noctis

Reputation: 11763

According to Linqpad, it works flawlessly ... :

List<string> listOfServiceUrls = new List<string>{"one","two","three"};

var nDetails = listOfServiceUrls.Where(x => String.Equals(x,  
"Two",StringComparison.InvariantCultureIgnoreCase));

nDetails.Dump();

Returns: two.

Removing the ignore case will return nothing (since obviously, Two != two .

Upvotes: 0

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