Question

I have a problem getting result from a database by specific column value using LINQ.

This is my table Customer(Id, Name, Surname, ExternalID). ExternalID is a varchar column with specific string pattern, for instance 01_johnDoe.

Let’s say that I want to get customer johnDoe and my mehod gets string johnDoe.

I’m able to do that by this way :

public<Customer> GetMeACustomer(string customerExternalID)
{
using(var context=new MyContext())
{

var customerObject=(from c in contex.Customer where c.ExternalID.Contains(customerExternalID)).Single()   

}

}

This code is not good enough simply because query sent to Database is using operator LIKE. This is slow (I have huge number of customer).
I couldn’t implement inside linq something like this :

   var example = ExternalIDFromDatabase.Substring(ExternalIDFromDatabase.IndexOf("_") + 1, customerExternalID.Count());

by this code I could simply say

var customerObject=(from c in contex.Customer where c.ExternalID.Substring(c.ExternalID.IndexOf("_") + 1, customerExternalID.Count())==customerExternalID).Single()

But it’s not working.
Any Ideas ?
Than you

Answer 1

It should work when you replace customerExternalID.Count() with customerExternalID.Length or when you create local variable (let say customerExternalIDCount) and assign count to it. Probably provider tries to translate this Count call into SQL.

BTW you probably want to use Substring method without specifing length. If there was for example 01_johnRobin and 02_johnRobins in database, you would get 2 results for johnRobin customerExternalID.