trying to call a method in the where of a linq statment

Question

Below is the code I'm using but it replies with

Method 'Boolean isUser(System.String)' has no supported translation to SQL.

Any help? Btw I'm using linq to SQL data source

public void dataBind()
{
    using (var gp = new GreatPlainsDataContext())
    {
        var emp = from x in gp.Employees
                  let k = isUser(x.ID)
                  where x.ActivtyStatus == 0
                  && isUser(x.ID) != false
                  orderby x.ID
                  select new
                  {
                      ID = x.ID,
                      Name = x.FirstName + " " + x.MiddleName
                  };
        ListView1.DataSource = emp;
        ListView1.DataBind();
    }
}

public static bool isUser(string ID)
{
    int temp;
    bool x = int.TryParse(ID, out temp);
    return x;
}

I found a solution to query the result of the first query as objects but is that good cause I will passing through my data twice.

---

the updated code that worked in the end after using the like as advised by Anders Abel

public void dataBind()
    {
        using (var gp = new GreatPlainsDataContext())
        {
            var emp = from x in gp.Employees
                      where x.ActivtyStatus == 0
                      && SqlMethods.Like(x.ID, "[0-9]%")
                      orderby x.ID
                      select new
                      {
                          ID = x.ID,
                          Name = x.FirstName + " " + x.MiddleName
                      };
            ListView1.DataSource = emp;
            ListView1.DataBind();
        }
    }

Answer 1

Linq-to-sql translates the query into SQL. It only knows how to translate a limited set of built in functions. You have to rewrite your query to not include a function of your own.

A complete list of the linq-to-sql supported functions and operators can be found at MSDN.

You can use SqlMethods.Like() to check if the field only contains digits. See T-SQL IsNumeric() and Linq-to-SQL for an example.

Answer 2

The problem you're having is that because the query needs to be ran on the database, you can only use things that will work on the database, the C# code in your isUser method can't run on the database.

You'll have to re-write it without using that function. Perhaps you have a table listing users by IDs you could join on?