Question

Can somebody please give an explanation to why I am getting this error with my LINQ code?

LINQ to Entities does not recognize the method ‘System.String
GenerateHashWithSalt(System.String, System.String)’method and this
method cannot be translated into a store expression.

var query = (from u in context.Users
                         where 
                         u.Password ==  
                          GenerateHashWithSalt(password, GetUserID(username))
                         select u).Count();

Answer 1

You are trying to pass a method to EF which tries to convert that method to known SQL command.
SQL doesn’t know about GenerateHashWithSalt(System.String, System.String)
You should first assign the result to a variable then generate your Linq to Entity Query.

Example

var hashedPassword = GenerateHashWithSalt(password, GetUserID(username));
var user = (from p in Users
        where p.Password == hashedPassword
        select p).FirstOrDefault();