LINQ To Entity - LINQ to Entities does not recognize the method 'Double Parse(System.String)' method

Solution 1:

Having a double value in SQL server as string is questionable. Proably then you might also want to compare it as string without parsing at all. Assuming you would like you to do with parsing, double.Parse() doesn't have a corresponding conversion in EF you could indirectly do it at the client side:

var order = (from Order in entities.Orders
                 where Order.BTC_Address == "123"                  select Order)
           .AsEnumerable()
           .Where(o => double.Parse(o.BTC_Amount) == amount_dbl)
           .FirstOrDefault();

From the point forward you have AsEnumerable(), it is client side.

EDIT: And this is the method way:

var order = entities.Orders
           .Where(Order => Order.BTC_Address == "123") 
           .AsEnumerable()
           .Where(o => double.Parse(o.BTC_Amount) == amount_dbl)
           .FirstOrDefault();

PS: I would directly write the double value instead of parsing from a string as in your example.

PS2: Also don't forget, with a double you are unlikely to get equal values. In SQL server and C# side a decimal is a more appropriate type to use.