LINQ 到实体 - LINQ 到实体无法识别方法“双重解析（System.String）”方法

Question

Here is my c# codes:

double amount_dbl = double.Parse("0.00001167");

using (Crypto_Shuffler_Entities entities = new Crypto_Shuffler_Entities())
{
    double amount_dbl = double.Parse("0.00001167");

    var order = (from Order in entities.Orders
                 where Order.BTC_Address == "123" && double.Parse(Order.BTC_Amount) == amount_dbl
                 select Order).FirstOrDefault();
    if (order != null)
    {
    }
}

BTC_Amount in sql server is string.
I really do n't know why i have such this error:

LINQ to Entities does not recognize the method 'Double Parse(System.String)' method, and this method cannot be translated into a store expression.

Please give me a solution for both QUERY & METHOD ways of LINQ.

Answer 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.