将null传递到SQL命令

Question

I have a class:

public class Intlist
{
    public int yesFlag{ get; set; }
    public int? noFlag { get; set; }
}

I need to update a database table, but sometimes the value is null for the nullable ints. I am using

CommandText = @"UPDATE thetable 
                SET Yes = " + list.yesFlag +
                   ",NoFlag = " + (list.previous == null) ? DBNull.Value : list.previous +
                   ",NextValue = 10" 

I'm trying to get it so that if noFlag is null, it enters a null in the database, but I'm getting errors:

Cannot implicitly convert type 'string' to 'bool'

and

Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DBNull' and 'string'

Answer 1

Sayka was on target. Use parameters .

Not only will you protect your database from sql injection attacks but you can take advantage of .Nets built in functionality to handle these types of issues.

    CommandText = @"UPDATE thetable SET Yes = @yesFlag, NoFlag = @noflag, NextValue = 10";
    Command.Parameters.AddWithValue("@yesFlag", list.yesFlag);
    Command.Parameters.AddWithValue("@noFlag", list.previous);

Answer 2

Using parameters is strongly recommended. But in your case you just enter as 'Null'. It will work.

CommandText = @"UPDATE thetable SET Yes = " + 
             list.yesFlag.ToString() + ",NoFlag = " + (list.previous == null 
             ? "NULL" : list.previous) + ",NextValue = 10";

This query will go as it is.