如何在C＃中将System.Data.Linq.Binary分配为null？

Question

I have an SQL Server table with a column NameHash with type binary(16) which allows nulls.

In my C# application, I have a very basic MD5 hashing extension method:

public static byte[] CalculateMD5HashBinary(this string input)
{
    if (String.IsNullOrEmpty(input))
    {
        return null;
    }

    MD5 md5 = System.Security.Cryptography.MD5.Create();
    byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);

    return md5.ComputeHash(inputBytes);
}

I am using LINQ to SQL to assign the value:

var fooBar = MyContext.FooBars.First();
fooBar.NameHash = fooBar.Name.CalculateMD5HashBinary();
MyContext.SubmitChanges();

When Name is null or empty, the NameHash column should be null. However, when I save this value in the DB, I check the values I see the hex string 0x00000000000000000000000000000000 instead.

Why does it do this? How can I get a null value properly assigned into the NameHash binary column?

Answer 1

I figured this out after some messing around.

LINQ-to-SQL takes the Binary(16) SQL-Server type and makes it of type System.Data.Linq.Binary in C#.

You can assign Byte[] values to Binary variables and do boolean comparisons the two, so I was using them some-what interchangeably.

What I realized is that my extension method of return type Byte[] was setting {""} to the NameHash value instead of null for whatever reason. I changed the return type to Binary and it solved my problem.

using System.Data.Linq;

public static Binary CalculateMD5HashBinary(this string input)
{
    if (String.IsNullOrEmpty(input))
    {
        return null;
    }

    MD5 md5 = System.Security.Cryptography.MD5.Create();
    byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);

    return md5.ComputeHash(inputBytes);
}