How to use unsigned int / long types with Entity Framework?

Update Entity Framework Core Feb 2021

EF Core 3.1: EF Core now supports long and ulong types. Using code first, the long or ulong is mapped to EF Core's new 'Decimal Type'

public ulong MyULong{ get; set; } //==> decimal(20, 0)

A ulong results in a decimal being defined in the database with 20 digits and 0 digits to the right of the decimal point, which is sufficient to store a 64 bit ulong.

EF 5: Thankyou to @Tomasz for noting that in EF 5 and 6 the ulong is mapped to a BigInt, rather than the Decimal type as per my original answer, now under the heading "EF Core 3.1" above

Update Feb 2021

Apparently EF Core now supports ulong -- see @JimbobTheSailor's answer below.

---

Older Entity Framework versions:

Turns out that Entity Framework does not support unsigned data types. For uint columns, one could just store the value in a signed data type with a larger range (that is, a long). What about ulong columns? The common solution couldn't work for me because there is no EF-supported signed data type that can hold a ulong without overflowing.

After a bit of thinking, I figured out a simple solution to this problem: just store the data in the supported long type and cast it to ulong when accessed. You might be thinking: "But wait, ulong's max value > long's max value!" You can still store the bytes of a ulong in a long and then cast it back to ulong when you need it, since both have 8 bytes. This will allow you to save a ulong variable to a database through EF.

// Avoid modifying the following directly.
// Used as a database column only.
public long __MyVariable { get; set; }

// Access/modify this variable instead.
// Tell EF not to map this field to a Db table
[NotMapped]
public ulong MyVariable
{
    get
    {
        unchecked
        {
            return (ulong)__MyVariable;
        }
    }

    set
    {
        unchecked
        {
            __MyVariable = (long)value;
        }
    }
}

The casting is unchecked to prevent overflow exceptions.

Hope this helps someone.