How to set null to a GUID property

问题

I have an object of type Employee which has a Guid property. I know if I want to set to null I must to define my type property as nullable Nullable<Guid> prop or Guid? prop.

But in my case I'm not able to change the type of the prop, so it will remains as Guid type and my colleague and I we don't want to use the Guid.Empty.

Is there a way to set my property as null or string.empty in order to restablish the field in the database as null.

I have a mechanism to transform from string.empty to null but I will change many things if the would change to accept a empty guid to null.

Any help please!

回答1:

Is there a way to set my property as null or string.empty in order to restablish the field in the database as null.

No. Because it's non-nullable. If you want it to be nullable, you have to use Nullable<Guid> - if you didn't, there'd be no point in having Nullable<T> to start with. You've got a fundamental issue here - which you actually know, given your first paragraph. You've said, "I know if I want to achieve A, I must do B - but I want to achieve A without doing B." That's impossible by definition.

The closest you can get is to use one specific GUID to stand in for a null value - Guid.Empty (also available as default(Guid) where appropriate, e.g. for the default value of an optional parameter) being the obvious candidate, but one you've rejected for unspecified reasons.

回答2:

Guid? myGuidVar = (Guid?)null;

It could be. Unnecessary casting not required.

Guid? myGuidVar = null;

回答3:

Since "Guid" is not nullable, use "Guid.Empty" as default value.

回答4:

Choose your poison - if you can't change the type of the property to be nullable then you're going to have to use a "magic" value to represent NULL. Guid.Empty seems as good as any unless you have some specific reason for not wanting to use it. A second choice would be Guid.Parse("ffffffff-ffff-ffff-ffff-ffffffffffff") but that's a lot uglier IMHO.

回答5:

You can use typeof(Guid), "00000000-0000-0000-0000-000000000000" for DefaultValue of the property.

回答6:

you can make guid variable to accept null first using ? operator then you use Guid.Empty or typecast it to null using (Guid?)null;

eg:

 Guid? id = Guid.Empty;

 Guid? id =  (Guid?)null;

回答7:

extrac Guid values from database functions:

    #region GUID

    public static Guid GGuid(SqlDataReader reader, string field)
    {
        try
        {
            return reader[field] == DBNull.Value ? Guid.Empty : (Guid)reader[field];
        }
        catch { return Guid.Empty; }
    }

    public static Guid GGuid(SqlDataReader reader, int ordinal = 0)
    {
        try
        {
            return reader[ordinal] == DBNull.Value ? Guid.Empty : (Guid)reader[ordinal];
        }
        catch { return Guid.Empty; }
    }

    public static Guid? NGuid(SqlDataReader reader, string field)
    {
        try
        {
            if (reader[field] == DBNull.Value) return (Guid?)null; else return (Guid)reader[field];
        }
        catch { return (Guid?)null; }
    }

    public static Guid? NGuid(SqlDataReader reader, int ordinal = 0)
    {
        try
        {
            if (reader[ordinal] == DBNull.Value) return (Guid?)null; else return (Guid)reader[ordinal];
        }
        catch { return (Guid?)null; }
    }

    #endregion

回答8:

I think this is the correct way:

Guid filed = Guid.Empty;

来源：https://stackoverflow.com/questions/20501104/how-to-set-null-to-a-guid-property

标签

guid

nullable