Autogenerated Guid Id is empty when updated via Entity Framework - entity-framework

Question

To try to isolate the source of a bug I have built the following:
SQL Server table:
CREATE TABLE [dbo].[Names]
([Key] [uniqueidentifier] NOT NULL,
[Name] [nvarchar](50) NULL,
CONSTRAINT [PK_Names] PRIMARY KEY CLUSTERED ([Key] ASC)
)
GO
ALTER TABLE [dbo].[Names] ADD CONSTRAINT [DF_Names_Key] DEFAULT (newid()) FOR [Key]
When I add rows to this table via the SQL Server Management Studio the guid gets a value as expected.
I then create an EF model with this table, this generated the following code:
/// <summary>
/// No Metadata Documentation available.
/// </summary>
[EdmEntityTypeAttribute(NamespaceName="Model1", Name="Names")]
[Serializable()]
[DataContractAttribute(IsReference=true)]
public partial class Names : EntityObject
{
#region Factory Method
/// <summary>
/// Create a new Names object.
/// </summary>
/// <param name="key">Initial value of the Key property.</param>
public static Names CreateNames(global::System.Guid key)
{
Names names = new Names();
names.Key = key;
return names;
}
#endregion
#region Primitive Properties
/// <summary>
/// No Metadata Documentation available.
/// </summary>
[EdmScalarPropertyAttribute(EntityKeyProperty=true, IsNullable=false)]
[DataMemberAttribute()]
public global::System.Guid Key
{
get
{
return _Key;
}
set
{
if (_Key != value)
{
OnKeyChanging(value);
ReportPropertyChanging("Key");
_Key = StructuralObject.SetValidValue(value);
ReportPropertyChanged("Key");
OnKeyChanged();
}
}
}
private global::System.Guid _Key;
partial void OnKeyChanging(global::System.Guid value);
partial void OnKeyChanged();
/// <summary>
/// No Metadata Documentation available.
/// </summary>
[EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=true)]
[DataMemberAttribute()]
public global::System.String Name
{
get
{
return _Name;
}
set
{
OnNameChanging(value);
ReportPropertyChanging("Name");
_Name = StructuralObject.SetValidValue(value, true);
ReportPropertyChanged("Name");
OnNameChanged();
}
}
private global::System.String _Name;
partial void OnNameChanging(global::System.String value);
partial void OnNameChanged();
I then created a test to add data to the table:
[TestMethod]
public void WriteTestMethod1()
{
using (Model1Container context = new Model1Container())
{
Names n = new Names();
n.Name = "T2";
context.Names.AddObject(n);
context.SaveChanges();
}
}
The result of this is that the row is inserted but the Guid is Empty (all zeros)
Why is this happening? Can EF work with database generated Guids?

Answer 1

This is old, but here is an answer anyway, since it's still relevant.
Your test code creates an instance of class Names and assigns a value to the Name property.
You don't explicitly assign anything to the Key property. The Key property is of type Guid, which is a struct (value type), not a class (reference type), so it can never be null and will always have a value, if just the default. The uninitialized default value of a Guid is all zero fields.
When you add/persist this entity instance, EF generates an INSERT to both fields, since values exist for both.
The default value expression defined in your schema is not used because a value was provided in the INSERT statement from the client side.
You can get a server generated uid value by defining the Key field as nullable, which will correspond with field type in C# of Guid? (rather than Guid). Then you can allow the Key value to remain null in your code and the server defined default expression will be used.
However, if this field is your primary key, a nullable field may not be what you need. When I'm in this situation I use a constructor that sets a Guid value (yes, on the client side) rather than allowing it to take the default value.