Entity Framework auto incrementing field, that isn't the Id - entity-framework

Question

I know this isn't the most ideal solution, but I need to add an auto incrementing field to one of my EF Code First objects. This column id NOT the Id, which is a guid.
Is there anyway for me to define the auto incrementing field in code, or would creating the column myself and defining in the DB that its auto incrementing work?

Answer 1

You can annotate that property with DatabaseGenerated(DatabaseGeneratedOption.Identity). EF allows only single identity column per table.
public class Foo
{
[Key]
public Guid Id { get; set; }
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public long Bar { get; set; }
}

Answer 2

Old post thought I would share what I found with Entity Framework 6.1.3.
I created a simple data layer library using C# and .NET Framework 4.6.1, added a simple repository/service class, a code first context class and pointed my web.config file to a local SQL Express 2014 database.
In the entity class I added the following attribute constructor to the Id column:
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id { get; set; }
Then I created a new migration by typing the following in Visual Studio 2015 Package Manager:
Add-Migration
Give the migration a name and then wait for the DbMigtation class to be created. Edit the class and add the following CreateTable operation:
CreateTable(
"dbo.Article",
c => new
{
Id = c.Guid(nullable: false, identity: true),
Title = c.String(),
Content = c.String(),
PublishedDate = c.DateTime(nullable: false),
Author = c.String(),
CreateDate = c.DateTime(nullable: false),
})
.PrimaryKey(t => t.Id);
}
The above table is an example the key point here is the following builder annotation:
nullable: false, identity: true
This tells EF to specifiy the column as not nullabe and you want to set it as an identity column to be seeded by EF.
Run the migration again with the following command:
update-database
This will run the migration class dropping the table first (Down() method) then creating the table (Up() method).
Run your unit tests and/or connect to the database and run a select query you should see your table in its new form, add some data excluding the Id column and you should see new Guid's (or whatever data type your choose) to be generated.

Answer 3

For those stumbling onto this question for EF Core, you can now create an auto-incrementing column with your model builder as follows:
builder.Entity<YourEntity>().Property(e => e.YourAutoIncrementProperty).UseNpgsqlIdentityAlwaysColumn();
Reference: https://www.npgsql.org/efcore/modeling/generated-properties.html