GUID COMB strategy in EF
c#, entity-framework, entity-framework-migrations, guid, newsequentialid
Solution
I guess you are using SQL server as your database. This is nice example of inconsistency among different MS tools. SQL server team doesn't recommend using `newid()` as default value for `UNIQUEIDENTIFIER` columns and ADO.NET team use it if you specify `Guid` property as autogenerated in the database. They should use `newsequentialid()` instead!
If you want sequential Guids generated by database you must modify generated table and it is really complex because you must find autogenerated default constraint, drop it and create new constraint. This all can be done in custom database initializer. Here you have my sample code:
class Program
{
static void Main(string[] args)
{
Database.SetInitializer(new CustomInitializer());
using (var context = new Context())
{
context.TestEntities.Add(new TestEntity() { Name = "A" });
context.TestEntities.Add(new TestEntity() { Name = "B" });
context.SaveChanges();
}
}
}
public class CustomInitializer : DropCreateDatabaseAlways<Context>
{
protected override void Seed(Context context)
{
base.Seed(context);
context.Database.ExecuteSqlCommand(@"
DECLARE @Name VARCHAR(100)
SELECT @Name = O.Name FROM sys.objects AS O
INNER JOIN sys.tables AS T ON O.parent_object_id = T.object_id
WHERE O.type_desc LIKE 'DEFAULT_CONSTRAINT'
AND O.Name LIKE 'DF__TestEntities__Id__%'
AND T.Name = 'TestEntities'
DECLARE @Sql NVARCHAR(2000) = 'ALTER TABLE TestEntities DROP Constraint ' + @Name
EXEC sp_executesql @Sql
ALTER TABLE TestEntities
ADD CONSTRAINT IdDef DEFAULT NEWSEQUENTIALID() FOR Id");
}
}
public class TestEntity
{
public Guid Id { get; set; }
public string Name { get; set; }
}
public class Context : DbContext
{
public DbSet<TestEntity> TestEntities { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<TestEntity>()
.Property(e => e.Id)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
}
}
Problem
Is there any way to implement the Guid COMB identity strategy for objects in the new Entity Framework 4.1 using the CodeFirst design? I thought setting the `StoreGeneratedPattern` would work, but it still gives me normal GUIDs.