Hello,

here is a short but complete example of adding and removing fields dynamically.

There are no limitations for DB however if you're going to change your model you'll need to perform a regular upgrade over the database.

Unfortunately due to techinal limitations dynamic fields are not fully usable in LINQ unless there is a real property defined for the field in question.

using System;
using System.Linq;
using Xtensive.Orm;
using Xtensive.Orm.Building;
using Xtensive.Orm.Building.Definitions;
using Xtensive.Orm.Configuration;

namespace DynamicEntitySample
{
  [HierarchyRoot]
  public class DynamicEntity : Entity
  {
    [Key, Field]
    public long Id { get; private set; }

    [Field]
    public string FieldToRemove { get; set; }

    public DynamicEntity(Session session)
      : base(session)
    {
    }
  }

  public class MyModule : Module
  {
    public override void OnDefinitionsBuilt(BuildingContext context, DomainModelDef model)
    {
      // Removing existing field
      var dynamicEntityType = model.Types[typeof (DynamicEntity)];
      var fieldToRemove = dynamicEntityType.Fields["FieldToRemove"];
      dynamicEntityType.Fields.Remove(fieldToRemove);
      // Adding new field
      dynamicEntityType.DefineField("FieldToAdd", typeof (string));
    }
  }

  internal static class Program
  {
    private static void Main(string[] args)
    {
      var configuration = new DomainConfiguration("sqlserver",
        "Data Source=localhost;Initial Catalog=DO-Tests;Integrated Security=True;MultipleActiveResultSets=True");
      configuration.UpgradeMode = DomainUpgradeMode.Recreate;
      configuration.Types.Register(typeof (DynamicEntity).Assembly);
      var domain = Domain.Build(configuration);

      using (var session = domain.OpenSession())
      using (var tx = session.OpenTransaction()) {
        var entity = new DynamicEntity(session);
        // Setting dynamic field value
        entity["FieldToAdd"] = "Hello dynamic world!";
        tx.Complete();
      }

      using (var session = domain.OpenSession())
      using (var tx = session.OpenTransaction()) {
        var entity = session.Query.All<DynamicEntity>().Single();
        // Reading dynamic field value
        Console.WriteLine(entity["FieldToAdd"]);
        tx.Complete();
      }
    }
  }
}