Tip 42 – How to create a dynamic model using Code-Only


When we give examples of how to use Code-Only we always start with a strongly typed Context derived from ObjectContext. This class is used to bootstrap the model.

For example this (property bodies omitted for simplicity sake):

public class MyContext : ObjectContext

   public ObjectSet<Category> Categories { get; }
   public ObjectSet<Product> Products { get; }

Tells CodeOnly that to bootstrap a model with 2 EntitySets, a set of Category entities called Categories, and a set of Product entities called Products.

Then if necessary you can further refine the model by manipulating the ContextBuilder.


But what if you don’t have a strongly typed Context class?

What if you make a determination at runtime that you need a model, there isn’t an appropriate strongly typed Context class lying around.

A customer asked me this very question earlier today.


It turns out you can use ObjectContext directly. When you do this though Code-Only knows nothing about the model. But that isn’t that bad all you need to do is explicitly tell Code-Only about all the things it would normally learn from the strongly typed context.

For example this:

public ObjectSet<Person> People { get; }

Can be converted into this:

var builder = new ContextBuilder<ObjectContext>();

Nifty huh?

End to end example:

This example, persists a Person (BillG) to the database and retrieves it again, all without a strongly typed ObjectContext:

First the Person class (which is POCO):

public class Person
    public int ID { get; set; }
    public string Firstname { get; set; }
    public string Surname { get; set; }

And now the code to setup the ObjectContext:

// Create the contextbuilder, and tell it about the People set.
var builder = new ContextBuilder<ObjectContext>();

// Create a connection
string connstr = @”Data Source=.\SQLEXPRESS;Initial Catalog=PeopleDb;Integrated Security=True;Pooling=False;MultipleActiveResultSets=True”;
var conn = new SqlConnection(connstr);

// Create an ObjectContext from the builder
using (ObjectContext ctx = builder.Create(conn))
    // Create the database if it doesn’t already exist
    if (!ctx.DatabaseExists())

    // Create Bill
    Person p = new Person {
        ID = 1,
        Firstname = “Bill”,
        Surname = “Gates”

    // Add Bill to the context
    // UPDATE: thanks to danny for the simplification
 using the general purpose
    // AddObject method.
    // The only tricky part is the EntitySet name with must 
    // be qualified with the the container name,  
    // in this case is ObjectContext.
    ctx.AddObject(“ObjectContext.People”, p);


    // Issue a query against the People set.
    var bill = (from person in ctx.CreateObjectSet<Person>()
                where person.Firstname == “Bill”
                select person).Single();

    // Make and Save a change.
    bill.Firstname = “William”;

Pretty easy considering it isn’t strongly typed.

Comments (5)

  1. Hi!

    How about an RegisterSet that takes a Type instead of a generic version? Then You could register this dynamically.

    I have put up an similar example that could be found:



  2. By the way, if you won’t want to figure out the entity set name, you could just change the AddObject line you have above to:


    • Danny
  3. Just curious, why most of you code snippet uses ObjectSet instead of IObjectSet, the same is true for IList<T> and List<T>. I did a blog post on this issue which you find interesting: http://weblogs.asp.net/rashid/archive/2009/09/13/shrinkr-url-shrinking-service-developed-with-entity-framework-4-0-unity-asp-net-mvc-and-jquery-part-2.aspx

  4. AlexJ says:


    No real reason, you could obviously do this with IObjectSet and IList etc.

    But for this post I wasn’t focusing on testability.

    Thanks for the link.


  5. Hi!

    I have now updated my EfEntityStore so that it lets you Auto-register entitymappings and registers the Entitysets etc. You can check it out at: http://daniel.wertheim.se/2009/11/13/entity-framework-4-part-4-autoregister-entitymappings/