Model First Development using POCOs in Entity Framework

Entity framework supports the concept of model first development and then generating a database based on the model created. Along with the model created the entity framework generates the classes for the model entities which are heavily dependent on the plumbing of the framework. These auto generated classes know too much information about the persistence mechanism and are tied closely to the concerns of models and mappings. For a developer who wants to create a commonly accepted and easily understandable framework of objects, these classes are not very helpful. In this post I’ll explain how to create a customer – order scenario with model first development and POCO support.

1.       In your model project add a new ADO.NET entity data model and select ‘Empty model’ from the options and click finish. I have named my model ‘ShoppingCartModel.edmx’.

2.       In my model I have created the entities like given in the figure below.

3.       Every entity has a Timestamp field which is used to manage concurrency. To generate Timestamp fields in the DB you can follow the steps mentioned in this post.

4.       Right click the model and select Properties. Set the code generation strategy to ‘None’. This will prevent the auto generation of the classes from the model. 

5.       Right click the model and select ‘Generate Database from model’. Complete the connection string specifications and click Finish. This will generate the .SQL file with the DB scripts and save in the current project. You can use this script to generate the DB and the tables.

6.       Next we’ll create our POCO classes for the entity model. 

public class BaseEntity

{

    public Guid Id { get; set; }

    public DateTime CreatedDate { get; set; }

    public DateTime ChangedDate { get; set; }

    public byte[] Timestamp { get; set; }

}

public class Customer : BaseEntity

{

    public Customer()

    {

        Orders = new HashSet<Order>();

    }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public virtual ICollection<Order> Orders { get; set; }

}

public class Order : BaseEntity

{

    public Order()

    {

        OrderProducts = new HashSet<OrderProduct>();

    }

    public DateTime OrderDate { get; set; }

    public string OrderNumber { get; set; }

    public Guid CustomerId {get; set; }

    public Customer Customer { get; set; }

    public virtual ICollection<OrderProduct> OrderProducts { get; set; }

}

public class Product : BaseEntity

{

    public string ProductName { get; set; }

    public decimal UnitPrice { get; set; }

    public ICollection<OrderProduct> OrderProducts { get; set; }

}

public class OrderProduct

{

    public Guid OrderId { get; set; }

    public Guid ProductId { get; set; }

    public Order Order { get; set; }

    public Product Product { get; set; }

    public int Quantity { get; set; }

    public decimal TotalPrice { get; set; }

}

7.       Next we need to create the ObjectContext implementation.

public class ShoppingCartContext : ObjectContext

{

    public ShoppingCartContext() : base("name=ShoppingCartModelContainer", "ShoppingCartModelContainer") { }

    public ObjectSet<Customer> Customers

    {

        get { return _customers ?? CreateObjectSet<Customer>(); }

    }

    public ObjectSet<Order> Orders

    {

        get { return _orders ?? CreateObjectSet<Order>(); }

    }

    public ObjectSet<Product> Products

    {

        get { return _products ?? CreateObjectSet<Product>(); }

    }      

    ObjectSet<Customer> _customers;

    ObjectSet<Order> _orders;

    ObjectSet<Product> _products;

}

You can use this context to perform CRUD operations on the model like.

[TestMethod()]

public void lazy_loading_should_be_able_to_retrieve_data_from_the_db()

{

    var customer = SetupCustomerWithOrderAndProduct();

    using (var context = new ShoppingCartContext())

    {

        context.ContextOptions.LazyLoadingEnabled = true;

        var customerFromDb = (from c in context.Customers

                        where c.Id == customer.Id

                        select c).FirstOrDefault();

        var order = (from o in customerFromDb.Orders

                        where o.OrderNumber.Contains("ORD")

                        select o).FirstOrDefault();

        Assert.IsTrue(order.OrderProducts.Count == 1);

    }

}

This approach can be used to create a repository and unit of work pattern efficiently.