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How to: Define a Custom Object Context

.NET Framework 4

When you use POCO entities, you disable object layer generation by the Entity Framework. In addition to defining custom entity types, you need to either define a custom object context type or manage your own connections through a manually created instance of EntityConnection that you pass to the constructor of the ObjectContext. For information about how to create an EntityConnection, see How to: Build an EntityConnection Connection String.

This topic demonstrates how to create a custom object context.

Note:
To disable object layer generation with the ADO.NET Entity Data Model Designer (Entity Designer), open the .edmx file in the Entity Designer. Right-click on the designer surface and select Properties. In the Properties window, select the Code Generation Strategy property and select None.

The custom object context class manages the POCO entities that are defined in How to: Define POCO Entities.

A custom object context should include the following functionality:

The ability to instantiate an ObjectContext that is specific to your conceptual model, including predefined connections.
Properties that return type-specific ObjectSet objects.

For information about defining custom entity types, see How to: Define POCO Entities.

To use generated object context code in your custom object context code

Add a class code file to your project.
Include the following namespaces:

System

System.Data.Objects

System.Collections.Generic
Rename the class to POCOAdventureWorksEntities. Make sure the class inherits from the ObjectContext class.
C#
VB
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public partial class POCOAdventureWorksEntities : ObjectContext

Define member variables of the ObjectSet type for each POCO entity type:

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private ObjectSet<Contact> _contacts;
private ObjectSet<LineItem> _lineItems;
private ObjectSet<Order> _orders;

Define constructors to the POCOAdventureWorksEntities class.

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 public POCOAdventureWorksEntities()
     : base("name=AdventureWorksEntities", "AdventureWorksEntities")
 {
     this.ContextOptions.LazyLoadingEnabled = true;
}

 public POCOAdventureWorksEntities(string connectionString)
     : base(connectionString, "AdventureWorksEntities")
 {
     this.ContextOptions.LazyLoadingEnabled = true;
 }

Define properties that return ObjectSet objects.

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public ObjectSet<Contact> Contacts
{
    get
    {
        return _contacts ?? (_contacts = base.CreateObjectSet<Contact>());
    }
}

public ObjectSet<LineItem> LineItems
{
    get
    {
        return _lineItems ?? (_lineItems = base.CreateObjectSet<LineItem>());
    }
}

public ObjectSet<Order> Orders
{
    get
    {
        return _orders ?? (_orders = base.CreateObjectSet<Order>());
    }
}

Example

This example shows the custom object context code that supports the Contact, Order, and LineItem custom data classes.

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public partial class POCOAdventureWorksEntities : ObjectContext
{
    private ObjectSet<Contact> _contacts;
    private ObjectSet<LineItem> _lineItems;
    private ObjectSet<Order> _orders;
    #region Constructors
    public POCOAdventureWorksEntities()
        : base("name=AdventureWorksEntities", "AdventureWorksEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
   }

    public POCOAdventureWorksEntities(string connectionString)
        : base(connectionString, "AdventureWorksEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
    }
    #endregion

    #region ObjectSet Properties
    public ObjectSet<Contact> Contacts
    {
        get
        {
            return _contacts ?? (_contacts = base.CreateObjectSet<Contact>());
        }
    }

    public ObjectSet<LineItem> LineItems
    {
        get
        {
            return _lineItems ?? (_lineItems = base.CreateObjectSet<LineItem>());
        }
    }

    public ObjectSet<Order> Orders
    {
        get
        {
            return _orders ?? (_orders = base.CreateObjectSet<Order>());
        }
    }

    #endregion
    public override int SaveChanges(SaveOptions options)
    {

        foreach (ObjectStateEntry entry in
            ObjectStateManager.GetObjectStateEntries(
            EntityState.Added | EntityState.Modified))
        {
            // Validate the objects in the Added and Modified state
            // if the validation fails throw an exeption.
        }
        return base.SaveChanges(options);
    }

}

How to: Define a Custom Object Context

To use generated object context code in your custom object context code

Example

See Also

Reference

Concepts

Other Resources