ObjectContext

• **ObjectContext** is responsible for:
  • Database connection.
  • Builtin Add, Update and Delete functions.
  • Object Set of every entity.
  • Provide State of pending changes.
  • It holds the changes done in entities.
• **ObjectContext** also encapsulates these:
  • Connection to the Data Store or Database.
  • Metadata in the Entity Data Model (EDM).
  • ObjectStateManager to track changes to the objects.
• **ObjectContext** supports Compiled Queries and self-tracking of Entities.

public class MyObjectContext : ObjectContext
{
	// It uses "ObjectSet" instead of "DbSet":
	public ObjectSet<Clan> Clans { get; set; }
	public ObjectSet<NinjaEquipment> NinjaEquipments { get; set; }
	public ObjectSet<Ninja> Ninjas { get; set; }

	public MyObjectContext() : base("name=MyObjectContext")
	{
		Clans = CreateObjectSet<Clan>();
		NinjaEquipments = CreateObjectSet<NinjaEquipment>();
		Ninjas = CreateObjectSet<Ninja>();
	}

	// It doesn't use "OnModelCreating".
}

DbContext

• DbContext is the primary class that is responsible for interacting with data as object.

• DBContext represents a combination of the Unit-Of-Work and Repository patterns. It does following activities:

  1. Querying: It can be useful in querying the database. It converts database values into entity objects and vice versa.
  2. Change Tracking: It keeps track of changes occurred in the entities after it has been querying from the database.
  3. Persisting Data: It also performs the Insert, update and delete operations to the database, based on the entity states.

• DbContext is conceptually similar to **ObjectContext**.

  • It is a wrapper around ObjectContext.

• DBContext API is easier to use than ObjectContext API for all common tasks.

  • However, you can get the reference of ObjectContext from DBContext in order to use some of the features of ObjectContext.
  • This can be done by using IObjectContextAdapter:

  using (var db = new MyDbContext())
  {
  	var objectContext = (context as IObjectContextAdapter).ObjectContext;
  	ObjectQuery<Ninja> ninjas = objectContext.CreateQuery<Ninja>(
  		@"SELECT VALUE n FROM NinjaContext.Ninjas AS n WHERE n.DateOfBirth > @dob", 
  		new ObjectParameter[] { new ObjectParameter("dob", new DateTime(1984, 1, 1)) });
  }
  

• **DbContext** is not thread-safe.

  • This might result on multiple queries being sent concurrently over the same database connection.
  • It will also corrupt the first-level cache that **DbContext** maintains to offer its Identity Map, change tracking and Unit of Work functionalities.
  • You must never access your **DbContext**-derived instance from multiple threads simultaneously.
  • In a multi-threaded application, you must create and use a separate instance of your **DbContext** in each thread.

DBSet

• DBSet class represents an entity set that is used for the create, read, update, and delete operations.
• A generic version of DBSet (DbSet<TEntity>) can be used when the type of entity is not known at build time.

DBEntityEntry

• It is useful in retrieving various information about an entity.
• You can get an instance of it for a particular entity by using **Entry** method of DBContext:

`**DBEntityEntry studentEntry = dbcontext.Entry(StudentEntity);**`

DbContext Lifetime

• Options often cited include one per: Function, Form, Thread, and Application.