In this article we will be discussing how we can create a Generic Data Access Layer which we could use in developing our Business Applications.

Lets start by creating a Data Model.

Create a ADO.NET Entity Data Model as shown below :

GDAccLyr1.gif

Once the Data Model is added to my project, I can then move to the next step, Creating a Repository.

Creating a Repository Class

public class Repository<T> where T : EntityObject
 {
IObjectSet<T> _objectSet;

/// <summary>
 /// This method is used to pass the Context object as a parameter to the Respository
 /// </summary>
 /// <param name="objectContext"></param>
 public Repository(ObjectContext objectContext)
{
_objectSet = objectContext.CreateObjectSet<T>();
}

/// <summary>
 /// This method we manually pass the Context Object
 ///
/// </summary>
 public Repository()
{
DataEntities context = new DataEntities ();
_objectSet = context.CreateObjectSet<T>();
}

public IQueryable<T> AsQueryable()
{
return _objectSet;
}

public IEnumerable<T> GetAll()
{
return _objectSet.ToList();
}

public IEnumerable<T> Find(Expression<Func<T, bool>> where)
{
return _objectSet.Where(where);
}

public T Single(Expression<Func<T, bool>> where)
{
return _objectSet.Single(where);
}

public T First(Expression<Func<T, bool>> where)
{
return _objectSet.First(where);
}

public void Delete(T entity)
{
_objectSet.DeleteObject(entity);
}

public void Add(T entity)
{
_objectSet.AddObject(entity);
}

public void Attach(T entity)
{
_objectSet.Attach(entity);
}
}

I can now use this Repository Class in a Client Project and easily access or modify the Entities using the Above methods.

The client code would look like below :

 Repository<Company> company = new Repository<Company>();

foreach (Company comp in company.GetAll())
{
Console.WriteLine(comp.Name);
}
Console.ReadLine();

Note that here I am not using the context object at all to get the entities as I have already taken care of that in the below code in Repository Class .

 /// <summary>
/// This method we manually pass the Context Object
///
/// </summary>
public Repository()
{
DataEntities context = new DataEntities ();
_objectSet = context.CreateObjectSet<T>();
}

Thanks . In my next post we will look into how we can improve on this Data access Layer which we have just created.