Creating a generic database context in MVC 4 - entity-framework

Question

I wrote a MVC 4 app. I have some questions:
public class DatabaseContext<TEntity>: DbContext where TEntity: class
{
...
public DbSet<TEntity> entity = {get; set;}
...
}
I want to create a generic database context like this DatabaseContext and use it for all my Entities defined in database tables.
Please, write an example.
I don't now how to initialize generic context in global.asax once and use it every time, in whichever part of the project necessary.
Please, write some examples.

Answer 1

It seems to me to what you're implementing is the Repository Pattern:
public interface IRepository<TEntity> where TEntity : class
{
IEnumerable<TEntity> GetAll();
TEntity GetById(Guid id);
}
Prevent letting your repository inherit from DbContext, since DbContext is an implementation of the Unit of Work pattern and a unit of work is not a repository (but rather contains or manages multiple repositories).
What you can do is to let your repository use the DbContext internally:
public class Repository<TEntity> : IRepository<TEntity>
{
private readonly DbContext context;
public Repository(DbContext context)
{
this.context = context;
}
public IEnumerable<TEntity> GetAll()
{
return this.context.Set<TEntity>();
}
public TEntity GetById(Guid id)
{
var entity = this.context.Set<Entity>().Find(id);
if (entity == null) throw new KeyNotFoundException(
typeof(TEntity).Name + " with id " + id + " not found);
return entity;
}
}
UPDATE
Since I'm a Dependency Injection enthusiast, I think that Dependency Injection is the solution to your problem. And since I'm a developer for the Simple Injector project, I'll show you how to do this using Simple Injector:
Step 1: Install the Simple Injector MVC Integration Quick Start NuGet package into your MVC project (I assume you know how to install NuGet packages).
Step 2: Compile your project. You'll get a compiler error in the SimpleInjectorInitializer class that the package just added. This is the line where you will have to make your registrations. You can just remove this #error line.
Step 3: Add the SimpleInjector.Extensions namespace to the top of the SimpleInjectorInitializer file:
using SimpleInjector.Extensions;
Step 4: Make the following registrations in the InitializeContainer method:
container.RegisterOpenGeneric(typeof(IRepository<>), typeof(Repository<>));
container.RegisterPerWebRequest<DbContext>(
() => new DbContext("Your connection string here"));
Step 5: Add the IRepository<T> dependencies to your contollers:
public class CustomerController : Controller
{
private readonly IRepository<Customer> customerRepository;
public CustomerController(IRepository<Customer> customerRepository)
{
this.customerRepository = customerRepository;
}
// controller methods here.
}
Now your repositories will be automatically be injected into your controllers.

Answer 2

Is there a reason you want to make a DatabaseContext with a generic type parameter? You won't be to instantiate it in a single place because each different DatabaseContext is a separate .NET Type.
Unless you're sticking rigidly to a particular pattern, I personally don't see any practical advantage of this approach over a single DatabaseContext with many sets:
public class DatabaseContext: DbContext
{
public DbSet<SomeEntity> SomeEntities { get; set; }
public DbSet<OtherEntity> OtherEntities { get; set; }
}
...
myDatabaseContext.SomeEntities.GetAll();
myDatabaseContext.OtherEntities.GetAll();
// OR:
myDatabaseContext.Set<SomeEntity>().GetAll();
myDatabaseContext.Set<OtherEntity>().GetAll();