Introduction
Creating a Generic Repository pattern in an MVC3 application with Entity
Framework is the last topic that we are about to cover in our journey
of learning MVC.
The article will focus on Unit of Work Pattern and Repository Pattern,
and shows how to perform CRUD operations in an MVC application when
there could be a possibility of creating more than one repository class.
To overcome this possibility and overhead, we make a Generic Repository
class for all other repositories and implement a Unit of Work pattern
to provide abstraction.
Our roadmap towards Learning MVC
Just to remind our full roadmap towards learning MVC,
- Part1: Introduction to MVCarchitecture and Separation of Concerns.
- Part 2: Creating MVC Application fromscratch and connecting it with database using LINQ to SQL.
- Part 3: Connecting the MVC Application with the help of EntityFramework DB-First approach.
- Part 4: Connecting the MVC Application with the help of EntityFramework Code-First approach.
- Part 5: Implementing Repository Pattern in MVC Application with EntityFramework.
- Part 6: Implementing a generic Repository Pattern and Unit Of Work pattern in MVC Application with EntityFramework.
Pre-requisites
There are few pre-requisites before we start with the article,
- We have running sample application that we created in fifth part of the article series.
- We have Entity Framework 4.1 package or DLL on our local file system.
- We understand how MVC application is created (follow second part of the series).
Why Generic Repository
We have already discussed what Repository Pattern is and why do we need Repository Pattern in our last article.
We created a User Repository for performing CRUD operations, but think
of the scenario where we need 10 such repositories.
Are we going to create these classes? Not good, it results in a lot of
redundant code. So to overcome this situation we’ll create a Generic
Repository class that will be called by a property to create a new
repository thus we do not result in lot of classes and also escape
redundant code too. Moreover we save a lot of time that could be wasted
creating those classes.
Unit of Work Pattern
According to Martin Fowler Unit of Work Pattern “Maintains a list of
objects affected by a business transaction and coordinates the writing
out of changes and the resolution of concurrency problems."
From MSDN, The Unit of Work pattern isn't necessarily something that you
will explicitly build yourself, but the pattern shows up in almost
every persistence tool. The
ITransaction interface in NHibernate, the DataContextclass in LINQ to SQL, and the ObjectContext class
in the Entity Framework are all examples of a Unit of Work. For that
matter, the venerable DataSet can be used as a Unit of Work.
Other times, you may want to write your own application-specific Unit of
Work interface or class that wraps the inner Unit of Work from your
persistence tool. You may do this for a number of reasons. You might
want to add application-specific logging, tracing, or error handling to
transaction management. Perhaps you want to encapsulate the specifics of
your persistence tooling from the rest of the application. You might
want this extra encapsulation to make it easier to swap out persistence
technologies later. Or you might want to promote testability in your
system. Many of the built-in Unit of Work implementations from common
persistence tools are difficult to deal with in automated unit testing
scenarios."
The Unit of Work class can have methods to mark entities as modified,
newly created, or deleted. The Unit of Work will also have methods to
commit or roll back all of the changes as well.
The important responsibilities of Unit of Work are,
- To manage transactions.
- To order the database inserts, deletes, and updates.
- To prevent duplicate updates. Inside a single usage of a Unit of Work object, different parts of the code may mark the same Invoice object as changed, but the Unit of Work class will only issue a single UPDATE command to the database.
The value of using a Unit of Work pattern is to free the rest of our
code from these concerns so that you can otherwise concentrate on
business logic.
Why use Unit of Work?
Again Martin Fowler statements, "When you're pulling data in and out of a
database, it's important to keep track of what you've changed;
otherwise, that data won't be written back into the database. Similarly
you have to insert new objects you create and remove any objects you
delete.
You can change the database with each change to your object model, but
this can lead to lots of very small database calls, which ends up being
very slow. Furthermore it requires you to have a transaction open for
the whole interaction, which is impractical if you have a business
transaction that spans multiple requests. The situation is even worse if
you need to keep track of the objects you've read so you can avoid
inconsistent reads.
A Unit of Work keeps track and takes responsibility of everything you do
during a business transaction that can affect the database. When you're
done, it figures out everything that needs to be done to alter the
database as a result of your work."
You see I don’t have to concentrate much on theory, we already have
great definitions existing, all we needed is to stack them in a correct
format.
Using the Unit of Work
One of the best ways to use the Unit of Work pattern is to allow
disparate classes and services to take part in a single logical
transaction. The key point here is that you want the disparate classes
and services to remain ignorant of each other while being able to enlist
in a single transaction. Traditionally, you've been able to do this by
using transaction coordinators like MTS/COM+ or the newer
System.Transactions namespace. Personally, I prefer using the Unit of
Work pattern to allow unrelated classes and services to take part in a
logical transaction because I think it makes the code more explicit,
easier to understand, and simpler to unit test(From MSDN).
Creating a Generic Repository
Cut the Redundancy…
Step 1: Open up our existing MVC3 application created in Part5 in Visual Studio.
Step2: Right click Learning MVC project folder and create a folder named GenericRepository and add a class namedGenericRepository.cs to that folder.
The code of the GenericRepository.cs class is as follows:
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Linq.Expressions;
namespace LearningMVC.GenericRepository
{
public class GenericRepository<TEntity> where TEntity : class
{
internal MVCEntities context;
internal DbSet<TEntity> dbSet;
public GenericRepository(MVCEntities context)
{
this.context = context;
this.dbSet = context.Set<TEntity>();
}
public virtual IEnumerable<TEntity> Get()
{
IQueryable<TEntity> query = dbSet;
return query.ToList();
}
public virtual TEntity GetByID(object id)
{
return dbSet.Find(id);
}
public virtual void Insert(TEntity entity)
{
dbSet.Add(entity);
}
public virtual void Delete(object id)
{
TEntity entityToDelete = dbSet.Find(id);
Delete(entityToDelete);
}
public virtual void Delete(TEntity entityToDelete)
{
if (context.Entry(entityToDelete).State == EntityState.Detached)
{
dbSet.Attach(entityToDelete);
}
dbSet.Remove(entityToDelete);
}
public virtual void Update(TEntity entityToUpdate)
{
dbSet.Attach(entityToUpdate);
context.Entry(entityToUpdate).State = EntityState.Modified;
}
}
}
We can see, we have created the generic methods and the class as well is
generic, when instantiating this class we can pass any model on which
the class will work as a repository and serve the purpose.
TEntity is any model/domain/entity class. MVCEntities is our DBContext as discussed in earlier parts.
Step 3: Implementing UnitOfWork: Create a folder named UnitOfWork under LearningMVC project, and add a class UnitOfWork.cs to that folder.
The code of the class is as follows:
using System;
using LearningMVC.GenericRepository;
namespace LearningMVC.UnitOfWork
{
public class UnitOfWork : IDisposable
{
private MVCEntities context = new MVCEntities();
private GenericRepository<User> userRepository;
public GenericRepository<User> UserRepository
{
get
{
if (this.userRepository == null)
this.userRepository = new GenericRepository<User>(context);
return userRepository;
}
}
public void Save()
{
context.SaveChanges();
}
private bool disposed = false;
protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
context.Dispose();
}
}
this.disposed = true;
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}
}
We see the class implements
IDisposable interface for objects of this class to be disposed.
We create object of
DBContext in this class, note that earlier it was used to be passed in Repository class from a controller.
Now it's time to create our User Repository. We see in the code itself that, simply a variable named
userRepositoryis declared as private GenericRepository<User> userRepository; of type GenericRepository serving User entity to TEntity template.
Then a property is created for the same
userRepository variable in a very simplified manner,public GenericRepository<User> UserRepository
{
get
{
if (this.userRepository == null)
this.userRepository = new GenericRepository<User>(context);
return userRepository;
}
}
I.e., mere 6-7 lines of code. Guess what? Our UserRepository is created.
(Taken from Google)
You see it was as simple as that, you can create as many repositories
you want by just creating simple properties, and no need to create
separate classes. And now you can complete the rest of the story by
yourself, confused???? Yes it's
DBOperations, let's do it.
Step 4: In
MyController, declare a variable unitOfWork as:private UnitOfWork.UnitOfWork unitOfWork = new UnitOfWork.UnitOfWork();
Now this unitOfWork instance of UnitOfWork class holds all th repository
properties,if we press “." After it, it will show the repositories.So
we can choose any of the repositories created and perform CRUD
operations on them.
E.g. our Index action:
public ActionResult Index()
{
var userList = from user in unitOfWork.UserRepository.Get() select user;
var users = new List<LearningMVC.Models.UserList>();
if (userList.Any())
{
foreach (var user in userList)
{
users.Add(new LearningMVC.Models.UserList() { UserId = user.UserId,
Address = user.Address, Company = user.Company,
FirstName = user.FirstName, LastName = user.LastName,
Designation = user.Designation, EMail = user.EMail, PhoneNo = user.PhoneNo });
}
}
ViewBag.FirstName = "My First Name";
ViewData["FirstName"] = "My First Name";
if(TempData.Any())
{
var tempData = TempData["TempData Name"];
}
return View(users);
}
Here,
unitOfWork.UserRepository> AccessingUserRepository.unitOfWork.UserRepository.Get()-> Accessing GenericGet()method to get all users.
Earlier we used to have
MyController constructor like:public MyController()
{
this.userRepository = new UserRepository(new MVCEntities());
}
Now, no need to write that constructor, in fact you can remove the
UserRepository class and Interface we created in part 5 of Learning MVC.
I hope you can write the Actions for rest of the CRUD operations as well.
Details
public ActionResult Details(int id)
{
var userDetails = unitOfWork.UserRepository.GetByID(id);
var user = new LearningMVC.Models.UserList();
if (userDetails != null)
{
user.UserId = userDetails.UserId;
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
}
return View(user);
}
Create:
[HttpPost]
public ActionResult Create(LearningMVC.Models.UserList userDetails)
{
try
{
var user = new User();
if (userDetails != null)
{
user.UserId = userDetails.UserId;
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
}
unitOfWork.UserRepository.Insert(user);
unitOfWork.Save();
return RedirectToAction("Index");
}
catch
{
return View();
}
}
Edit:
public ActionResult Edit(int id)
{
var userDetails = unitOfWork.UserRepository.GetByID(id);
var user = new LearningMVC.Models.UserList();
if (userDetails != null)
{
user.UserId = userDetails.UserId;
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
}
return View(user);
}
[HttpPost]
public ActionResult Edit(int id, User userDetails)
{
TempData["TempData Name"] = "Akhil";
try
{
var user = unitOfWork.UserRepository.GetByID(id);
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
unitOfWork.UserRepository.Update(user);
unitOfWork.Save();
return RedirectToAction("Index");
}
Delete:
public ActionResult Delete(int id)
{
var user = new LearningMVC.Models.UserList();
var userDetails = unitOfWork.UserRepository.GetByID(id);
if (userDetails != null)
{
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
}
return View(user);
}
[HttpPost]
public ActionResult Delete(int id, LearningMVC.Models.UserList userDetails)
{
try
{
var user = unitOfWork.UserRepository.GetByID(id);
if (user != null)
{
unitOfWork.UserRepository.Delete(id);
unitOfWork.Save();
}
return RedirectToAction("Index");
}
catch
{
return View();
}
}
Note: Images are taken from Google images.
Conclusion
We now know how to make generic repositories too, and perform CRUD operations using it.
We have also learnt UnitOfWork pattern in detail. Now you are qualified
and confident enough to apply these concepts in your enterprise
applications. This was the last part of this MVC series, let me know if
you feel to discuss any topic in particular or we can also start any
other series as well. For more informative articles,visit my blog A Practical Approach .
Happy coding :-).
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