Introduction
In our article series of Learning MVC, we learnt a lot about MVC, about various techniques to communicate to a database in MVC applications, and a few internal concepts too.
When we indulge into real-time programming environments, we face not only one but many types of challenges in the code. This article explains a new concept, Auto Mapper in MVC applications, to overcome one of the major challenges we face while communicating with data entities and binding them to our model.
Challenge
Sometimes while interacting with real time (database) entities and binding our model to them, we end up in a situation like:
var dbContext = new MyDBDataContext();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == id);
var user = new LearningMVC.Models.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;
}
return View(user);
The above mentioned code is not very hard to understand. In the above code, an instance var dbContext = new MyDBDataContext(); is created from the LINQ to SQL Context class, thereafter the user details are fetched from a user specific table and stored in the var userDetails variable. We have an existing model named User (LearningMVC.Models.User()) that has similar properties as that of the Users class generated from the database. Now we initialize properties of the instance of our model from properties of instance of the User class from the database so that we can populate our View in an MVC application.
We see here that there are eight properties that are similar to each other but each set lies in a separate class, one in the Model, and one in the Users class. And what we do is one by one we bind these properties to our model and pass it to the View. Now the problem is what if we have 100 column records coming from the database, and also our model has the same number of properties, and the code has to be repeated 6-7 times at different scenarios? Now do we still follow such a strategy of binding each property from the database to the model? Trust me, the code will be 100 pages large, and will be charging five times the effort just to bind the model from the domain entities.
To overcome this tedious situation AutoMapper is introduced. It not only reduces the effort, but also limits the execution time that has been taken by such a large number of lines to execute.
Auto Mapper
AutoMapper is an open source library provided in GitHub.
As per the AutoMapper CodePlex webpage: "AutoMapper is an object-object mapper. Object-object mapping works by transforming an input object of one type into an output object of a different type. What makes AutoMapper interesting is that it provides some interesting conventions to take the dirty work out of figuring out how to map type A to type B. As long as type B follows AutoMapper's established conventions, almost zero configuration is needed to map two types." Therefore, it provides the solution for our mapping issue.
Install AutoMapper
Firstly install the NuGet Package Manager in your Visual Studio IDE. Once done, go to:
Tools -> Library Packet Manager -> Packet manager Console
Then in the console window opened at the bottom of Visual Studio, type:
PM> Install-Package AutoMapper
Press Enter, this will install AutoMapper and the next time you open an MVC application in Visual Studio, it will automatically add a DLL reference to the project.
AutoMapper in Action
Let's create an MVC application first. You can create an MVC application and connect it with the database using LINQ to SQL following my article: http://www.codeproject.com/Articles/620197/Learning-MVC-Part-2-Creating-MVC-Application-and-P
I have also attached the code for an existing MVC application used without AutoMapper. Now let’s evaluate all the Controller Actions one by one and convert the code using AutoMapper.
Step 1: Create a database for the existing application, the database script is attached with the source code:
Open the existing MVC application in Visual Studio:
See that AutoMapper is referenced in the project, now use that namespace in MyController, as:
Step 2: Index Action:
In the very first Action of our controller MyController (found under the Controllers folder), Index Action, we see the code:
public ActionResult Index()
{
var dbContext = new MyDBDataContext();
var userList = from user in dbContext.Users select user;
var users = new List<LearningMVC.Models.User>();
if (userList.Any())
{
foreach (var user in userList)
{
users.Add(new LearningMVC.Models.User()
{
UserId = user.UserId,
Address = user.Address,
Company = user.Company,
FirstName = user.FirstName,
LastName = user.LastName,
Designation = user.Designation,
EMail = user.EMail,
PhoneNo = user.PhoneNo
});
}
}
return View(users);
}
Now where will AutoMapper fit in here? You know that it will be used to replace the property mapping done one by one in the code, therefore, at the first line of code, define an AutoMap. To create the default mapping, call Mapper.CreateMap<T1, T2>() with proper types. In this case, T1 will be LearningMVC.User and T2 will be LearningMVC.Models.User.
Mapper.CreateMap<LearningMVC.User, LearningMVC.Models.User>();
- LearningMVC.User -> DTO Object Class
- LearningMVC.Models.User -> Model Class to bind the View
So, here we define a mapping between DTO and the Model class with the help of the AutoMapper class.
Now inside the foreach loop, replace the whole code by:
LearningMVC.Models.User userModel = Mapper.Map<LearningMVC.User, LearningMVC.Models.User>(user);
users.Add(userModel);
Finally call the Mapper.Map<T1, T2>(obj1) to get the mapped object of T2.
So, our final Action code:
public ActionResult Index()
{
Mapper.CreateMap<LearningMVC.User, LearningMVC.Models.User>();
var dbContext = new MyDBDataContext();
var userList = from user in dbContext.Users select user;
var users = new List<LearningMVC.Models.User>();
if (userList.Any())
{
foreach (var user in userList)
{
LearningMVC.Models.User userModel =
Mapper.Map<LearningMVC.User, LearningMVC.Models.User>(user);
users.Add(userModel);
}
}
return View(users);
}
We see now, we escaped the boring work of matching properties one by one. Now run the application, and you’ll see the application running as before.
Step 3: Details Action:
Existing code
public ActionResult Details(int? id)
{
var dbContext = new MyDBDataContext();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == id);
var user = new LearningMVC.Models.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;
}
return View(user);
}
New code with AutoMapper
public ActionResult Details(int? id)
{
var dbContext = new MyDBDataContext();
Mapper.CreateMap<LearningMVC.User, LearningMVC.Models.User>();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == id);
LearningMVC.Models.User user =
Mapper.Map<LearningMVC.User, LearningMVC.Models.User>(userDetails);
return View(user);
}
Step 4: Create Action (POST)
Existing code:
[HttpPost]
public ActionResult Create(LearningMVC.Models.User userDetails)
{
try
{
var dbContext = new MyDBDataContext();
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;
}
dbContext.Users.InsertOnSubmit(user);
dbContext.SubmitChanges();
return RedirectToAction("Index");
}
catch
{
return View();
}
}
New code with AutoMapper:
[HttpPost]
public ActionResult Create(LearningMVC.Models.User userDetails)
{
try
{
Mapper.CreateMap<LearningMVC.Models.User, LearningMVC.User>();
var dbContext = new MyDBDataContext();
var user = Mapper.Map<LearningMVC.Models.User, LearningMVC.User>(userDetails);
dbContext.Users.InsertOnSubmit(user);
dbContext.SubmitChanges();
return RedirectToAction("Index");
}
catch
{
return View();
}
}
Note that, in here we interchange the mapping because now we have to read from the Model and bind to our DTO for Create Action, so just interchange the mapping and run the application. Now our T1 is Model and T2 is DTO.
Step 5: Edit Action:
Existing Code
public ActionResult Edit(int? id)
{
var dbContext = new MyDBDataContext();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == id);
var user = new LearningMVC.Models.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;
}
return View(user);
}
New code with AutoMapper
public ActionResult Edit(int? id)
{
Mapper.CreateMap<LearningMVC.User, LearningMVC.Models.User>();
var dbContext = new MyDBDataContext();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == id);
var user = Mapper.Map<LearningMVC.User, LearningMVC.Models.User>(userDetails)
return View(user);
}
Step 6: Delete Action:
Existing code
public ActionResult Delete(int? id)
{
var dbContext = new MyDBDataContext();
var user = new LearningMVC.Models.User();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == 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);
}
New code using AutoMapper
public ActionResult Delete(int? id)
{
var dbContext = new MyDBDataContext();
Mapper.CreateMap<LearningMVC.User, LearningMVC.Models.User>();
var userDetails = dbContext.Users.FirstOrDefault(userId => userId.UserId == id);
var user = Mapper.Map<LearningMVC.User, LearningMVC.Models.User>(userDetails);
return View(user);
}
ForMember() and MapFrom() in AutoMapper
Two important functions in AutoMapper play an important role in object mapping. Suppose our model/viewmodel class has a property FullName, and from the DTO we want to add the First Name and Last Name of the user to make it a full name and bind it to the model. For these kinds of scenarios ForMember() and MapFrom() come in handy. See below code:
Mapper.CreateMap<LearningMVC.User, LearningMVC.Models.User>().ForMember(emp => emp.Fullname,
map => map.MapFrom(p => p.FirstName + " " + p.LastName));
Here we are saying that ForMember FullName in our model class maps properties from FirstName and LastName of User DTO.
The code itself is self-explanatory. This kind of mapping is also called Custom Mapping.
Conclusion
In this article we learnt how to do custom mapping and entity to entity mapping with the help of AutoMapper. Since this was just a glimpse of the concept there is a lot more to explore in this topic in detail.
I have skipped the POST methods for Edit and Delete, this will be a kind of homework for you. Once you completely follow and understand, you can easily complete those two pending Actions as well.
Happy coding!
