The Problem
Have you ever faced need to write code, which looks like here:
Customer customer = GetCustomerFromDB();
CustomerViewItem customerViewItem = new CustomerViewItem()
{
FirstName = customer.FirstName,
LastName = customer.LastName,
DateOfBirth = customer.DateOfBirth,
NumberOfOrders = customer.NumberOfOrders
};
ShowCustomerInDataGrid(customerViewItem);
Our scenario could be like:
We have our domain model which has
Customer entity and we are going to show Customers in DataGrid, and for that we need much lighter object
CustomerViewItem, list of which is bounded to the Grid.
As you see there are four lines of code which are just copying values from one object to another. Could also be that you will need to show up to 10-15 columns in you grid. What then?
Would you like to have something that will do mapping from
Customer to the
CustomerViewItem automatically?
Of course you do, especially if you have another situation like mapping of heavy data objects into DTO objects which are considered to be send though the wire.
AutoMapper
From the AutoMapper codeplex web page we see that "
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 convention, almost zero configuration is needed to map two types.", so in other words it provides the solution for our problem.
To get started go and download it
here. It is standalone assembly, so you should not get difficulties with including reference to it in your project.
So in order to ask AutoMapper do dirty work instead of me, we need to add next line somewhere in the start of our code execution:
Mapper.CreateMap<Customer, CustomerViewItem>();
Once we have that we are done and we can use pretty nice code to get our mapped object:
Customer customer = GetCustomerFromDB();
CustomerViewItem customerViewItem = Mapper.Map<Customer, CustomerViewItem>(customer);
ShowCustomerInDataGrid(customerViewItem);
Lets take a look on whole code base to see all about what I'm going to talk further:
class Program
{
static void Main(string[] args)
{
var program = new Program();
Mapper.CreateMap<Customer, CustomerViewItem>();
program.Run();
}
private void Run()
{
Customer customer = GetCustomerFromDB();
CustomerViewItem customerViewItem = Mapper.Map<Customer, CustomerViewItem>(customer);
ShowCustomerInDataGrid(customerViewItem);
}
private void ShowCustomerInDataGrid(CustomerViewItem customerViewItem){}
private Customer GetCustomerFromDB()
{
return new Customer()
{
DateOfBirth = new DateTime(1987, 11, 2),
FirstName = "Andriy",
LastName = "Buday",
NumberOfOrders = 7
};
}
}
public class Customer
{
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime DateOfBirth { get; set; }
public int NumberOfOrders { get; set; }
}
public class CustomerViewItem
{
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime DateOfBirth { get; set; }
public int NumberOfOrders { get; set; }
}
And proving that all values has been mapped take a look on the picture:
More Complex Example 1 (Custom Map)
So far we know all to have extremely simple mapping. But what if we need something more complex, for example,
CustomerViewItem should have
FullName, which consists with First and Last names of
Customer?
After I just added
public string FullName { get; set; } to the
CustomerViewItem and run my application in debug I got null value in that property. That is fine and is because AutoMapper doesn't see any
FullName property in
Customer class. In order to "open eyes" all you need is just to change a bit our CreateMap process:
Mapper.CreateMap<Customer, CustomerViewItem>()
.ForMember(cv => cv.FullName, m => m.MapFrom(s => s.FirstName + " " + s.LastName))
And results are immediately:
More Complex Example 2 (Flattening)
What if you have property
Company of type
Company:
public class Customer
{
public Company Company { get; set; }
//...
}
public class Company
{
public string Name { get; set; }
}
and want to map it into
CompanyName of the view class
public class CustomerViewItem
{
public string CompanyName { get; set; }
//...
}
How do you think what do you need to change in your mapping to make this work?
Answer:
NOTHING. AutoMapper goes in deep of your classes and if names matches it will do mapping for you.
More Complex Example 3 (Custom type resolvers)
What if you have boolean property
VIP in your Customer class:
public class Customer
{
public bool VIP { get; set; }
}
and want to map it into string
VIP and represent like "Y" or "N" instead
public class CustomerViewItem
{
public string VIP { get; set; }
}
Well, we can solve this the same way we did for the
FullName, but more appropriate way is to use custom resolvers.
So lets create customer resolver which will resolve VIP issue for us.
It looks like:
public class VIPResolver : ValueResolver<bool , string >
{
protected override string ResolveCore(bool source)
{
return source ? "Y" : "N";
}
}
And only one line is needed for our CreateMap process:
.ForMember(cv => cv.VIP, m => m.ResolveUsing<VIPResolver>().FromMember(x => x.VIP));
More Complex Example 4 (Custom Formatters)
What if I want AutoMapper to use my custom formatting of the
DateTime instead of just using
ToString, when it does mapping from DateTime to String property?
Let say I want use
ToLongDateString method to show birth date with fashion.
For that we add:
public class DateFormatter:IValueFormatter
{
public string FormatValue(ResolutionContext context)
{
return ((DateTime) context.SourceValue).ToLongDateString();
}
}
And making sure that AutoMapper knows where to use it:
.ForMember(cv => cv.DateOfBirth, m => m.AddFormatter<DateFormatter>());
So, now I've got:
Great, isn't it? BirthDate is even in my native language.
I hope my article was interesting to read and it gave you ideas how you can utilize this new feature called "AutoMapper".
![image_thumb[1]](http://lh6.ggpht.com/_kD34xgIwKhc/TWPRIAfSOEI/AAAAAAAAB9o/dug4ifhAynU/MCPD%28rgb%29_1260_thumb.png "image_thumb[1]")
