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4. Object mapping Mapstercover

2022-07-02 00:03:00 【InfoQ】

Preface

We often encounter object mapping in projects , Such as Model and Dto Mapping between , Or a deep copy of an object , We need to realize these by ourselves . here , There will be a lot of code for initializing objects in the project , The code is pretty boring to write , Is there any way to reduce our workload , So that we can spend time on business functions ？

at present ,.Net Object mapping framework in , Powerful and excellent object mapping frameworks already exist , The most used ones are :

Mapster

AutoMapper

Speaking of the object mapping framework , What people think of most is

AutoMapper

, Maybe a lot of people

Mapster

Never heard of it , But there's no denying it

Mapster

It is really a good object mapping framework , However, due to the lack of Chinese documents , As a result, the popularity in China is not very high , Today we will introduce

Mapster

What functions are provided , How to use it in a project ,

Masa

Provided

Mapster

What else has been done ？

Mapster brief introduction

Mapster

It's a simple to use , Powerful object mapping framework , since 2014 It's past since the year of open source 8 A year , Up to now ,github I already have 2.6k Of star, And keep it every year 3 Distribution frequency of times , Its function and AutoMapper similar , Provide object to object mapping 、 And support IQueryable Mapping to objects , And

AutoMapper

comparison , Better performance in terms of speed and memory usage , You can only use 1/3 In the case of memory 4 Times performance improvement , Let's take a look at

Mapster

How to use ？

preparation

Create a new console project
Assignment.Mapster
, And install
Mapster

 dotnet add package Mapster --version 7.3.0

Map to new object

The new class
UserDto

 public class UserDto
 {
 public int Id { get; set; }
 
 public string Name { get; set; }
 
 public uint Gender { get; set; }
 
 public DateTime BirthDay { get; set; }
 }

Create a new anonymous object , As the source of the object to be converted

 var user = new
 {
 Id = 1,
 Name = &quot;Tom&quot;,
 Gender = 1,
 BirthDay = DateTime.Parse(&quot;2002-01-01&quot;)
 };

take user The source object is mapped to the target object (UserDto)

 var userDto = user.Adapt<UserDto>();
 Console.WriteLine($&quot; Map to new object ,Name: {userDto.Name}&quot;);

Run the console program to verify that the conversion is successful :

data type

In addition to providing object-to-object mapping , It also supports data type conversion , Such as ：

Basic types

Provide the function of type mapping , similar Convert.ChangeType()

 string res = &quot;123&quot;;
 decimal i = res.Adapt<decimal>(); //equal to (decimal)123;
 Console.WriteLine($&quot; The result is ：{i == int.Parse(res)}&quot;);

Run the console program :

Enumeration type

Map enumerations to numeric types , It also supports string to enumeration and enumeration to string mapping , Than .NET The default implementation of is twice as fast

 var fileMode = &quot;Create, Open&quot;.Adapt<FileMode>();// be equal to  FileMode.Create | FileMode.Open
 Console.WriteLine($&quot; The result of enumeration type conversion is ：{fileMode == (FileMode.Create | FileMode.Open)}&quot;);

Run the console program to verify that the conversion is successful :

Queryable Expand

Mapster Provides Queryable An extension of , Used to implement DbContext On demand lookup for , for example :

The new class
UserDbContext

 using Assignment.Mapster.Domain;
 using Microsoft.EntityFrameworkCore;
 
 namespace Assignment.Mapster.Infrastructure;
 
 public class UserDbContext : DbContext
 {
 public DbSet<User> User { get; set; }
 
 protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
 {
 var dataBaseName = Guid.NewGuid().ToString();
 optionsBuilder.UseInMemoryDatabase(dataBaseName);// Use memory database , Convenient test 
 }
 }

The new class
User

 public class User
 {
 public int Id { get; set; }
 
 public string Name { get; set; }
 
 public uint Gender { get; set; }
 
 public DateTime BirthDay { get; set; }
 
 public DateTime CreationTime { get; set; }
 
 public User()
 {
 CreationTime = DateTime.Now;
 }
 }

Using a Queryable Extension method of
ProjectToType

 using (var dbContext = new UserDbContext())
 {
 dbContext.Database.EnsureCreated();
 
 dbContext.User.Add(new User()
 {
 Id = 1,
 Name = &quot;Tom&quot;,
 Gender = 1,
 BirthDay = DateTime.Parse(&quot;2002-01-01&quot;)
 });
 dbContext.SaveChanges();
 
 var userItemList = dbContext.User.ProjectToType<UserDto>().ToList();
 }

Run the console program to verify that the conversion is successful :

besides ,

Mapster

Pre mapping is also provided / post-processing , Copy and merge and mapping configuration nesting support , Details can be viewed

file

, since

Mapster

Already so powerful , Then I can use it directly , Why even use

Masa

Provided Mapper Well ？

What is? Masa.Contrib.Data.Mapping.Mapster？

Masa.Contrib.Data.Mapping.Mapster

Is based on

Mapster

An object to object mapper for , And in the original

Mapster

Add auto get and use best constructor mapping based on , Support nested mapping , Reduce the workload of mapping .

Mapping rule

When the target object does not have a constructor ： Use an empty constructor , Mapping to fields and attributes .

Multiple constructors exist for the target object ： Get the best constructor mapping

Best constructor : The number of constructor parameters of the target object is found in descending order , The parameter names are consistent （ Case insensitive ） And the parameter type is consistent with the source object attribute

preparation

Create a new console project
Assignment.Masa.Mapster
, And install
Masa.Contrib.Data.Mapping.Mapster
,
Microsoft.Extensions.DependencyInjection

 dotnet add package Masa.Contrib.Data.Mapping.Mapster --version 0.4.0-rc.4
 dotnet add package Microsoft.Extensions.DependencyInjection --version 6.0.0

The new class
OrderItem

 public class OrderItem
 {
 public string Name { get; set; }
 
 public decimal Price { get; set; }
 
 public int Number { get; set; }
 
 public OrderItem(string name, decimal price) : this(name, price, 1)
 {
 
 }
 
 public OrderItem(string name, decimal price, int number)
 {
 Name = name;
 Price = price;
 Number = number;
 }
 }

The new class
Order

 public class Order
 {
 public string Name { get; set; }
 
 public decimal TotalPrice { get; set; }
 
 public List<OrderItem> OrderItems { get; set; }
 
 public Order(string name)
 {
 Name = name;
 }
 
 public Order(string name, OrderItem orderItem) : this(name)
 {
 OrderItems = new List<OrderItem> { orderItem };
 TotalPrice = OrderItems.Sum(item => item.Price * item.Number);
 }
 }

Modify the class
Program

 using Assignment.Masa.Mapster.Domain.Aggregate;
 using Masa.BuildingBlocks.Data.Mapping;
 using Masa.Contrib.Data.Mapping.Mapster;
 using Microsoft.Extensions.DependencyInjection;
 
 Console.WriteLine(&quot;Hello Masa Mapster!&quot;);
 
 IServiceCollection services = new ServiceCollection();
 services.AddMapping();
 
 var request = new
 {
 Name = &quot;Teach you to learn Dapr ……&quot;,
 OrderItem = new OrderItem(&quot;Teach you to learn Dapr hand by hand&quot;, 49.9m)
 };
 var serviceProvider = services.BuildServiceProvider();
 var mapper = serviceProvider.GetRequiredService<IMapper>();
 var order = mapper.Map<Order>(request);
 
 Console.WriteLine($&quot;{nameof(Order.TotalPrice)} is {order.TotalPrice}&quot;);// Console output 49.9
 
 Console.ReadKey();

If the conversion is successful ,TotalPrice The value should be 49.9, Then we run the console program to verify whether the conversion is successful ：

How to achieve

We mentioned above

Masa.Contrib.Data.Mapping.Mapster

You can automatically get and use the best constructor mapping , And then complete the object to object mapping , So how does it come true ？ Will it affect the performance ？

It is used to automatically obtain and use the best constructor mapping

Mapster

The function of constructor mapping provided by , By specifying the constructor , Complete object to object mapping .

see
file

summary

at present

Masa.Contrib.Data.Mapping.Mapster

Its function is relatively weak , The current version is similar to

Mapster

It only adds a function of automatically obtaining and using the best constructor , Let's easily complete the mapping when facing a class that has no empty constructor and has multiple constructors , There is no need to write an extra line of code .

But I think

Masa

Version of Mapping The biggest benefit is that the project depends on

BuildingBlocks

Under the

IMapper

, instead of

Mapster

, This makes our project separate from the specific mapper implementation , If we are asked that the project must use

AutoMapper

, Just implement

AutoMapper