（28）ASP.NET Core AutoMapper元件
阿新 • • 發佈：2020-03-13
1.什麼是AutoMapper？
AutoMapper是一個物件-物件對映器。物件-物件對映通過將一種型別的輸入物件轉換為另一種型別的輸出物件來工作。使AutoMapper變得有趣的是，它提供了一些有趣的約定，免去使用者不需要了解如何將型別A對映為型別B。只要型別B遵循AutoMapper既定的約定，就需要幾乎零配置來對映兩個型別。對映程式碼雖然比較無聊，但是AutoMapper為我們提供簡單的型別配置以及簡單的對映測試，而對映可以在應用程式中的許多地方發生，但主要發生在層之間的邊界中，比如，UI /域層之間或服務/域層之間。一層的關注點通常與另一層的關注點衝突，因此物件-物件對映導致分離的模型，其中每一層的關注點僅會影響該層中的型別。
2.如何在Core上面使用AutoMapper元件？
先在Startup.ConfigureServices注入AutoMapper元件服務，然後在Startup.Configure上獲取AutoMapper服務配置擴充套件類建立物件-物件對映關係，為了好統一管理程式碼，可以新建一個AutoMapperExtension靜態類，把以下程式碼封裝一下：
public static class AutoMapperExtension
{
/// <summary>
/// 新增自動對映服務
/// </summary>
/// <param name="service"></param>
/// <returns></returns>
public static IServiceCollection AddAutoMapper(this IServiceCollection services)
{
#region 方案一
//註冊AutoMapper配置擴充套件類服務
services.TryAddSingleton<MapperConfigurationExpression>();
//註冊AutoMapper配置擴充套件類到AutoMapper配置服務去
services.TryAddSingleton(serviceProvider =>
{
var mapperConfigurationExpression = serviceProvider.GetRequiredService<MapperConfigurationExpression>();
var mapperConfiguration = new MapperConfiguration(mapperConfigurationExpression);
mapperConfiguration.AssertConfigurationIsValid();
return mapperConfiguration;
});
//注入IMapper介面DI服務
services.TryAddSingleton(serviceProvider =>
{
var mapperConfiguration = serviceProvider.GetRequiredService<MapperConfiguration>();
return mapperConfiguration.CreateMapper();
});
return services;
#endregion
}
/// <summary>
/// 使用自動對映配置擴充套件類
/// </summary>
/// <param name="applicationBuilder"></param>
/// <returns></returns>
public static IMapperConfigurationExpression UseAutoMapper(this IApplicationBuilder applicationBuilder)
{
//獲取已註冊服務AutoMapper配置擴充套件類
return applicationBuilder.ApplicationServices.GetRequiredService<MapperConfigurationExpression>();
}
}
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
......
//新增自動對映元件DI服務
services.AddAutoMapper();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
......
//註冊元件之後，建立對映物件
var expression = app.UseAutoMapper();
expression.CreateMap<Customer, CustomerDto>();
expression.CreateMap<Address, AddressDto>();
}因為IMapper介面已經在ConfigureServices方法注入DI服務了，所以無需再重新注入，只需要直接使用IMapper呼叫其方法就可以：
public class BlogsController : Controller
{
private IMapper _iMapper { get; }
public BlogsController(IMapper iMapper)
{
_iMapper = iMapper;
}
// GET: Blogs
public async Task<IActionResult> Index()
{
//物件-物件資料傳輸
var dto = _iMapper.Map<CustomerDto>(CustomerInitialize());
......
}
//手動賦值客戶物件資料
private Customer CustomerInitialize()
{
var _customer = new Customer()
{
Id = 1,
Name = "Eduardo Najera",
Credit = 234.7m,
Address = new Address() { City = "istanbul", Country = "turkey", Id = 1, Street = "istiklal cad." },
HomeAddress = new Address() { City = "istanbul", Country = "turkey", Id = 2, Street = "istiklal cad." },
WorkAddresses = new List<Address>()
{
new Address() {City = "istanbul", Country = "turkey", Id = 5, Street = "istiklal cad."},
new Address() {City = "izmir", Country = "turkey", Id = 6, Street = "konak"}
},
Addresses = new List<Address>()
{
new Address() {City = "istanbul", Country = "turkey", Id = 3, Street = "istiklal cad."},
new Address() {City = "izmir", Country = "turkey", Id = 4, Street = "konak"}
}.ToArray()
};
return _customer;
}
}執行效果：
3.如果更加靈活使用AutoMapper元件？
相信在第二章節時候，相信大家都會發現一個問題，如果生產場景業務越來越龐大，需建立對應業務物件也會越來越多，如果面對這樣的業務場景難道要在Configure方法裡面建立越來越多的對映關係嗎？例：
var expression = app.UseAutoMapper(); expression.CreateMap<A, ADto>(); expression.CreateMap<B, BDto>(); expression.CreateMap<C, CDto>(); expression.CreateMap<D, DDto>(); ......
很顯然這樣子是不可行的，這樣會導致後續程式碼越來越多，難以維護。那麼現在讓我們來解決這個問題。首先新建一個自動注入屬性的AutoInjectAttribute密封類，具體程式碼如下：
public sealed class AutoInjectAttribute : Attribute
{
public Type SourceType { get; }
public Type TargetType { get; }
public AutoInjectAttribute(Type sourceType, Type targetType)
{
SourceType = sourceType;
TargetType = targetType;
}
}
新增這個AutoInjectAttribute密封類，目的是宣告每個DTO物件（資料傳輸物件）與對應資料來源物件是傳輸關係，方便在Configure裡面自動註冊建立對映關係，例：
//宣告源物件，目標物件
[AutoInject(sourceType: typeof(Customer),targetType:typeof(CustomerDto))]
public class CustomerDto
{
public int Id { get; set; }
public string Name { get; set; }
public Address Address { get; set; }
public AddressDto HomeAddress { get; set; }
public AddressDto[] Addresses { get; set; }
public List<AddressDto> WorkAddresses { get; set; }
public string AddressCity { get; set; }
}
然後建立一個自動注入AutoInjectFactory工廠類，檢測執行中的程式集是否有AutoInjectAttribute屬性宣告，如果有則插入一個型別資料集中返回，目的是把所有宣告需要對映DTO物件跟資料來源物件自動建立對映關係：
public class AutoInjectFactory
{
public List<(Type, Type)> AddAssemblys
{
get
{
var assemblys =new List<Assembly>() { Assembly.GetExecutingAssembly() };
List<(Type, Type)> ConvertList = new List<(Type, Type)>();
foreach (var assembly in assemblys)
{
var atributes = assembly.GetTypes()
.Where(_type => _type.GetCustomAttribute<AutoInjectAttribute>() != null)
.Select(_type => _type.GetCustomAttribute<AutoInjectAttribute>());
foreach (var atribute in atributes)
{
ConvertList.Add((atribute.SourceType, atribute.TargetType));
}
}
return ConvertList;
}
}
}
在第2小節AutoMapperExtension靜態類的AddAutoMapper方法內修改如下程式碼：
#region 方案二
//注入AutoMapper配置擴充套件類服務
services.TryAddSingleton<MapperConfigurationExpression>();
//注入自動注入工廠類服務
services.TryAddSingleton<AutoInjectFactory>();
//注入AutoMapper配置擴充套件類到AutoMapper配置服務去
services.TryAddSingleton(serviceProvider =>
{
var mapperConfigurationExpression = serviceProvider.GetRequiredService<MapperConfigurationExpression>();
//通過自動注入工廠類獲取宣告資料來源物件與DTO物件自動建立對映關係
var factory = serviceProvider.GetRequiredService<AutoInjectFactory>();
foreach (var (sourceType, targetType) in factory.AddAssemblys)
{
mapperConfigurationExpression.CreateMap(sourceType, targetType);
}
var mapperConfiguration = new MapperConfiguration(mapperConfigurationExpression);
mapperConfiguration.AssertConfigurationIsValid();
return mapperConfiguration;
});
//注入IMapper介面DI服務
services.TryAddSingleton(serviceProvider =>
{
var mapperConfiguration = serviceProvider.GetRequiredService<MapperConfiguration>();
return mapperConfiguration.CreateMapper();
});
return services;
#endregion
再新增一個使用自動注入工廠類服務靜態方法：
/// <summary>
/// 使用自動注入工廠類
/// </summary>
/// <param name="applicationBuilder"></param>
public static void UseAutoInject(this IApplicationBuilder applicationBuilder)
{
applicationBuilder.ApplicationServices.GetRequiredService<AutoInjectFactory>();
}
然後在Startup.ConfigureServices注入AutoMapper元件服務，然後在Startup.Configure上呼叫UseAutoInject靜態方法，具體程式碼如下：
app.UseAutoInject();
執行效果：
從執行結果來看依然是這個酸爽！
參考文獻：
AutoMa