（28）ASP.NET Core AutoMapper組件-有解無憂

1.什么是AutoMapper？

AutoMapper是一個物件-物件映射器，物件-物件映射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作業，使AutoMapper變得有趣的是，它提供了一些有趣的約定，免去用戶不需要了解如何將型別A映射為型別B，只要型別B遵循AutoMapper既定的約定，就需要幾乎零配置來映射兩個型別，映射代碼雖然比較無聊，但是AutoMapper為我們提供簡單的型別配置以及簡單的映射測驗，而映射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沖突，因此物件-物件映射導致分離的模型，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組件？

先在Startup.ConfigureServices注入AutoMapper組件服務，然后在Startup.Configure上獲取AutoMapper服務配置擴展類創建物件-物件映射關系，為了好統一管理代碼，可以新建一個AutoMapperExtension靜態類，把以下代碼封裝一下：

public static class AutoMapperExtension
{
    /// <summary>
    /// 新增自動映射服務
    /// </summary>
    /// <param name="service"></param>
    /// <returns></returns>
    public static IServiceCollection AddAutoMapper(this IServiceCollection services)
    {
        #region 方案一
        //注冊AutoMapper配置擴展類服務
        services.TryAddSingleton<MapperConfigurationExpression>();
        //注冊AutoMapper配置擴展類到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>
    /// 使用自動映射配置擴展類
    /// </summary>
    /// <param name="applicationBuilder"></param>
    /// <returns></returns>
    public static IMapperConfigurationExpression UseAutoMapper(this IApplicationBuilder applicationBuilder)
    {
        //獲取已注冊服務AutoMapper配置擴展類
        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)
{
    ......
    //添加自動映射組件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)
{
    ......
    //注冊組件之后，創建映射物件
　　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;
    }
}

運行效果：

3.如果更加靈活使用AutoMapper組件？

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，需創建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方法里面創建越來越多的映射關系嗎？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，這樣會導致后續代碼越來越多，難以維護，那么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，具體代碼如下：

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）與對應資料源物件是傳輸關系，方便在Configure里面自動注冊創建映射關系，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; }
}

然后創建一個自動注入AutoInjectFactory工廠類，檢測運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回傳，目的是把所有宣告需要映射DTO物件跟資料源物件自動創建映射關系：

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方法內修改如下代碼：

#region 方案二
//注入AutoMapper配置擴展類服務
services.TryAddSingleton<MapperConfigurationExpression>();
//注入自動注入工廠類服務
services.TryAddSingleton<AutoInjectFactory>();
//注入AutoMapper配置擴展類到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源物件與DTO物件自動創建映射關系
    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>();
}

然后在Startup.ConfigureServices注入AutoMapper組件服務，然后在Startup.Configure上呼叫UseAutoInject靜態方法，具體代碼如下：

app.UseAutoInject();

運行效果：

從運行結果來看依然是這個酸爽！

參考文獻：
AutoMapper

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標籤：.NET Core

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