ASP.NET?Core使用AutoMapper組件

更新時間：2022年04月08日 10:30:38 作者：暗斷腸

這篇文章介紹了ASP.NET?Core使用AutoMapper組件的方法，文中通過示例代碼介紹的非常詳細(xì)。對大家的學(xué)習(xí)或工作具有一定的參考借鑒價值，需要的朋友可以參考下

1.什么是AutoMapper？

AutoMapper是一個對象-對象映射器。對象-對象映射通過將一種類型的輸入對象轉(zhuǎn)換為另一種類型的輸出對象來工作。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類型A映射為類型B。只要類型B遵循AutoMapper既定的約定，就需要幾乎零配置來映射兩個類型。映射代碼雖然比較無聊，但是AutoMapper為我們提供簡單的類型配置以及簡單的映射測試，而映射可以在應(yīng)用程序中的許多地方發(fā)生，但主要發(fā)生在層之間的邊界中，比如，UI /域?qū)又g或服務(wù)/域?qū)又g。一層的關(guān)注點通常與另一層的關(guān)注點沖突，因此對象-對象映射導(dǎo)致分離的模型，其中每一層的關(guān)注點僅會影響該層中的類型。

2.如何在Core上面使用AutoMapper組件？

先在Startup.ConfigureServices注入AutoMapper組件服務(wù)，然后在Startup.Configure上獲取AutoMapper服務(wù)配置擴展類創(chuàng)建對象-對象映射關(guān)系，為了好統(tǒng)一管理代碼，可以新建一個AutoMapperExtension靜態(tài)類，把以下代碼封裝一下：

public static class AutoMapperExtension
{
    /// <summary>
    /// 新增自動映射服務(wù)
    /// </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(wù)
        services.TryAddSingleton<MapperConfigurationExpression>();
        //注冊AutoMapper配置擴展類到AutoMapper配置服務(wù)去
        services.TryAddSingleton(serviceProvider =>
        {
            var mapperConfigurationExpression = serviceProvider.GetRequiredService<MapperConfigurationExpression>();
            var mapperConfiguration = new MapperConfiguration(mapperConfigurationExpression);
            mapperConfiguration.AssertConfigurationIsValid();
            return mapperConfiguration;
        });
        //注入IMapper接口DI服務(wù)
        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(wù)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(wù)
    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(chuàng)建映射對象
　　var expression = app.UseAutoMapper();
    expression.CreateMap<Customer, CustomerDto>();
    expression.CreateMap<Address, AddressDto>();
}

因為IMapper接口已經(jīng)在ConfigureServices方法注入DI服務(wù)了，所以無需再重新注入，只需要直接使用IMapper調(diào)用其方法就可以：

public class BlogsController : Controller
{
    private IMapper _iMapper { get; }
    public BlogsController(IMapper iMapper)
    {
        _iMapper = iMapper;
    }
    // GET: Blogs
    public async Task<IActionResult> Index()
    {
    //對象-對象數(shù)據(jù)傳輸
        var dto = _iMapper.Map<CustomerDto>(CustomerInitialize());
        ......
    }
    //手動賦值客戶對象數(shù)據(jù)
    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(jié)時候，相信大家都會發(fā)現(xiàn)一個問題，如果生產(chǎn)場景業(yè)務(wù)越來越龐大，需創(chuàng)建對應(yīng)業(yè)務(wù)對象也會越來越多，如果面對這樣的業(yè)務(wù)場景難道要在Configure方法里面創(chuàng)建越來越多的映射關(guān)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(dǎo)致后續(xù)代碼越來越多，難以維護(hù)。那么現(xiàn)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，目的是聲明每個DTO對象（數(shù)據(jù)傳輸對象）與對應(yīng)數(shù)據(jù)源對象是傳輸關(guān)系，方便在Configure里面自動注冊創(chuàng)建映射關(guān)系，例：

//聲明源對象，目標(biāo)對象
[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(chuàng)建一個自動注入AutoInjectFactory工廠類，檢測運行中的程序集是否有AutoInjectAttribute屬性聲明，如果有則插入一個類型數(shù)據(jù)集中返回，目的是把所有聲明需要映射DTO對象跟數(shù)據(jù)源對象自動創(chuàng)建映射關(guān)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(jié)AutoMapperExtension靜態(tài)類的AddAutoMapper方法內(nèi)修改如下代碼：

#region 方案二
//注入AutoMapper配置擴展類服務(wù)
services.TryAddSingleton<MapperConfigurationExpression>();
//注入自動注入工廠類服務(wù)
services.TryAddSingleton<AutoInjectFactory>();
//注入AutoMapper配置擴展類到AutoMapper配置服務(wù)去
services.TryAddSingleton(serviceProvider =>
{
    var mapperConfigurationExpression = serviceProvider.GetRequiredService<MapperConfigurationExpression>();
    //通過自動注入工廠類獲取聲明數(shù)據(jù)源對象與DTO對象自動創(chuàng)建映射關(guān)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接口DI服務(wù)
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(wù)靜態(tài)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(wù)，然后在Startup.Configure上調(diào)用UseAutoInject靜態(tài)方法，具體代碼如下：