ASP.NET Core 中的物件對映之 AutoMapper

weixin_30823227發表於2018-11-13
ASP.NET物件APP

目錄

AutoMapper 簡介

AutoMapper是一個物件對映器，它可以將一種型別的物件轉換為另一種型別的物件。

它提供了對映規則及操作方法，使我們不用過多配置就可以對映兩個類, 可以幫我們免於編寫無聊的對映程式碼. 在程式碼層與層之間隔離模型model上非常有用.

AutoMapper 使用

初始化

建立兩個簡單的類用於測試:

public class UserEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class UserDTO
{
    public int Id { get; set; }
    public string Name { get; set; }
}

AutoMapper可以使用靜態類和例項方法來建立對映.

  • 靜態類方式

    Mapper.Initialize(cfg => cfg.CreateMap<UserEntity, UserDTO>());
var userDTO = Mapper.Map<UserDTO>(user);

  • 例項方式

    var config = new MapperConfiguration(cfg => cfg.CreateMap<UserEntity, UserDTO>());
var mapper = config.CreateMapper();

var userDTO = mapper.Map<UserDTO>(user);

  • 依賴注入

    使用擴充套件 AutoMapper.Extensions.Microsoft.DependencyInjection 來實現AutoMapper的依賴注入. 本質是註冊一個MapperConfiguration的單例和IMapper的scope例項, 通過程式集掃描新增AutoMapper的相關配置和對映.

    IServiceCollection services = new ServiceCollection();
services.AddAutoMapper();

var provider = services.BuildServiceProvider();
using (var scope = provider.CreateScope())
{
    var mapper = scope.ServiceProvider.GetService<IMapper>();
    var userDTO = mapper.Map<UserDTO>(user);
}

Profile設定

可以使用Profie配置來實現對映關係, 然後通過AddProfile新增.

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>();
    }
}

var config = new MapperConfiguration(cfg => cfg.AddProfile<UserProfile>());

扁平化對映

AutoMapper支援扁平化對映, 它會根據Pascal命名方式分割目標欄位為單個單詞, 可自動對映屬性名+內嵌屬性名. 如下例AutoMapper自動對映UserEntity.Address.City -> UserDTO.AddressCity。

public class UserEntity
{
    public int Id { get; set; }
    public string Name { get; set; }

    public Address Address { get; set; }
}

public class Address
{
    public string City { get; set; }
    public string Country { get; set; }
}

public class UserDTO
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string AddressCity { get; set; }
    public string AddressCountry { get; set; }
}

集合對映

AutoMapper除了可以對映單個物件外，也可以對映集合物件。

CreateMap<UserEntity, UserDTO>();

var userList = new List<UserEntity> {
    new UserEntity { Id = 1, Name="Test1" },
    new UserEntity { Id = 2, Name="Test2" },
};
var dtoList = mapper.Map<List<UserDTO>>(userList);
public class UserEntity
{
    public int Id { get; set; }
    public string Name { get; set; }

    public List<AddressEntity> AddressList { get; set; }
}

public class AddressEntity
{
    public string City { get; set; }
    public string Country { get; set; }
}

public class UserDTO
{
    public int Id { get; set; }
    public string Name { get; set; }

    public List<AddressDTO> AddressList { get; set; }
}

public class AddressDTO
{
    public string City { get; set; }
    public string Country { get; set; }
}

CreateMap<AddressEntity, AddressDTO>();
CreateMap<UserEntity, UserDTO>();

var user = new UserEntity
{
    Id = 1,
    Name = "Test",
    AddressList = new List<AddressEntity>
    {
        new AddressEntity { City = "ShangHai", Country = "China"},
        new AddressEntity { City = "BeiJing", Country = "China"}
    }
};

var userDTO = mapper.Map<UserDTO>(user);

投影

當把一個源值投影到一個不精準匹配源結構的目標值時，使用MapFrom指明成員對映定義。

public class UserEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime BirthDate { get; set; }
}

public class UserDTO
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string BirthYear { get; set; }
    public string BirthMonth { get; set; }
}

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .ForMember(d => d.BirthYear, o => o.MapFrom(s => s.BirthDate.Year))
            .ForMember(d => d.BirthMonth, o => o.MapFrom(s => s.BirthDate.Month));
    }
}

var user = new UserEntity
{
    Id = 1,
    Name = "Test",
    BirthDate = DateTime.Today,
};

var userDTO = mapper.Map<UserDTO>(user);

條件對映

有些情況下，我們將只滿足對映條件的才新增到屬性上.

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .ForMember(d => d.Id, o => o.Condition(s => s.Id > 1));
    }
}

值轉換

AutoMapper可以配置值轉換和空值替換

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .ForMember(d => d.Name, o => o.NullSubstitute("Default Name"))
            .ForMember(d => d.Name, o => o.AddTransform(val => string.Format("Name: {0}", val)));
    }
}

設定轉換前後行為

有時候，在對映發生之前或之後，可能需要執行一些自定義的邏輯。

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .BeforeMap((s, d) => s.BirthDate = s.BirthDate.AddYears(-12))
            .AfterMap((s, d) => d.BirthMonth = "July");
    }
}

配置驗證及設定

配置了對映，但是如何確定是否對映成功或者是否有欄位沒有對映呢？可以使用mapper.ConfigurationProvider.AssertConfigurationIsValid()來驗證是否對映成功。但也可以指定單個欄位不驗證.

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .ForMember(d => d.NickName, o => o.Ignore());
    }
}

反向對映

從6.1.0開始，AutoMapper通過ReverseMap可以實現反向對映。使用ReverseMap, 不用再建立DTO -> Entity的對映, 而且還能保留正向的對映規則。

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .ReverseMap();
    }
}

自定義轉換器

有些情況下目標欄位型別和源欄位型別不一致，可以通過型別轉換器實現對映，型別轉換器有三種實現方式:

void ConvertUsing(Func<TSource, TDestination> mappingFunction);
void ConvertUsing(ITypeConverter<TSource, TDestination> converter);
void ConvertUsing<TTypeConverter>() where TTypeConverter : ITypeConverter<TSource, TDestination>;

自定義解析器

某些情況下，解析規則會很複雜，使用自帶的解析規則無法實現。這時可以自定義解析規則，可以通過以下三種方式使用自定義的解析器：

ResolveUsing<TValueResolver>
ResolveUsing(typeof(CustomValueResolver))
ResolveUsing(aValueResolverInstance)
public class UserEntity
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public class UserDTO
{
    public string Name { get; set; }
}

public class UserNameResolver : IValueResolver<UserEntity, UserDTO, string>
{
    public string Resolve(UserEntity source, UserDTO destination, string destMember, ResolutionContext context)
    {
        if (source != null && !string.IsNullOrEmpty(source.FirstName) && !string.IsNullOrEmpty(source.LastName))
        {
            return string.Format("{0} {1}", source.FirstName, source.LastName);
        }

        return string.Empty;
    }
}

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserEntity, UserDTO>()
            .ForMember(d => d.Name, o => o.ResolveUsing<UserNameResolver>());
    }
}

參考

轉載於:https://www.cnblogs.com/royzshare/p/9951683.html

相關文章