AutoMapper 简介

AutoMapper是一个对象映射器，它可以将一种类型的对象转换为另一种类型的对象。

它提供了映射规则及操作方法，使我们不用过多配置就可以映射两个类, 可以帮我们免于编写无聊的映射代码. 在代码层与层之间隔离模型model上非常有用.

AutoMapper 使用

初始化

创建两个简单的类用于测试:

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可以使用静态类和实例方法来创建映射.

静态类方式

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

实例方式

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

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

依赖注入

使用扩展 AutoMapper.Extensions.Microsoft.DependencyInjection 来实现AutoMapper的依赖注入. 本质是注册一个MapperConfiguration的单例和IMapper的scope实例, 通过程序集扫描添加AutoMapper的相关配置和映射.

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设置

可以使用Profie配置来实现映射关系, 然后通过AddProfile添加.

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

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

扁平化映射

AutoMapper支持扁平化映射, 它会根据Pascal命名方式分割目标字段为单个单词, 可自动映射属性名+内嵌属性名. 如下例AutoMapper自动映射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; }
}

集合映射

AutoMapper除了可以映射单个对象外，也可以映射集合对象。

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

当把一个源值投影到一个不精准匹配源结构的目标值时，使用MapFrom指明成员映射定义。

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);

条件映射

有些情况下，我们将只满足映射条件的才添加到属性上.

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

值转换

AutoMapper可以配置值转换和空值替换

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)));
    }
}

设置转换前后行为

有时候，在映射发生之前或之后，可能需要执行一些自定义的逻辑。

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

配置验证及设置

配置了映射，但是如何确定是否映射成功或者是否有字段没有映射呢？可以使用mapper.ConfigurationProvider.AssertConfigurationIsValid()来验证是否映射成功。但也可以指定单个字段不验证.

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

反向映射

从6.1.0开始，AutoMapper通过ReverseMap可以实现反向映射。使用ReverseMap, 不用再创建DTO -> Entity的映射, 而且还能保留正向的映射规则。

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

自定义转换器

有些情况下目标字段类型和源字段类型不一致，可以通过类型转换器实现映射，类型转换器有三种实现方式:

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

自定义解析器

某些情况下，解析规则会很复杂，使用自带的解析规则无法实现。这时可以自定义解析规则，可以通过以下三种方式使用自定义的解析器：

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>());
    }
}

来源：oschina

链接：https://my.oschina.net/it110/blog/4358829

标签

ASP.NET Core

automapper

entity

asp.net core之AutoMapper