AutoMapper 使用总结

时间 2019-11-12

标签 automapper 使用总结繁體版

原文原文链接

初识AutoMapper

在开始本篇文章以前，先来思考一个问题：一个项目分多层架构，如显示层、业务逻辑层、服务层、数据访问层。层与层访问须要数据载体，也就是类。若是多层通用一个类，一则会暴露出每层的字段，两者会使类字段不少，并且会出现不少冗余字段，这种方式是不可取的；若是每层都使用不一样的类，则层与层调用时，一个字段一个字段的赋值又会很麻烦。针对第二种状况，可使用AutoMapper来帮助咱们实现类字段的赋值及转换。html

AutoMapper是一个对象映射器，它能够将一个一种类型的对象转换为另外一种类型的对象。AutoMapper提供了映射规则及操做方法，使咱们不用过多配置就能够映射两个类。架构

安装AutoMapper

经过Nuget安装AutoMapper，本次使用版本为6.2.2。app

AutoMapper配置

初始化

先建立两个类用于映射：ui

public class ProductEntity
{
	public string Name { get; set; }
	public decimal Amount { get; set; }
}

public class ProductDTO
{
	public string Name { get; set; }
	public decimal Amount { get; set; }
}

Automapper可使用静态类和实例方法来建立映射，下面分别使用这两种方式来实现 ProductEntity -> ProductDTO的映射。spa

使用静态方式

Mapper.Initialize(cfg => cfg.CreateMap<ProductEntity, ProductDTO>());
var productDTO = Mapper.Map<ProductDTO>(productEntity);

使用实例方法

MapperConfiguration configuration = new MapperConfiguration(cfg => cfg.CreateMap<ProductEntity, ProductDTO>());
var mapper = configuration.CreateMapper();
var productDTO = mapper.Map<ProductDTO>(productEntity);

完整的例子：orm

[TestMethod]
public void TestInitialization()
{
	var productEntity = new ProductEntity()
	{
		Name = "Product" + DateTime.Now.Ticks,
		Amount = 10
	};

	Mapper.Initialize(cfg => cfg.CreateMap<ProductEntity, ProductDTO>());
	var productDTO = Mapper.Map<ProductDTO>(productEntity);

	Assert.IsNotNull(productDTO);
	Assert.IsNotNull(productDTO.Name);
	Assert.IsTrue(productDTO.Amount > 0);
}

Profiles设置

除了使用以上两总方式类配置映射关系，也可使用Profie配置来实现映射关系。htm

建立自定义的Profile须要继承Profile类：对象

public class MyProfile : Profile
{
	public MyProfile()
	{
		CreateMap<ProductEntity, ProductDTO>();
		// Other mapping configurations
	}
}

完成例子：blog

[TestMethod]
public void TestProfile()
{
	var productEntity = new ProductEntity()
	{
		Name = "Product" + DateTime.Now.Ticks,
		Amount = 10
	};
	
	var configuration = new MapperConfiguration(cfg => cfg.AddProfile<MyProfile>());
	var productDTO = configuration.CreateMapper().Map<ProductDTO>(productEntity);

	Assert.IsNotNull(productDTO);
	Assert.IsNotNull(productDTO.Name);
	Assert.IsTrue(productDTO.Amount > 0);
}

除了使用AddProfile，也可使用AddProfiles添加多个配置；一样，能够同时使用Mapper和Profile，也能够添加多个配置：继承

var configuration = new MapperConfiguration(cfg =>
{
	cfg.AddProfile<MyProfile>();
	cfg.CreateMap<ProductEntity, ProductDTO>();
});

扁平化映射

AutoMapper先映射名字一致的字段，若是没有，则会尝试使用如下规则来映射：

目标中字段去掉前缀“Get”后的部分
分割目标字段(根据Pascal命名方式)为单个单词

先建立用到的映射类：

public class Product
{
	public Supplier Supplier { get; set; }
	public string Name { get; set; }

	public decimal GetAmount()
	{
		return 10;
	}
}

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

public class ProductDTO
{
	public string SupplierName { get; set; }
	public decimal Amount { get; set; }
}

AutoMapper会自动实现Product.Supplier.Name -> ProductDTO.SupplierName, Product.GetTotal -> ProductDTO.Total的映射。

[TestMethod]
public void TestFalttening()
{
	var supplier = new Supplier()
	{
		Name = "Supplier" + DateTime.Now.Ticks
	};

	var product = new Product()
	{
		Supplier = supplier,
		Name = "Product" + DateTime.Now.Ticks
	};

	Mapper.Initialize(cfg => cfg.CreateMap<Product, ProductDTO>());

	var productDTO = Mapper.Map<ProductDTO>(product);

	Assert.IsNotNull(productDTO);
	Assert.IsNotNull(productDTO.SupplierName);
	Assert.IsTrue(productDTO.Amount > 0);
}

集合验证

AutoMapper除了能够映射单个对象外，也能够映射集合对象。AutoMapper源集合类型支持如下几种：

IEnumerable
IEnumerable<T>
ICollection
ICollection<T>
IList
IList<T>
List<T>
Arrays

简单类型映射：

public class Source
{
	public int Value { get; set; }
}

public class Destination
{
	public int Value { get; set; }
}

[TestMethod]
public void TestCollectionSimple()
{
	Mapper.Initialize(cfg => cfg.CreateMap<Source, Destination>());

	var sources = new[]
	{
		new Source {Value = 1},
		new Source {Value = 2},
		new Source {Value = 3}
	};

	IEnumerable<Destination> ienumerableDest = Mapper.Map<Source[], IEnumerable<Destination>>(sources);
	ICollection<Destination> icollectionDest = Mapper.Map<Source[], ICollection<Destination>>(sources);
	IList<Destination> ilistDest = Mapper.Map<Source[], IList<Destination>>(sources);
	List<Destination> listDest = Mapper.Map<Source[], List<Destination>>(sources);
	Destination[] arrayDest = Mapper.Map<Source[], Destination[]>(sources);
}

复杂对象映射：

public class Order
{
	private IList<OrderLine> _lineItems = new List<OrderLine>();

	public OrderLine[] LineItems { get { return _lineItems.ToArray(); } }

	public void AddLineItem(OrderLine orderLine)
	{
		_lineItems.Add(orderLine);
	}
}

public class OrderLine
{
	public int Quantity { get; set; }
}

public class OrderDTO
{
	public OrderLineDTO[] LineItems { get; set; }
}

public class OrderLineDTO
{
	public int Quantity { get; set; }
}

[TestMethod]
public void TestCollectionNested()
{
	Mapper.Initialize(cfg =>
	{
		cfg.CreateMap<Order, OrderDTO>();
		cfg.CreateMap<OrderLine, OrderLineDTO>();
	});

	var order = new Order();
	order.AddLineItem(new OrderLine {Quantity = 10});
	order.AddLineItem(new OrderLine {Quantity = 20});
	order.AddLineItem(new OrderLine {Quantity = 30});

	var orderDTO = Mapper.Map<OrderDTO>(order);
	Assert.IsNotNull(orderDTO);
	Assert.IsNotNull(orderDTO.LineItems);
	Assert.IsTrue(orderDTO.LineItems.Length > 0);
}

投影及条件映射

投影(指定字段)

除了以上使用的自动映射规则，AutoMapper还能够指定映射方式。下面使用ForMemeber指定字段的映射，将一个时间值拆分映射到日期、时、分：

public class Calendar
{
	public DateTime CalendarDate { get; set; }
	public string Title { get; set; }
}

public class CalendarModel
{
	public DateTime Date { get; set; }
	public int Hour { get; set; }
	public int Minute { get; set; }
	public string Title { get; set; }
}

[TestMethod]
public void TestProjection()
{
	var calendar = new Calendar()
	{
		Title = "2018年日历",
		CalendarDate = new DateTime(2018, 1, 1, 11, 59, 59)
	};

	Mapper.Initialize(cfg => cfg
		.CreateMap<Calendar, CalendarModel>()
		.ForMember(dest => dest.Date, opt => opt.MapFrom(src =>src.CalendarDate.Date))
		.ForMember(dest => dest.Hour, opt => opt.MapFrom(src => src.CalendarDate.Hour))
		.ForMember(dest => dest.Minute, opt => opt.MapFrom(src => src.CalendarDate.Minute)));

	var calendarModel = Mapper.Map<CalendarModel>(calendar);

	Assert.AreEqual(calendarModel.Date.Ticks, new DateTime(2018, 1, 1).Ticks);
	Assert.AreEqual(calendarModel.Hour, 11);
	Assert.AreEqual(calendarModel.Minute, 59);
}

条件映射

有些状况下，咱们会考虑添加映射条件，好比，某个值不符合条件时，不容许映射。针对这种状况可使用ForMember中的Condition：

public class Source
{
	public int Value { get; set; }
}

public class Destination
{
	public uint Value { get; set; }
}


[TestMethod]
public void TestConditionByCondition()
{
	var source = new Source()
	{
		Value = 3
	};

	//若是Source.Value > 0, 则执行映射；不然，映射失败
	Mapper.Initialize(cfg => cfg
		.CreateMap<Source, Destination>()
		.ForMember(dest => dest.Value, opt => opt.Condition(src => src.Value > 0)));

	var destation = Mapper.Map<Destination>(source); //若是不符合条件，则抛出异常

	Assert.IsTrue(destation.Value.Equals(3));
}

若是要映射的类符合必定的规则，并且有不少，针对每一个类都建立一个CreaterMapper会很麻烦。可使用AddConditionalObjectMapper指定对象映射规则，这样就不用每一个映射关系都添加一个CreateMapper。另外，也可使用AddMemberConfiguration指定字段的映射规则，好比字段的先后缀：

public class Product
{
	public string Name { get; set; }
	public int Count { get; set; }
}

public class ProductModel
{
	public string NameModel { get; set; }
	public int CountMod { get; set; }
}

[TestMethod]
public void TestConditionByConfiguration()
{
	var product = new Product()
	{
		Name = "Product" + DateTime.Now.Ticks,
		Count = 10
	};

	var config = new MapperConfiguration(cfg =>
	{
		//对象映射规则: 经过如下配置，能够映射全部”目标对象的名称“等于“源对象名称+Model”的类，而不用单个添加CreateMapper映射
		cfg.AddConditionalObjectMapper().Where((s, d) => d.Name == s.Name + "Model");

		//字段映射规则: 经过如下配置，能够映射“源字段”与“目标字段+Model或Mod”的字段
		cfg.AddMemberConfiguration().AddName<PrePostfixName>(_ => _.AddStrings(p => p.DestinationPostfixes, "Model", "Mod"));
	});

	var mapper = config.CreateMapper();

	var productModel = mapper.Map<ProductModel>(product);

	Assert.IsTrue(productModel.CountMod == 10);
}

须要注意的一点是，添加了以上配置，若是目标对象中有字段没有映射到，则会抛出异常。

值转换

若是配置了值转换，AutoMapper会将修改转换后的值以符合配置的规则。好比，配置目标对象中的值添加符号“@@”：

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

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


[TestMethod]
public void TestValueTransfer()
{
	var source = new Source()
	{
		Name = "Bob"
	};

	Mapper.Initialize(cfg =>
	{
		cfg.CreateMap<Source, Destination>();
		cfg.ValueTransformers.Add<string>(val => string.Format("@{0}@", val));
	});

	var destation = Mapper.Map<Destination>(source);

	Assert.AreEqual("@Bob@", destation.Name);
}

空值替换

若是要映射的值为Null，则可使用NullSubstitute指定Null值的替换值：

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

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


[TestMethod]
public void TestValueTransfer()
{
	var source = new Source()
	{
	};

	Mapper.Initialize(cfg =>
	{
		cfg.CreateMap<Source, Destination>()
		.ForMember(dest => dest.Name, opt => opt.NullSubstitute("其余值"));
	});

	var destation = Mapper.Map<Destination>(source);

	Assert.AreEqual("其余值", destation.Name);
}

配置验证及设置

配置了映射，可是如何肯定是否映射成功或者是否有字段没有映射呢？能够添加Mapper.AssertConfigurationIsValid();来验证是否映射成功。默认状况下，目标对象中的字段都被映射到后，AssertConfigurationIsValid才会返回True。也就是说，源对象必须包含全部目标对象，这样在大多数状况下不是咱们想要的，咱们可使用下面的方法来指定验证规则：

指定单个字段不验证
指定整个Map验证规则

public class Product
{
    public string Name { get; set; }
    public int Amount { get; set; }
}

public class ProductModel
{
    public string Name { get; set; }
    public int Amount { get; set; }
    public string ViewName { get; set; }
}

public class ProductDTO
{
    public string Name { get; set; }
    public int Amount { get; set; }
    public string ViewName { get; set; }
}

[TestMethod]
public void TestValidation()
{
    var product = new Product()
    {
        Name = "Product" + DateTime.Now.Ticks,
        Amount = 10
    };

    Mapper.Initialize(cfg =>
    {
        //1. 指定字段映射方式
        cfg.CreateMap<Product, ProductModel>()
            .ForMember(dest => dest.ViewName, opt => opt.Ignore()); //若是不添加此设置，会抛出异常

        //2. 指定整个对象映射方式
        //MemberList: 
        //  Source: 检查源对象全部字段映射成功
        //  Destination：检查目标对象全部字段映射成功
        //  None: 跳过验证
        cfg.CreateMap<Product, ProductDTO>(MemberList.Source);
    });

    var productModel = Mapper.Map<ProductModel>(product);
    var productDTO = Mapper.Map<ProductDTO>(product);

    //验证映射是否成功
    Mapper.AssertConfigurationIsValid();
}

设置转换先后行为

有的时候你可能会在建立映射先后对数据作一些处理，AutoMapper就提供了这种方式：

public class Source
{
    public string Name { get; set; }
    public int Value { get; set; }
}

public class Destination
{
    public string Name { get; set; }
    public int Value { get; set; }
}

[TestMethod]
public void TestBeforeOrAfter()
{
    var source = new Source()
    {
        Name = "Product" + DateTime.Now.Ticks,
    };

    Mapper.Initialize(cfg =>
    {
        cfg.CreateMap<Source, Destination>()
            .BeforeMap((src, dest) => src.Value = src.Value + 10)
            .AfterMap((src, dest) => dest.Name = "Pobin");
    });

    var productModel = Mapper.Map<Destination>(source);

    Assert.AreEqual("Pobin", productModel.Name);
}

反向映射

从6.1.0开始，AutoMapper经过调用Reverse能够实现反向映射。反向映射根据初始化时建立的正向映射规则来作反向映射：

public class Order
{
	public decimal Total { get; set; }
	public Customer Customer { get; set; }
}

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

public class OrderDTO
{
	public decimal Total { get; set; }
	public string CustomerName { get; set; }
}

[TestMethod]
public void TestReverseMapping()
{
	var customer = new Customer
	{
		Name = "Tom"
	};

	var order = new Order
	{
		Customer = customer,
		Total = 20
	};

	Mapper.Initialize(cfg => {
		cfg.CreateMap<Order, OrderDTO>()
			.ForMember(dest => dest.CustomerName, opt => opt.MapFrom(src => src.Customer.Name)) //正向映射规则
			.ReverseMap(); //设置反向映射
	});

	//正向映射
	var orderDTO = Mapper.Map<OrderDTO>(order);

	//反向映射：使用ReverseMap,不用再建立OrderDTO -> Order的映射，并且还能保留正向的映射规则
	var orderConverted = Mapper.Map<Order>(orderDTO);

	Assert.IsNotNull(orderConverted.Customer);
	Assert.AreEqual("Tom", orderConverted.Customer.Name);
}

若是反向映射中不想使用原先的映射规则，也能够取消掉：

Mapper.Initialize(cfg => {
	cfg.CreateMap<Order, OrderDTO>()
		.ForMember(dest => dest.CustomerName, opt => opt.MapFrom(src => src.Customer.Name)) //正向映射规则
		.ReverseMap()
		.ForPath(src => src.Customer.Name, opt => opt.Ignore()); //设置反向映射
});

自定义转换器

有些状况下目标字段类型和源字段类型不一致，能够经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>;

下面经过一个例子来演示下以上三种类型转换器的使用方式：

namespace AutoMapperSummary
{
    [TestClass]
    public class CustomerTypeConvert
    {
        public class Source
        {
            public string Value1 { get; set; }
            public string Value2 { get; set; }
            public string Value3 { get; set; }
        }

        public class Destination
        {
            public int Value1 { get; set; }
            public DateTime Value2 { get; set; }
            public Type Value3 { get; set; }
        }

        public class DateTimeTypeConverter : ITypeConverter<string, DateTime>
        {
            public DateTime Convert(string source, DateTime destination, ResolutionContext context)
            {
                return System.Convert.ToDateTime(source);
            }
        }

        public class TypeTypeConverter : ITypeConverter<string, Type>
        {
            public Type Convert(string source, Type destination, ResolutionContext context)
            {
                return Assembly.GetExecutingAssembly().GetType(source);
            }
        }

        [TestMethod]
        public void TestTypeConvert()
        {
            var config = new MapperConfiguration(cfg =>
            {
                cfg.CreateMap<string, int>().ConvertUsing((string s) => Convert.ToInt32(s));
                cfg.CreateMap<string, DateTime>().ConvertUsing(new DateTimeTypeConverter());
                cfg.CreateMap<string, Type>().ConvertUsing<TypeTypeConverter>();
                cfg.CreateMap<Source, Destination>();
            });

            config.AssertConfigurationIsValid(); //验证映射是否成功

            var source = new Source
            {
                Value1 = "20",
                Value2 = "2018/1/1",
                Value3 = "AutoMapperSummary.CustomerTypeConvert+Destination"
            };

            var mapper = config.CreateMapper();
            var destination = mapper.Map<Source, Destination>(source);

            Assert.AreEqual(typeof(Destination), destination.Value3);
        }
    }
}

自定义解析器

使用AutoMapper的自带解析规则，咱们能够很方便的实现对象的映射。好比：源/目标字段名称一致，“Get/get + 源字段“与"目标字段"一致等。除了这些简单的映射，还可使用ForMember指定字段映射。可是，某些状况下，解析规则会很复杂，使用自带的解析规则没法实现。这时能够自定义解析规则，能够经过如下三种方式使用自定义的解析器：

ResolveUsing<TValueResolver>
ResolveUsing(typeof(CustomValueResolver))
ResolveUsing(aValueResolverInstance)

下面经过一个例子来演示如何使用自定义解析器：

public class Source
{
	public string FirstName { get; set; }
	public string LastName { get; set; }
}

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

/// <summary>
/// 自定义解析器: 组合姓名
/// </summary>
public class CustomResolver : IValueResolver<Source, Destination, string>
{
	public string Resolve(Source source, Destination 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;
	}
}

[TestMethod]
public void TestResolver()
{
	Mapper.Initialize(cfg =>
		cfg.CreateMap<Source, Destination>()
			.ForMember(dest => dest.Name, opt => opt.ResolveUsing<CustomResolver>()));

	Mapper.AssertConfigurationIsValid();

	var source = new Source
	{
		FirstName = "Michael",
		LastName = "Jackson"
	};

	var destination = Mapper.Map<Source, Destination>(source);
	Assert.AreEqual("Michael Jackson", destination.Name);
}

AutoMapper封装

AutoMapper功能很强大，自定义配置支持也很是好，可是真正项目中使用时却不多用到这么多功能，并且通常都会对AutoMapper进一步封装使用。一方面使用起来方面，另一方面也可使代码统一。下面的只是作一个简单的封装，还须要结合实际项目使用：

/// <summary>
    /// AutoMapper帮助类
    /// </summary>
    public class AutoMapperManager
    {
        private static readonly MapperConfigurationExpression MapperConfiguration = new MapperConfigurationExpression();

        static AutoMapperManager()
        {
        }

        private AutoMapperManager()
        {
            AutoMapper.Mapper.Initialize(MapperConfiguration);
        }

        public static AutoMapperManager Instance { get; } = new AutoMapperManager();

        /// <summary>
        /// 添加映射关系
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        public void AddMap<TSource, TDestination>() where TSource : class, new() where TDestination : class, new()
        {
            MapperConfiguration.CreateMap<TSource, TDestination>();
        }

        /// <summary>
        /// 获取映射值
        /// </summary>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public TDestination Map<TDestination>(object source) where TDestination : class, new()
        {
            if (source == null)
            {
                return default(TDestination);
            }

            return Mapper.Map<TDestination>(source);
        }

        /// <summary>
        /// 获取集合映射值
        /// </summary>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public IEnumerable<TDestination> Map<TDestination>(IEnumerable source) where TDestination : class, new()
        {
            if (source == null)
            {
                return default(IEnumerable<TDestination>);
            }

            return Mapper.Map<IEnumerable<TDestination>>(source);
        }

        /// <summary>
        /// 获取映射值
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public TDestination Map<TSource, TDestination>(TSource source) where TSource : class, new () where TDestination : class, new()
        {
            if (source == null)
            {
                return default(TDestination);
            }

            return Mapper.Map<TSource, TDestination>(source);
        }

        /// <summary>
        /// 获取集合映射值
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public IEnumerable<TDestination> Map<TSource, TDestination>(IEnumerable<TSource> source) where TSource : class, new() where TDestination : class, new()
        {
            if (source == null)
            {
                return default(IEnumerable<TDestination>);
            }

            return Mapper.Map<IEnumerable<TSource>, IEnumerable<TDestination>>(source);
        }

        /// <summary>
        /// 读取DataReader内容
        /// </summary>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="reader"></param>
        /// <returns></returns>
        public IEnumerable<TDestination> Map<TDestination>(IDataReader reader)
        {
            if (reader == null)
            {
                return new List<TDestination>();
            }

            var result = Mapper.Map<IEnumerable<TDestination>>(reader);

            if (!reader.IsClosed)
            {
                reader.Close();
            }
            
            return result;
        }
    }

总结

本篇文章列举了AutoMapper的基本使用方式，更多的使用能够参考官方文档：http://automapper.readthedocs.io/en/latest/index.html