AutoMapper 使用总结1

初识AutoMapper

在开始本篇文章之前,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。层与层访问需要数据载体,也就是类。如果多层通用一个类,一则会暴露出每层的字段,二者会使类字段很多,而且会出现很多冗余字段,这种方式是不可取的;如果每层都使用不同的类,则层与层调用时,一个字段一个字段的赋值又会很麻烦。针对第二种情况,可以使用AutoMapper来帮助我们实现类字段的赋值及转换。

AutoMapper是一个对象映射器,它可以将一个一种类型的对象转换为另一种类型的对象。AutoMapper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。

安装AutoMapper

通过Nuget安装AutoMapper,本次使用版本为6.2.2。

AutoMapper配置

初始化

先创建两个类用于映射:

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public class ProductEntity
{
    public string Name { getset; }
    public decimal Amount { getset; }
}
 
public class ProductDTO
{
    public string Name { getset; }
    public decimal Amount { getset; }
}

Automapper可以使用静态类和实例方法来创建映射,下面分别使用这两种方式来实现 ProductEntity -> ProductDTO的映射。

  • 使用静态方式
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Mapper.Initialize(cfg => cfg.CreateMap<ProductEntity, ProductDTO>());
var productDTO = Mapper.Map<ProductDTO>(productEntity);
  • 使用实例方法
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MapperConfiguration configuration = new MapperConfiguration(cfg => cfg.CreateMap<ProductEntity, ProductDTO>());
var mapper = configuration.CreateMapper();
var productDTO = mapper.Map<ProductDTO>(productEntity);

完整的例子:

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[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,也可以使用Profie配置来实现映射关系。

创建自定义的Profile需要继承Profile类:

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

完成例子:

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[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,也可以使用AddProfiles添加多个配置;同样,可以同时使用Mapper和Profile,也可以添加多个配置:

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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,如果没有,则会尝试使用以下规则来映射:

  • 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

先创建用到的映射类:

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public class Product
{
    public Supplier Supplier { getset; }
    public string Name { getset; }
 
    public decimal GetAmount()
    {
        return 10;
    }
}
 
public class Supplier
{
    public string Name { getset; }
}
 
public class ProductDTO
{
    public string SupplierName { getset; }
    public decimal Amount { getset; }
}

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

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[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除了可以映射单个对象外,也可以映射集合对象。AutoMapper源集合类型支持以下几种:

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

简单类型映射:

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public class Source
{
    public int Value { getset; }
}
 
public class Destination
{
    public int Value { getset; }
}
 
[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:

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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 { getset; }
}
 
public class OrderDTO
{
    public OrderLineDTO[] LineItems { getset; }
}
 
public class OrderLineDTO
{
    public int Quantity { getset; }
}
 
[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还可以指定映射方式。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:

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public class Calendar
{
    public DateTime CalendarDate { getset; }
    public string Title { getset; }
}
 
public class CalendarModel
{
    public DateTime Date { getset; }
    public int Hour { getset; }
    public int Minute { getset; }
    public string Title { getset; }
}
 
[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

 有些情况下,我们会考虑添加映射条件,比如,某个值不符合条件时,不允许映射。针对这种情况可以使用ForMember中的Condition:

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public class Source
{
    public int Value { getset; }
}
 
public class Destination
{
    public uint Value { getset; }
}
 
 
[TestMethod]
public void TestConditionByCondition()
{
    var source = new Source()
    {
        Value = 3
    };
 
    //如果Source.Value > 0, 则执行映射;否则,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); //如果不符合条件,则抛出异常
 
    Assert.IsTrue(destation.Value.Equals(3));
}

如果要映射的类符合一定的规则,而且有很多,针对每个类都创建一个CreaterMapper会很麻烦。可以使用AddConditionalObjectMapper指定对象映射规则,这样就不用每个映射关系都添加一个CreateMapper。另外,也可以使用AddMemberConfiguration指定字段的映射规则,比如字段的前后缀:

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public class Product
{
    public string Name { getset; }
    public int Count { getset; }
}
 
public class ProductModel
{
    public string NameModel { getset; }
    public int CountMod { getset; }
}
 
[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: 通过以下配置,可以映射所有”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: 通过以下配置,可以映射“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);
}

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

值转换

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

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public class Source
{
    public string Name { getset; }
}
 
public class Destination
{
    public string Name { getset; }
}
 
 
[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

如果要映射的值为Null,则可以使用NullSubstitute指定Null值的替换值:

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public class Source
{
    public string Name { getset; }
}
 
public class Destination
{
    public string Name { getset; }
}
 
 
[TestMethod]
public void TestValueTransfer()
{
    var source = new Source()
    {
    };
 
    Mapper.Initialize(cfg =>
    {
        cfg.CreateMap<Source, Destination>()
        .ForMember(dest => dest.Name, opt => opt.NullSubstitute("其他值"));
    });
 
    var destation = Mapper.Map<Destination>(source);
 
    Assert.AreEqual("其他值", destation.Name);
}

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?可以添加Mapper.AssertConfigurationIsValid();来验证是否映射成功。默认情况下,目标对象中的字段都被映射到后,AssertConfigurationIsValid才会返回True。也就是说,源对象必须包含所有目标对象,这样在大多数情况下不是我们想要的,我们可以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
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public class Product
{
    public string Name { getset; }
    public int Amount { getset; }
}
 
public class ProductModel
{
    public string Name { getset; }
    public int Amount { getset; }
    public string ViewName { getset; }
}
 
public class ProductDTO
{
    public string Name { getset; }
    public int Amount { getset; }
    public string ViewName { getset; }
}
 
[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()); //如果不添加此设置,会抛出异常
 
        //2. 指定整个对象映射方式
        //MemberList:
        //  Source: 检查源对象所有字段映射成功
        //  Destination:检查目标对象所有字段映射成功
        //  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();
}

设置转换前后行为

有的时候你可能会在创建映射前后对数据做一些处理,AutoMapper就提供了这种方式:

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public class Source
{
    public string Name { getset; }
    public int Value { getset; }
}
 
public class Destination
{
    public string Name { getset; }
    public int Value { getset; }
}
 
[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通过调用Reverse可以实现反向映射。反向映射根据初始化时创建的正向映射规则来做反向映射:

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public class Order
{
    public decimal Total { getset; }
    public Customer Customer { getset; }
}
 
public class Customer
{
    public string Name { getset; }
}
 
public class OrderDTO
{
    public decimal Total { getset; }
    public string CustomerName { getset; }
}
 
[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,不用再创建OrderDTO -> Order的映射,而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);
}

如果反向映射中不想使用原先的映射规则,也可以取消掉:

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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:

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

下面通过一个例子来演示下以上三种类型转换器的使用方式:

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namespace AutoMapperSummary
{
    [TestClass]
    public class CustomerTypeConvert
    {
        public class Source
        {
            public string Value1 { getset; }
            public string Value2 { getset; }
            public string Value3 { getset; }
        }
 
        public class Destination
        {
            public int Value1 { getset; }
            public DateTime Value2 { getset; }
            public Type Value3 { getset; }
        }
 
        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<stringint>().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,我们可以很方便的实现对象的映射。比如: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,还可以使用ForMember指定字段映射。但是,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:

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

下面通过一个例子来演示如何使用自定义解析器:

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public class Source
{
    public string FirstName { getset; }
    public string LastName { getset; }
}
 
public class Destination
{
    public string Name { getset; }
}
 
/// <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,自定义配置支持也非常好,但是真正项目中使用时却很少用到这么多功能,而且一般都会对AutoMapper进一步封装使用。一方面使用起来方面,另外一方面也可以使代码统一。下面的只是做一个简单的封装,还需要结合实际项目使用:

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/// <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 : classnew() where TDestination : classnew()
        {
            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 : classnew()
        {
            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 : classnew()
        {
            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 : classnew () where TDestination : classnew()
        {
            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 : classnew() where TDestination : classnew()
        {
            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,更多的使用可以参考官方文档:http://automapper.readthedocs.io/en/latest/index.html

posted @ 2018-08-23 18:01  BK小鬼  阅读(827)  评论(0编辑  收藏  举报