c# – 如果在Base DTO映射中配置了ExplicitExpansion,Automapper

发布时间：2020-12-15 07:42:24 所属栏目：百科来源：网络整理

导读：Automapper 5.2(当前最新)如果在Base Data Transfer Object的映射中配置,则忽略ExplicitExpansion()配置.但是,如果直接在Derived DTO中配置了映射,它仍然可以正常工作.我有一对DTO类,它们在字段集和映射配置中包含很多重复,我试图将它隔离到公共基础DTO类,但

Automapper 5.2(当前最新)如果在Base Data Transfer Object的映射中配置,则忽略ExplicitExpansion()配置.但是,如果直接在Derived DTO中配置了映射,它仍然可以正常工作.我有一对DTO类,它们在字段集和映射配置中包含很多重复,我试图将它隔离到公共基础DTO类,但是这个问题阻止了我这样做.

下面的代码说明了这种奇怪的行为.有四个测试,其中两个未能断言未扩展基础DTO的属性.如果我将1-1..1-4行移动到2.1,则所有测试都通过.

我是否错过了一些代码或者这是Automapper中的错误,我必须向Automapper的错误跟踪器报告此问题？或者它可能是“按设计”,但为什么呢？ (Ivan Stoev提出了一个有效的解决方案,但请允许我推迟接受答案,因为我面临的问题不是那么简单,我在下面的更新中添加了更多细节).

的UnitTest1.cs：

using System.Collections.Generic;
using System.Linq;
using AutoMapper;
using AutoMapper.QueryableExtensions;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace AutoMapperIssue 
{
    public class Source { public string Name; public string Desc; }
    public class DtoBase              { public string Name { get; set; } }
    public class DtoDerived : DtoBase { public string Desc { get; set; } }
    [TestClass] public class UnitTest1
    {
        [AssemblyInitialize] public static void AssemblyInit(TestContext context)
        {
            Mapper.Initialize(cfg =>
            {
                cfg.CreateMap<Source,DtoBase>()
                    .ForMember(dto => dto.Name,conf => { // line 1-1
                        conf.MapFrom(src => src.Name);    // line 1-2
                        conf.ExplicitExpansion();         // line 1-3
                    })                                    // line 1-4
                    .Include<Source,DtoDerived>();
                cfg.CreateMap<Source,DtoDerived>()
                    // place 2.1
                    .ForMember(dto => dto.Desc,conf => {
                        conf.MapFrom(src => src.Desc);
                        conf.ExplicitExpansion();
                    });
            });
            Mapper.Configuration.CompileMappings();
            Mapper.AssertConfigurationIsValid();
        }

        private readonly IQueryable<Source> _iq = new List<Source> {
            new Source() { Name = "Name1",Desc = "Descr",},} .AsQueryable();

        [TestMethod] public void ProjectAll_Success() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(_ => _.Name,_ => _.Desc);
            Assert.AreEqual(1,projectTo.Count()); var first = projectTo.First();
            Assert.IsNotNull(first.Desc); Assert.AreEqual("Descr",first.Desc);
            Assert.IsNotNull(first.Name); Assert.AreEqual("Name1",first.Name);
        }
        [TestMethod] public void SkipDerived_Success() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(_ => _.Name);
            Assert.AreEqual(1,projectTo.Count()); var first = projectTo.First();
            Assert.IsNotNull(first.Name); Assert.AreEqual("Name1",first.Name);
            Assert.IsNull(first.Desc,"Should not be expanded.");
        }
        [TestMethod] public void SkipBase_Fail() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(_ => _.Desc);
            Assert.AreEqual(1,first.Desc);
            Assert.IsNull(first.Name,"Should not be expanded. Fails here. Why?");
        }
        [TestMethod] public void SkipAll_Fail() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>();
            Assert.AreEqual(1,projectTo.Count()); var first = projectTo.First();
            Assert.IsNull(first.Desc,"Should not be expanded.");
            Assert.IsNull(first.Name,"Should not be expanded. Fails here. Why?");
        }
    }
}

packages.config：

<package id="AutoMapper" version="5.2.0" targetFramework="net452" />

UPD. Ivan Stoev全面回答了如何解决上面编码的问题.除非我被迫使用字段名称的字符串数组而不是MemberExpressions,否则它的效果非常好.这与这种方法与Value类型的成员(例如int,int？)崩溃有关.在下面的第一个单元测试中演示了崩溃堆栈跟踪.我会在另一个问题中询问它,或者更确切地说是在bug跟踪器中创建一个问题,因为崩溃肯定是一个bug.

UnitTest2.cs – 修复了Ivan Stoev的回答

using System;
using System.Collections.Generic;
using System.Linq;
using AutoMapper;
using AutoMapper.QueryableExtensions;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace AutoMapperIssue.StringPropertyNames 
{   /* int? (or any ValueType) instead of string - .ProjectTo<> crashes on using MemberExpressions in projction */
    using NameSourceType = Nullable<int> /* String */; using NameDtoType = Nullable<int> /* String */;
    using DescSourceType = Nullable<int> /* String */; using DescDtoType = Nullable<int> /* String*/;

    public class Source
    {   
        public NameSourceType Name { get; set; }
        public DescSourceType Desc { get; set; }
    }

    public class DtoBase              { public NameDtoType Name { get; set; } }
    public class DtoDerived : DtoBase { public DescDtoType Desc { get; set; } }

    static class MyMappers
    {
        public static IMappingExpression<TSource,TDestination> Configure<TSource,TDestination>(this IMappingExpression<TSource,TDestination> target)
            where TSource : Source
            where TDestination : DtoBase
        {
            return target.ForMember(dto => dto.Name,conf =>
                {
                    conf.MapFrom(src => src.Name);
                    conf.ExplicitExpansion();
                });
        }
    }

    [TestClass] public class UnitTest2
    {
        [ClassInitialize] public static void ClassInit(TestContext context)
        {
            Mapper.Initialize(cfg =>
            {
                cfg.CreateMap<Source,DtoBase>()
                    .Configure()
                    .Include<Source,DtoDerived>()
                    .Configure()
                    .ForMember(dto => dto.Desc,conf => {
                        conf.MapFrom(src => src.Desc);
                        conf.ExplicitExpansion();
                    })
                ;
            });
            Mapper.Configuration.CompileMappings();
            Mapper.AssertConfigurationIsValid();
        }

        private static readonly IQueryable<Source> _iq = new List<Source> {
            new Source() { Name = -25 /* "Name1" */,Desc = -12 /* "Descr" */,} .AsQueryable();

        private static readonly Source _iqf = _iq.First();

        [TestMethod] public void ProjectAllWithMemberExpression_Exception() 
        {
            _iq.ProjectTo<DtoDerived>(_ => _.Name,_ => _.Desc); // Exception here,no way to use Expressions with current release
//Test method AutoMapperIssue.StringPropertyNames.UnitTest2.ProjectAllWithMemberExpression_Exception threw exception: 
//System.NullReferenceException: Object reference not set to an instance of an object.
//
//    at System.Linq.Enumerable.<SelectManyIterator>d__16`2.MoveNext()
//   at System.Linq.Enumerable.<DistinctIterator>d__63`1.MoveNext()
//   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
//   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
//   at AutoMapper.QueryableExtensions.ProjectionExpression.To[TResult](IDictionary`2 parameters,IEnumerable`1 memberPathsToExpand)
//   at AutoMapper.QueryableExtensions.ProjectionExpression.To[TResult](Object parameters,Expression`1[] membersToExpand)
//   at AutoMapper.QueryableExtensions.Extensions.ProjectTo[TDestination](IQueryable source,IConfigurationProvider configuration,Object parameters,Expression`1[] membersToExpand)
//   at AutoMapperIssue.StringPropertyNames.UnitTest2.ProjectAllWithMemberExpression_Exception() in D:1AutoMapperIssueUnitTest2.cs:line 84
        }
#pragma warning disable 649
        private DtoDerived d;
#pragma warning restore 649
        [TestMethod] public void ProjectAll_Fail() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(null,new string[] { nameof(d.Name),nameof(d.Desc) } /* _ => _.Name,_ => _.Desc */);
            Assert.AreEqual(1,projectTo.Count()); var first = projectTo.First();
            Assert.IsNotNull(first.Desc,"Should be expanded.");                  Assert.AreEqual(_iqf.Desc,first.Desc);
            Assert.IsNotNull(first.Name,"Should be expanded. Fails here,why?"); Assert.AreEqual(_iqf.Name,first.Name);
        }
        [TestMethod] public void BaSEOnly_Fail() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(null,new string[] { nameof(d.Name) } /* _ => _.Name */);
            Assert.AreEqual(1,"Should NOT be expanded.");
            Assert.IsNotNull(first.Name,first.Name);

        }
        [TestMethod] public void DerivedOnly_Success() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(null,new string[] { nameof(d.Desc) } /* _ => _.Desc */);
            Assert.AreEqual(1,"Should be expanded."); Assert.AreEqual(_iqf.Desc,"Should NOT be expanded.");
        }
        [TestMethod] public void SkipAll_Success() 
        {
            var projectTo = _iq.ProjectTo<DtoDerived>(null,new string[] { });
            Assert.AreEqual(1,"Should NOT be expanded.");
            Assert.IsNull(first.Name,"Should NOT be expanded.");
        }
    }
}

UPD2.上面更新的问题肯定无法在外面修复,请参阅接受的答案下的评论.这是AutoMapper本身的问题.如果您迫不及待地想要修复更新的问题,可以使用以下简单(但不是次要)差异来制作AutoMapper补丁：https://github.com/moudrick/AutoMapper/commit/65005429609bb568a9373d7f3ae0a535833a1729

解决方法

Have I missed some piece of code

你没有错过任何东西.

or is this a bug in Automapper and I have to report this issue to Automapper’s bug tracker? Or is it probably “by design”,but why?

我怀疑这是“按设计”,很可能是错误或不完整的快速和脏实施.可以在PropertyMap类的ApplyInheritedPropertyMap方法的source code内部看到,该方法负责组合基本属性和派生属性配置. “继承的”映射属性目前是：

> CustomExpression
> CustomResolver
>条件
>前提条件
> NullSubstitute
> MappingOrder
> ValueResolverConfig

而以下(基本上所有bool类型)属性(包括有问题的属性)不是：

> AllowNull
> UseDestinationValue
> ExplicitExpansion

IMO的问题是当前的实现无法确定是否明确设置了bool属性.当然,通过用显式bool替换auto属性可以很容易地解决它？支持字段和默认值逻辑(以及其他流畅的配置方法,以便在基类配置中打开它时将其关闭).不幸的是,它只能在源代码中完成,因此我建议您将问题报告给他们的问题跟踪器.

直到(以及如果)他们修复它,我可以建议将所有常用代码移动到自定义扩展方法,如

static class MyMappers
{
    public static IMappingExpression<TSource,TDestination> target)
        where TSource : Source
        where TDestination : DtoBase
    {
        return target
            .ForMember(dto => dto.Name,conf =>
            {
                conf.MapFrom(src => src.Name);
                conf.ExplicitExpansion();
            });
    }
}

并从主配置代码中使用它们：

Mapper.Initialize(cfg =>
{
    cfg.CreateMap<Source,DtoBase>()
        .Configure();

    cfg.CreateMap<Source,DtoDerived>()
        .Configure()
        .ForMember(dto => dto.Desc,conf => {
            conf.MapFrom(src => src.Desc);
            conf.ExplicitExpansion();
        });
});

编辑：关于其他问题.两者都是更严重的AM处理错误,与配置无关.

问题是他们尝试使用MemberInfo实例比较来过滤投影.

第一种情况(带表达式)对于值类型失败,因为尝试从Expression< Func< T,object>>中提取MemberInfo的实现我只期待MemberExpression,但是在值类型的情况下,它包含在Expression.Convert中.

第二种情况(带有属性名称)失败,因为他们没有考虑这样的事实：从编译时lambda表达式中提取的基类继承的属性的MemberInfo与反射或运行时创建的表达式检索的属性不同,这与以下测试：

// From reflection
var nameA = typeof(DtoDerived).GetMember(nameof(DtoDerived.Name)).Single();
// Same as
//var nameA = typeof(DtoDerived).GetProperty(nameof(DtoDerived.Name));

// From compile time expression
Expression<Func<DtoDerived,NameDtoType>> compileTimeExpr = _ => _.Name;
var nameB = ((MemberExpression)compileTimeExpr.Body).Member;

// From runtime expression
var runTimeExpr = Expression.PropertyOrField(Expression.Parameter(typeof(DtoDerived)),nameof(DtoDerived.Name));
var nameC = runTimeExpr.Member;

Assert.AreEqual(nameA,nameC); // Success
Assert.AreEqual(nameA,nameB); // Fail

你肯定需要报告这两个问题.我会说,在提供表达式列表时,任何值类型属性都会泄露该功能,并且在提供名称时,任何继承的属性都会泄露.

（编辑：李大同）

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