如果 Automapper 5.2 在 Base DTO 映射中配置，则忽略 ExplicitExpansion

Question

Automapper 5.2（目前最新）忽略 ExplicitExpansion() 配置，如果它是在基本数据传输对象的映射中配置的。但如果直接在 Derived DTO 中配置映射，它仍然可以正常工作。我有一对 DTO classes，它们在字段集和映射配置中包含如此多的重复，我试图将它隔离到公共基础 DTO class，但这个问题阻止我这样做.

下面是说明这种奇怪行为的代码。有四个测试，其中两个在断言基础 DTO 未扩展属性时失败。如果我将 1-1..1-4 行移动到 2.1，所有测试都会通过。

我是否遗漏了一些代码，或者这是 Automapper 中的错误，我必须将此问题报告给 Automapper 的错误跟踪器？或者可能是 "by design"，但为什么呢？（Ivan Stoev 提出了一个可行的解决方案，但请允许我推迟接受答案，因为我面临的问题并不那么简单，我在下面的更新中添加了更多详细信息）。

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, projectTo.Count()); var first = projectTo.First();
            Assert.IsNotNull(first.Desc); Assert.AreEqual("Descr", 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 已经全面回答了如何解决上面编码的问题。它工作得很好，除非我被迫使用字段名称的字符串数组而不是 MemberExpressions。这与此方法与 Value 类型的成员（如 int、int？）崩溃有关。它在下面的第一个单元测试中与崩溃堆栈跟踪一起演示。我会在另一个问题中询问它，或者更确切地说在错误跟踪器中创建一个问题，因为崩溃绝对是一个错误。

UnitTest2.cs - 根据 Ivan Stoev 的回答修复

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>();
                cfg.CreateMap<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 AutoMapper.QueryableExtensions.Extensions.ProjectTo[TDestination](IQueryable source, Expression`1[] membersToExpand)
//   at AutoMapperIssue.StringPropertyNames.UnitTest2.ProjectAllWithMemberExpression_Exception() in D:\AutoMapperIssue\UnitTest2.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, projectTo.Count()); var first = projectTo.First();
            Assert.IsNull(first.Desc, "Should NOT be expanded.");
            Assert.IsNotNull(first.Name, "Should be expanded. Fails here, why?"); Assert.AreEqual(_iqf.Name, first.Name);

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

UPD2. 上面更新的问题肯定无法在外部修复，请参阅已接受答案下的评论。这是AutoMapper本身的问题。如果您迫不及待地想解决更新后的问题，您可以使用以下简单（但不是次要）差异来制作 AutoMapper 补丁：https://github.com/moudrick/AutoMapper/commit/65005429609bb568a9373d7f3ae0a535833a1729

Answer 1

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?

我怀疑是 "by design"，很可能是错误或不完整的 quick-and-dirty 实现。可以看到PropertyMapclass的ApplyInheritedPropertyMap方法里面的source code，负责结合base属性和derived属性配置。 "inherited" 当前的映射属性是：

CustomExpression
CustomResolver
Condition
PreCondition
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 bool 属性是否被显式设置。当然，它可以很容易地通过用显式 bool? 支持字段和默认值逻辑替换自动属性来解决（以及额外的流畅配置方法来关闭它，以防它在基础 class 配置中打开） .不幸的是，它只能在源代码中完成，所以我建议你向他们的问题跟踪器报告这个问题。

直到（如果）他们修复它，我可以建议将所有通用代码移动到自定义扩展方法作为解决方法，例如

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();
            });
    }
}

并在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：关于附加问题。都是比较严重的AM处理bug，跟配置无关

问题是他们试图使用 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 的实现只期望 MemberExpression，但在值类型的情况下它被包装在 Expression.Convert 里面。

第二种情况（使用属性个名字）失败了，因为他们没有考虑到 MemberInfo 对于 属性从基础 class 从编译时 提取的lambda 表达式与通过反射或运行时创建的表达式检索到的lambda 表达式不同，以下测试证明了这一点：

// 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

您肯定需要报告这两个问题。我想说的是，在提供表达式列表时，任何值类型属性以及提供名称时任何继承属性的功能都会受到影响。

如果 Automapper 5.2 在 Base DTO 映射中配置，则忽略 ExplicitExpansion

Automapper 5.2 ignores ExplicitExpansion if it is configured in Base DTO mapping

c#

inheritance

automapper

automapper-5