c# - Automapper 5.2 如果在 Base DTO 映射中配置，则忽略 ExplicitExpansion

Question

如果在基本数据传输对象的映射中配置了 ExplicitExpansion() 配置，Automapper 5.2（目前最新）将忽略它。但是如果直接在 Derived DTO 中配置映射，它仍然可以正常工作。我有一对 DTO 类，它们在字段集和映射配置中包含如此多的重复项，我试图将其隔离到公共基础 DTO 类，但是这个问题阻止了我这样做。

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 的未扩展属性时失败。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，我必须将此问题报告给 Automapper 的错误跟踪器？或者它可能是“设计使然”，但为什么呢？（Ivan Stoev 提出了一个可行的修复，但请让我推迟接受答案，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）。

单元测试1.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?");
        }
    }
}

包.config：

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

升级版。Ivan Stoev 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。这与这种方法与 Value 类型（例如 int、int？）的成员崩溃有关。它在下面的第一个单元测试中与崩溃堆栈跟踪一起演示。我将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 - 来自 Ivan Stoev's answer 的修复

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:\01\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。上面更新的问题绝对不能在外面解决，请参阅已接受答案下的评论。这是 AutoMapper 本身的问题。如果您迫不及待地修复更新的问题，您可以使用以下简单（但不是次要）差异制作 AutoMapper 补丁：https ://github.com/moudrick/AutoMapper/commit/65005429609bb568a9373d7f3ae0a535833a1729

score 5 · Accepted Answer

我是否错过了一些代码

你没有错过任何东西。

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？或者它可能是“设计使然”，但为什么呢？

我怀疑这是“设计使然”，很可能是错误或不完整的快速和肮脏的实现。在类的方法的源码里面可以看到，它负责组合基属性和派生属性的配置。“继承的”映射属性当前是：ApplyInheritedPropertyMapPropertyMap

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是否bool明确设置了属性。当然，它可以通过用显式bool?支持字段和默认值逻辑替换自动属性来轻松解决（以及在基类配置中打开它的情况下将其关闭的额外流畅配置方法）。不幸的是，它只能在源代码中完成，所以我建议您将问题报告给他们的问题跟踪器。

直到（如果）他们修复它，我可以建议作为一种解决方法将所有通用代码移动到自定义扩展方法，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。

值类型的第一种情况（带有表达式）失败，因为尝试从中提取的实现MemberInfo仅Expression<Func<T, object>>期望MemberExpression，但在值类型的情况下，它被包装在 aExpression.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一个事实，即从编译时lambda 表达式中提取的基类继承MemberInfo的属性与通过反射或运行时创建的表达式检索到的相同的属性不同，这通过以下测试：

// 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

您绝对需要报告这两个问题。我想说的是，在提供表达式列表时，对于任何值类型的属性，以及在提供名称时，对于任何继承的属性，该功能都会受到影响。

c# - Automapper 5.2 如果在 Base DTO 映射中配置，则忽略 ExplicitExpansion

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