自动映射器映射不使用 After map 时无法工作的条件实体答案

【问题标题】：Auto mapper to map conditional entity which doesn't work without using After map自动映射器映射不使用 After map 时无法工作的条件实体
【发布时间】：2017-07-05 06:23:54
【问题描述】：

您好，我正在使用 Auto mapper 来映射条件实体，如果不使用 After map 将无法工作，但与我不会使用的 After Map 一起工作时效果很好。我想从 Domain.PermanentPlacement 但有条件地映射 InvoiceLineCreditHeader。

以下是映射代码。

 MauritiusMapper.CreateMap<Domain.PermanentPlacement, InvoiceLineCreditHeader>()
                                .ForMember(desc => desc.ApplicantName, o => o.MapFrom(source => source.Candidate.FullName))
                                .ForMember(desc => desc.DatePlaced, o => o.MapFrom(source => source.PlacementDate))
                                .ForMember(desc => desc.ApproveDate, o => o.MapFrom(source => source.LastAuditItem.DateOfAction))
                                .ForMember(desc => desc.CheckedBy, o => o.MapFrom(source => source.StartCheckedBy))
                                .ForMember(desc => desc.Job, o => o.MapFrom(source => source.JobTitle));

        MauritiusMapper.CreateMap<InvoiceLineCreditSearchResult, InvoiceLineCreditData>()
            .ForMember(d => d.InvoiceLineCredits, o => o.MapFrom(s => s.Credits))
            .ForMember(d => d.InvoiceLineCreditHeader, o => o.MapFrom(s => s.InvoiceLine))
            .ForMember(d => d.CreditReasons, o => o.MapFrom(s => s.CreditReasons))
            .ForMember(d => d.CreditStatuses, o => o.MapFrom(s => s.CreditStatuses))
            .ForMember(d => d.InvoiceLineCreditHeader, o => o.MapFrom(s => s.InvoiceLine.TransactionLines.OfType<PermanentPlacementTransactionLine>().FirstOrDefault()?.PermanentPlacement ?? s.ReissuePermanentPlacement))

这会报错

表达式树 lambda 可能不包含空传播运算符。

这是Why can't I use the null propagation operator in lambda expressions?解释的

如果我使用 Aftermap ，它可以正常工作。

        MauritiusMapper.CreateMap<InvoiceLineCreditSearchResult, InvoiceLineCreditData>()
            .ForMember(d => d.InvoiceLineCredits, o => o.MapFrom(s => s.Credits))
            .ForMember(d => d.InvoiceLineCreditHeader, o => o.MapFrom(s => s.InvoiceLine))
            .ForMember(d => d.CreditReasons, o => o.MapFrom(s => s.CreditReasons))
            .ForMember(d => d.CreditStatuses, o => o.MapFrom(s => s.CreditStatuses))
            //.ForMember(d => d.InvoiceLineCreditHeader, o => o.MapFrom(s => s.InvoiceLine.TransactionLines.OfType<PermanentPlacementTransactionLine>().FirstOrDefault()?.PermanentPlacement ?? s.ReissuePermanentPlacement))
            .AfterMap((s, d) =>
            {
                var placement
                = s.InvoiceLine.TransactionLines.OfType<PermanentPlacementTransactionLine>().FirstOrDefault()?.PermanentPlacement ?? s.ReissuePermanentPlacement;
                //  if (placement == null) return;


                d.InvoiceLineCreditHeader.ApplicantId = placement.ApplicantId;
                d.InvoiceLineCreditHeader.ApplicantName = placement.Candidate.FullName;
                d.InvoiceLineCreditHeader.Job = placement.JobTitle;
                d.InvoiceLineCreditHeader.DatePlaced = placement.PlacementDate;
                d.InvoiceLineCreditHeader.PlacedBy = placement.PlacedBy;
                d.InvoiceLineCreditHeader.ApprovedBy = placement.ApprovedBy;
                d.InvoiceLineCreditHeader.ApproveDate = placement.LastAuditItem.DateOfAction;
                d.InvoiceLineCreditHeader.CheckedBy = placement.StartCheckedBy;
                d.InvoiceLineCreditHeader.StartDate = placement.StartDate;
            });

自动映射器中是否有任何方法可以在不使用 AfterMap 的情况下实现这一点？也有条件，但它也使用 linq 表达式。

有什么想法吗？

【问题讨论】：

标签： c# linq lambda automapper

【解决方案1】：

您需要在中找到?. 运算符的替代方法

s.InvoiceLine.TransactionLines.OfType<PermanentPlacementTransactionLine>()
    .FirstOrDefault()?.PermanentPlacement

Select-ing PermanentPlacement 在FirstOrDefault 之前很简单：

s.InvoiceLine.TransactionLines.OfType<PermanentPlacementTransactionLine>()
    .Select(e => e.PermanentPlacement).FirstOrDefault()

【讨论】：

【解决方案2】：

您可以使用所需的逻辑创建一个单独的方法：

private InvoiceLineCreditHeader GetInvoiceLineCreditHeader(InvoiceLineCreditSearchResult result)
{
    // todo: get InvoiceLineCreditHeader conditionally
    InvoiceLineCreditHeader header = new InvoiceLineCreditHeader();
    return header;
}

然后这样称呼它：

.ForMember(d => d.InvoiceLineCreditHeader, o => o.MapFrom(s => GetInvoiceLineCreditHeader(s)))

【讨论】：