c# - 按结果将 Linq 组映射到对象

Question

我有一个作为摘要的类，它将作为 IEnumerable 传递给 MVC 视图。该类看起来像：

public class FixedLineSummary
{
    public long? CustomerId { get; set; }
    public string CustomerName { get; set; }
    public int? NumberOfLines { get; set; }
    public string SiteName { get; set; }
}

从 db 返回的结果包含所有单个条目，因此我使用 linq 来总结这些：

var summary = (from r in result 
              let k = new {r.CustomerId, CustomerName = r.CompanyName, r.SiteName}
              group r by k into t
              select new 
              {
                  t.Key.CustomerId,
                  t.Key.CustomerName,
                  t.Key.SiteName,
                  Lines = t.Sum(r => r.lines)
              });

当我尝试将结果转换为我的对象时，我只是不断收到一个错误：

Instance argument: cannot convert from 'System.Linq.IQueryable<AnonymousType#1>' to 'System.Collections.Generic.IEnumerable<Domain.Entities.FixedLineSummary>'

有没有办法将 linq 查询的结果转换为我的类的枚举？

Answer 1

您应该更改投影以创建您的类，而不是匿名类型：

var summary = from r in result 
              let k = new {r.CustomerId, CustomerName = r.CompanyName, r.SiteName}
              group r by k into t
              select new FixedLineSummary
              {
                  CustomerId = t.Key.CustomerId,
                  CustomerName = t.Key.CustomerName,
                  SiteName = t.Key.SiteName,
                  NumberOfLines = t.Sum(r => r.lines)
              };

Answer 2

您不能将匿名类型转换为，FixedLineSummary因为两者根本不相关（对于编译器）。相反，您需要手动创建类的实例：

IEnumerable<FixedLineSummary> summaries = summary
   .Select(s => new FixedLineSummary
   {
        CustomerId = s.CustomerId,
        CustomerName = s.CustomerName,
        NumberOfLines = s.NumberOfLines,
        SiteName = s.SiteName
   })
   .ToList();