c# - spring.net 表达式求值器-spel-list 迭代

Question

我正在尝试在 SpEL 中执行以下行，但它不起作用：

FileAttachments.?{DownloadedPath.Contains('CMA')}.count()>0

where是属性为FileAttachments的类对象的列表。FileAttachmentDownloadedPath

基本上我正在尝试检查是否有任何属性包含FileAttachment" CMA"。DownloadedPath

但它返回错误：

选择只能用于实现 IEnumerable 的类型的实例。

Answer 1

我创建了一个简单的原型，因为我认为您的表达式应该有效并且确实有效：

using System.Collections.Generic;
using System.Diagnostics;
using Spring.Expressions;

namespace StackOverflow10159903
{
  internal class Program
  {
    private static void Main(string[] args)
    {
      var attachmentContainer = new FileAttachmentsContainer();
      attachmentContainer.AddAttachment(new FileAttachment {DownloadedPath = "CMA"});

      var attachments = new List<FileAttachment>();
      attachments.Add(new FileAttachment {DownloadedPath = "CMA"});

      var valueFromList =
        ExpressionEvaluator.GetValue(attachments, "?{DownloadedPath.Contains('CMA')}.count()>0") 
        as bool?;

      var valueFromContainer =
        ExpressionEvaluator.GetValue(attachmentContainer, "FileAttachments?{DownloadedPath.Contains('CMA')}.count()>0")
        as bool?;

      Debug.Assert(valueFromList == true);
      Debug.Assert(valueFromContainer == true);
    }
  }

  public class FileAttachmentsContainer
  {
    private readonly List<FileAttachment> _fileAttachments;

    public FileAttachmentsContainer()
    {
      _fileAttachments = new List<FileAttachment>();
    }

    public IEnumerable<FileAttachment> FileAttachments
    {
      get { return _fileAttachments; }
    }

    public void AddAttachment(FileAttachment fileAttachment)
    {
      _fileAttachments.Add(fileAttachment);
    }
  }

  public class FileAttachment
  {
    public string DownloadedPath { get; set; }
  }
}

根据您的错误消息，我想您的FileAttachment课程与您描述的不同。最终，您将列表传递给表达式，而不是保存列表的容器对象。