Question

我想将两个列表与两个不同类的对象进行比较。这些是类：

namespace AngularWebApplication.Models
{
    public class AggregationLevelConfigurationPresentation
    {
        public byte AggregationLevelConfigurationId { get; set; }
        public int ProductionOrderId { get; set; }
        public string Name { get; set; }
        [ ... ]
    }
}

public class AggregationLevelConfiguration : IEquatable<AggregationLevelConfiguration>
{
    public byte AggregationLevelConfigurationId { get; set; }
    public int ProductionOrderId { get; set; }
    public string Name { get; set; }
    [ ... ]
}

我想让presentations列表中的元素不在currentLevels中：

列出演示文稿; 列出currentLevels;

List<Models.AggregationLevelConfigurationPresentation> newLevels =
    presentations
        .Select(l => new { l.AggregationLevelConfigurationId, l.ProductionOrderId })
        .Except(currentLevels.Select(l => new { l.AggregationLevelConfigurationId, l.ProductionOrderId }))
        .ToList();

但是当我执行Except时，我收到以下错误：

Error   CS0029  Cannot implicitly convert type 
'System.Collections.Generic.List<<anonymous type: byte AggregationLevelConfigurationId, int ProductionOrderId>>' to 
'System.Collections.Generic.List<AngularWebApplication.Models.AggregationLevelConfigurationPresentation>'

我认为问题出在new { l.AggregationLevelConfigurationId, l.ProductionOrderId }，但我不知道如何使用不同类别的对象列表来执行Except。

我需要presentations列表中的对象，currentLevels使用AggregationLevelConfigurationId和ProductionOrderId作为主键。

Answer 1

您的Execept - 查询会选择匿名类型，因此ToList不会创建List<AggregationLevelConfigurationPresentation>。您必须创建此类的实例：

List<AggregationLevelConfigurationPresentation> newLevels = presentations
        .Select(l => new { l.AggregationLevelConfigurationId, l.ProductionOrderId })
        .Except(currentLevels.Select(l => new { l.AggregationLevelConfigurationId, l.ProductionOrderId }))
        .Select(x => new AggregationLevelConfigurationPresentation 
        { 
            AggregationLevelConfigurationId = x.AggregationLevelConfigurationId,  
            ProductionOrderId = x.ProductionOrderId
         })
        .ToList();

我需要他们不在的演示文稿列表中的对象 currentLevels使用AggregationLevelConfigurationId和 ProductionOrderId作为主键。

然后你可以使用Join：

var except = presentations
        .Select(l => new { l.AggregationLevelConfigurationId, l.ProductionOrderId })
        .Except(currentLevels.Select(l => new { l.AggregationLevelConfigurationId, l.ProductionOrderId }));

var newLevels = from x in except
                join p in presentations 
                on x equals new { p.AggregationLevelConfigurationId, p.ProductionOrderId }
                select p;
List<AggregationLevelConfigurationPresentation> newLevelList = newLevels.ToList();

Answer 2

根据Evk评论，这就是我解决这个问题的方法：

List<Models.AggregationLevelConfigurationPresentation> newLevels =
     presentations.Where(p => !currentLevels.Any(l => p.AggregationLevelConfigurationId == l.AggregationLevelConfigurationId && p.ProductionOrderId == l.ProductionOrderId));

列表除了两个不同的类实例列表

2 个答案: