根据特定属性比较两个列表 [英] Comparing two lists according to specific properties

问题描述

我该如何比较2个列表，并根据具体属性选择不匹配的项目

how can i compare 2 lists and have the not matching items but according to the specifics properties

public partial class Cable : StateObject
{            
    public int Id { get; set; }
    public int CablePropertyId { get; set; }
    public int Item { get; set; }
    public int TagNo { get; set; }
    public string GeneralFormat { get; set; }
    public string EndString { get; set; }
    public string CableRevision { get; set; }         
}

如果要使用，我想根据CablePropertyId，TagNo和CableRevision比较完成的结果

I want to comparision accomplished accoring to the CablePropertyId,TagNo and CableRevision, if i use

var diffCables = sourceCables.Except(destinationCables).ToList();

将整个属性相互比较.我该怎么办?

the whole properties are compared to each other . how can i do that?

推荐答案

使用带有自定义EqualityComparer的方法除外的Linq.

Use Linq except method with custom EqualityComparer.

http://msdn.microsoft. com/en-us/library/bb336390(v = vs.110).aspx

class CableComparer : IEqualityComparer<Cable>
{
    public bool Equals(Cable x, Cable y)
    {
        return (x.CablePropertyId == y.CablePropertyId && ...);
    }

    public int GetHashCode(Cable x) // If you won't create a valid GetHashCode based on values you compare on, Linq won't work properly
    {
        unchecked
        {
            int hash = 17;
            hash = hash * 23 + x.CablePropertyID;
            hash = hash * 23 + ...
        }
        return hash;
    }
}

var diffCables = sourceCables.Except(destinationCables, new CableComparer());

此外，对结果执行ToList()并不是真正必要的.在大多数情况下，您可以仅对Linq查询IEnumerable的结果进行操作，而无需指定确切的类型.这样，您就不会在不必要的ToList()操作上浪费性能.

Also, ToList() operation on the result isn't really necessary. Most of the time you can just operate on the result of Linq query IEnumerable without specifying the exact type; this way you won't waste performance on unneeded ToList() operation.

顺便说一句，其他一些人提出了带有简单lambda的基于Where的查询.这样的解决方案更容易阅读(我认为)，但优化程度也较低:它强制执行n ^ 2检查，而IEqualityComparer允许使用GetHashCode()方法使Linq达到最佳状态.这是关于GetHashCode重要性的绝佳答案，这是

By the way, a couple of others proposed Where-based queries with simple lambda. Such solution is easier to read (in my opinion), but it's also less optimized: it forces n^2 checks, while IEqualityComparer allows Linq to be more optimal because of GetHashCode() method. Here's a great answer on importance of GetHashCode, and here's a great guide on writing GetHashCode() override.

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