c# – 用于Annoymous类型的IEqualityComparer

首先我看到了 IEqualityComparer for anonymous type并且那里的答案没有回答我的问题,因为显而易见的原因是我需要IEqualityComparer而不是IComparer用于Linq的Distinct()方法.我也检查了其他答案,这些都没有解决方案……

问题

我有一些代码来操作和从DataTable中提取记录

var glext = m_dtGLExt.AsEnumerable();
var cflist =
    (from c in glext
     orderby c.Field<string>(m_strpcCCType),c.Field<string>(m_strpcCC),c.Field<string>(m_strpcCCDesc),c.Field<string>(m_strpcCostItem)
     select new
     {
        CCType = c.Field<string>(m_strpcCCType),CC = c.Field<string>(m_strpcCC),CCDesc = c.Field<string>(m_strpcCCDesc),CostItem = c.Field<string>(m_strpcCostItem)
     }).Distinct();

但是我需要使用不同的方法来区分大小写.这里扔我的是使用匿名类型.

尝试解决方案1

如果我有SomeClass有明显的具体对象我可以做

public class SumObject
{
    public string CCType { get; set; }
    public string CC { get; set; }
    public string CCDesc { get; set; }
    public string CostItem { get; set; }
}

我显然可以做到这一点

List<SumObject> lso = new List<SumObject>() 
{
    new SumObject() { CCType = "1-OCC",CC = "300401",CCDesc = "Rooney",CostItem = "I477" },new SumObject() { CCType = "1-OCC",CCDesc = "Zidane",CostItem = "I677" },CCDesc = "Falcao",CostItem = "I470" },};
var e = lso.Distinct(new SumObjectComparer()); // Great :]

哪里

class SumObjectComparer : IEqualityComparer<SumObject>
{
    public bool Equals(SumObject x,SumObject y)
    {
        if (Object.ReferenceEquals(x,y)) 
            return true;
        if (Object.ReferenceEquals(x,null) || Object.ReferenceEquals(y,null))
            return false;
        return x.CCType.CompareNoCase(y.CCType) == 0 && 
               x.CC.CompareNoCase(y.CC) == 0 && 
               x.CCDesc.CompareNoCase(y.CCDesc) == 0 && 
               x.CostItem.CompareNoCase(y.CostItem) == 0;
    }
 
    public int GetHashCode(SumObject o)
    {
        if (Object.ReferenceEquals(o,null)) 
            return 0;
        int hashCCType = String.IsNullOrEmpty(o.CCType) ? 
            0 : o.CCType.ToLower().GetHashCode();
        int hashCC = String.IsNullOrEmpty(o.CC) ? 
            0 : o.CC.ToLower().GetHashCode();
        int hashCCDesc = String.IsNullOrEmpty(o.CCDesc) ? 
            0 : o.CCDesc.ToLower().GetHashCode();
        int hashCostItem = String.IsNullOrEmpty(o.CostItem) ? 
            0 : o.CostItem.ToLower().GetHashCode();
        return hashCCType ^ hashCC ^ hashCCDesc ^ hashCostItem;
    }
}

但是,在上面的Linq查询中使用匿名类型会让我失望.

尝试解决方案2

为了尝试另一个解决方案(因为我在其他地方有相同的问题),我生成了以下通用比较器类

public class GenericEqualityComparer<T> : IEqualityComparer<T>
{
    Func<T,T,bool> compareFunction;
    Func<T,int> hashFunction;
 
    public GenericEqualityComparer(Func<T,bool> compareFunction,Func<T,int> hashFunction)
    {
        this.compareFunction = compareFunction;
        this.hashFunction = hashFunction;
    }
 
    public bool Equals(T x,T y) { return compareFunction(x,y); }
    public int GetHashCode(T obj) { return hashFunction(obj); }
}

所以我可以尝试做

var comparer = new GenericEqualityComparer<dynamic>(
    (x,y) => { /* My equality stuff */ },o => { /* My hash stuff */ });

但是这会将返回的值转换为IEnumerable< dynamic>这反过来影响我即将使用的cflist,因此在以下查询中,连接失败.

var cf = 
    (from o in cflist
     join od in glext
     on new { o.CCType,o.CC,o.CCDesc,o.CostItem } equals new
     {
        CCType = od.Field<string>(m_strpcCCType),CC = od.Field<string>(m_strpcCC),CCDesc = od.Field<string>(m_strpcCCDesc),CostItem = od.Field<string>(m_strpcCostItem)
     }
     into c
     select new { ... }

由于大量使用此代码,我不想进入IEnumerable< T> s进行丑陋的转换…

题

有没有办法可以为我的匿名类型创建IEquailityComparer？

谢谢你的时间.

解决方法

Is there a way I can create my an IEquailityComparer for my anonymous types?

当然.您只需要使用类型推断.例如,你可以有类似的东西：

public static class InferredEqualityComparer
{
    public static IEqualityComparer<T> Create<T>(
        IEnumerable<T> example,bool> equalityCheck,int> hashCodeProvider)
    {
        return new EqualityComparerImpl<T>(equalityCheck,hashCodeProvider);
    }
 
    private sealed class EqualityComparerImpl<T> : IEqualityComparer<T>
    {
        // Implement in the obvIoUs way,remembering the delegates and
        // calling them appropriately.
    }
}

然后：

var glext = m_dtGLExt.AsEnumerable();
var query = from c in glext
            orderby ...
            select new { ... };
var comparer = InferredEqualityComparer.Create(query,(x,y) => { ... },o => { ... }
);
var distinct = query.Distinct(comparer);

基本上,该方法的第一个参数仅用于类型推断,因此编译器可以计算出用于lambda表达式参数的类型.

您可以通过创建匿名类型的示例来提前创建比较器：

var sample = new[] { new { ... } };
var comparer = InferredExqualityComparer.Create(sample,...);
var distinct = (... query here ... ).Distinct(comparer);

但是每当你改变查询时,你也必须改变样本.

c# – 用于Annoymous类型的IEqualityComparer

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