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
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.
