当一个还没有 Id 时，C# 中是否有一种方法可以使用 EXCEPT 来比较 2 个列表？

如何解决当一个还没有 Id 时，C# 中是否有一种方法可以使用 EXCEPT 来比较 2 个列表？

我从数据库中得到 listA。我从最终用户上传的文件中获取 listB，我将其转换为列表中的正确类。例如，我给你一个来自数据库和用户上传的列表。您可以在下面找到这些示例。

我需要检查 listB 是否在 listA 中，但是当我使用 Except 时，我得到了整个列表，因为 Id 不在 listB 中（数据库中的自动编号）。我现在有一个解决方案，但有没有更好的方法来做到这一点？

到目前为止我尝试过的：

List<CustomerGroup> listC = listA.Except(listB).ToList(); 
    //Returns listA in listC because Id isn't the same

这就是我现在用的，但看起来很多余。

foreach (CustomerGroup itemtocheck in listB)
{
    var foundItem = listA.Find(dbItem => dbItem.FirstName== itemtocheck.FirstName &&
                                            dbItem.FamilyName== itemtocheck.FamilyName &&
                                            dbItem.Quantity == itemtocheck.Quantity &&
                                            dbItem.discount == itemtocheck.discount);
    if(foundItem != null)
    {
        listA.Remove(foundItem);
        listB.Remove(itemtocheck);
    }
}

foreach (CustomerGroup itemtocheck in listB)
{
    // other code to check here
}

List<CustomerGroup> listA = new List<CustomerGroup>(){
   new CustomerGroup {Id = 1,FirstName = "Anna",FamilyName = "Shrek",Quantity = 5,discount = 10},new CustomerGroup {Id = 2,FirstName = "Elsa",FamilyName = "Fiona",new CustomerGroup {Id = 3,FirstName = "Olaf",FamilyName = "Donkey",new CustomerGroup {Id = 4,FirstName = "sven",FamilyName = "Dragon",discount = 5},new CustomerGroup {Id = 5,FirstName = "Kristoff",FamilyName = "Puss",new CustomerGroup {Id = 6,Quantity = 10,discount = 15},new CustomerGroup {Id = 7,discount = 30}
};

List<CustomerGroup> listB = new List<CustomerGroup>(){
   new CustomerGroup { FirstName = "Anna",new CustomerGroup { FirstName = "Elsa",discount = 8},new CustomerGroup { FirstName = "sven",new CustomerGroup { FirstName = "Kristoff",discount = 30},new CustomerGroup { FirstName = "Hans",FamilyName = "Farquaad",Quantity = 20,discount = 40}
};

public class CustomerGroup{
    public int Id {get; set;}
    public string FirstName {get; set;}
    public string FamilyName {get; set;}
    public int Quantity{get; set;}
    public int discount {get; set;}
}

解决方法

您可以使用自己的 IEqualityComparer，忽略 ID 属性：

class MyEqualityComparer : IEqualityComparer<CustomerGroup>
{
    public bool Equals(CustomerGroup x,CustomerGroup y)
    {
        if(x is null) return y is null;
        if(y is null) return false;
        return x.FirstName == y.FirstName && x.FamilyName == y.FamilyName && x.Quantity == y.Quantity && x.Discount == y.Discount;
    }
    
    public int GetHashCode(CustomerGroup codeh)
    {
        return 0;
    }
}

将此传递给Except：

List<CustomerGroup> listC = listA.Except(listB,new MyEqualityComparer()).ToList();

在线演示：https://dotnetfiddle.net/gogy9g

,

为类 false 实现 IEqualityComparer<>，然后使用 CustomerGroup，

喜欢

Except()

现在试试public class CompareCustomerGroup : IEqualityComparer<CustomerGroup> { public bool Equals(CustomerGroup dbCustomer,CustomerGroup uploadedCustomer) { if(dbCustomer == null || uploadedCustomer == null) return false; else return dbCustomer.FirstName == uploadCustomer.FirstName && dbCustomer.FamilyName == uploadCustomer.FamilyName && dbCustomer.Quantity == uploadCustomer.Quantity && dbCustomer.Discount == uploadCustomer.Discount; } public int GetHashCode(CustomerGroup customGroup) { return HashCode.Combine(customGroup.FirstName,customGroup.FamilyName,customGroup.Quantity,customGroup.Discount); } } ，

Except()