C# 中有没有办法在一个还没有 Id 的情况下使用 EXCEPT 来比较 2 个列表？

Question

我从数据库中得到 listA。我从最终用户上传的文件中获取 listB，然后将其转换为列表中的正确类。对于这个例子，我给你一个来自数据库的列表和一个用户上传的列表。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，我会得到整个列表，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，但有更好的方法吗？

到目前为止我所做的尝试：

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

这是我现在正在使用的，但它似乎很多余。

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", Quantity = 5, Discount = 10},
   new CustomerGroup {Id = 3, FirstName = "Olaf", FamilyName = "Donkey", Quantity = 5, Discount = 10},
   new CustomerGroup {Id = 4, FirstName = "Sven", FamilyName = "Dragon", Quantity = 5, Discount = 5},
   new CustomerGroup {Id = 5, FirstName = "Kristoff", FamilyName = "Puss", Quantity = 5, Discount = 10},
   new CustomerGroup {Id = 6, FirstName = "Sven", FamilyName = "Dragon", Quantity = 10, Discount = 15},
   new CustomerGroup {Id = 7, FirstName = "Kristoff", FamilyName = "Puss", Quantity = 10, Discount = 30}
};

List<CustomerGroup> listB = new List<CustomerGroup>(){
   new CustomerGroup { FirstName = "Anna", FamilyName = "Shrek", Quantity = 5, Discount = 10},
   new CustomerGroup { FirstName = "Elsa", FamilyName = "Fiona", Quantity = 5, Discount = 8},
   new CustomerGroup { FirstName = "Sven", FamilyName = "Dragon", Quantity = 5, Discount = 5},
   new CustomerGroup { FirstName = "Kristoff", FamilyName = "Puss", Quantity = 5, Discount = 10},
   new CustomerGroup { FirstName = "Sven", FamilyName = "Dragon", Quantity = 10, Discount = 15},
   new CustomerGroup { FirstName = "Kristoff", FamilyName = "Puss", Quantity = 10, 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;}
}

Answer 1

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

Answer 2

为类CustomerGroup实现IEqualityComparer<>，然后使用Except()，

喜欢，

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);
    }
} 

现在试试Except()，

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