c# - 使用 except 方法比较两个列表

Question

我正在尝试将两个列表与 except 方法进行比较，但它不能正常工作：

List<Customer> PotentialSharedCustomer = new List<Customer>();
PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "01234", Name = "Hans Jürgen" });
PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "05465", Name = "Beate Müller" });
PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "15645", Name = "Sabine Meyer" });
PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "54654", Name = "Moritz Kummerfeld" });
PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "15647", Name = "Hanna Testname" });

List<Customer> ActualSharedCustomer = new List<Customer>();
ActualSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "01234", Name = "Hans Jürgen" });
ActualSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "05465", Name = "Beate Müller" });
ActualSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "15645", Name = "Sabine Meyer" });

PrepareCreateSharedCustomer(PotentialSharedCustomer, ActualSharedCustomer);

public void PrepareCreateSharedCustomer(List<Customer> potentialSharedCustomer, List<Customer> actualSharedCustomer)
{
    List<Customer> result = potentialSharedCustomer.Except(actualSharedCustomer).ToList<Customer>();
}

变量“result”的结果应该是“PotentialSharedCustomers”的所有记录，列表中没有“ActialSharedCustomer”：

PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "54654", Name = "Moritz Kummerfeld" });
PotentialSharedCustomer.Add(new Customer { AccountId = Guid.Empty, AccountNumber = "15647", Name = "Hanna Testname" });

我认为“除外”是解决此问题的正确方法，但我得到了“PotentialSharedCustomer”的所有项目的退货

谢谢帮助

Answer 1

一种不覆盖Equals或编写自定义IEqualityComparer的方法是获取标识符列表，然后过滤您的列表：

List<string> accountNumbers = 
    potentialSharedCustomer.Select(c => c.AccountNumber)
                           .Except(actualSharedCustomer.Select(c => c.AccountNumber));

List<Customer> result = potentialSharedCustomer.Where(c => accountNumbers.Contains(c.AccountNumber));

您可以查看其他数据结构，例如HashSet提高查找性能，但如果大小很小，这可能就足够了。

Answer 2

Customer应该实现IEquatable<Customer>，这意味着您必须实现public bool Equals(Customer other)（如果other等于，则返回 true this），并且public int GetHashCode().

查看文档以获取示例：http: //msdn.microsoft.com/en-us/library/bb300779.aspx

还有其他 StackOverflow 答案示例了如何GetHashCode()实现：https ://stackoverflow.com/a/263416/62802 。

Answer 3

var distinctCustomer = PotentialSharedCustomer
    .Select(p => p.AccountNumber)
    .Except(actualSharedCustomer.Select(q => q.AccountNumber))
    .ToList();