c# - 如果我的条件匹配，如何从另一个列表中选择项目？

Question

我对 C# 列表有疑问。

我有两种不同类型的列表(account 和 accountDescriptionHistory)。 accountID 和 accountdescription 两列均出现在列表中。

var account = new List<Account>();
var accountDescriptionHistory = new List<AccountDescriptionHistory>();

现在，我想根据以下条件准备一个结果列表。

1. 如果 accountID 匹配，请从 accountDescriptionHistory 列表中选择一个帐户描述。
2. 结果列表应为List()类型；

类定义

public class Account
{

    /// <summary>
    /// The account number
    /// </summary>
    public virtual string AccountNumber { get; set; }

    /// <summary>
    /// The account's description
    /// </summary>
    public virtual string Description { get; set; }
}

帐户描述类:

    public class AccountDescriptionHistory : EntityModel<AccountDescriptionHistory>
    {
        #region Public Properties

        /// <summary>
        /// The account description of an account that is valid for a specific date range
        /// </summary>
        public virtual string AccountDescription { get; set; }

        /// <summary>
        /// The account this AccountDescriptionHistory is associated with.
        /// </summary>
        public virtual Account Account { get; set; }
}

Answer 1

您的问题不清楚确切的输出。话虽如此。

给定

List<Account> accounts = new List<Account>
{ 
    new Account {AccountNumber = "1", Description = "Account 1"}, 
    new Account {AccountNumber = "2", Description = "Account 2"},
    new Account {AccountNumber = "4", Description = "Account 4"}, 
};

List<AccountDescriptionHistory> accountHistories = new List<AccountDescriptionHistory>
{ 
    new AccountDescriptionHistory {AccountDescription = "History Account 1", Account = accounts[0] }, 
    new AccountDescriptionHistory {AccountDescription = "History Account 2", Account = accounts[1] }, 
    new AccountDescriptionHistory {AccountDescription = "History Account 3", Account = new Account {AccountNumber = "3", Description = "Account 3"} }, 
};

我们想要使用 AccountNumber 查找 accounts 中存在的所有 accountHistories，我们可以编写一个 Where 子句来查找所有这些:

List<AccountDescriptionHistory> result = accountHistories
    .Where(x => accounts.Any(y => y.AccountNumber == x.Account.AccountNumber))
    .ToList();

如果您只想从结果中检索 AccountDescription，您可以编写:

List<string> result = accountHistories
    .Where(x => accounts.Any(y => y.AccountNumber == x.Account.AccountNumber))
    .Select(x => x.AccountDescription)
    .ToList();

如果您希望将结果转换为具有 AccountDescriptionHistory 描述的 Account，您可以执行以下操作:

List<Account> result = accountHistories
    .Where(x => accounts.Any(y => y.AccountNumber == x.Account.AccountNumber))
    .Select(x => new Account {AccountNumber = x.Account.AccountNumber, Description = x.AccountDescription})
    .ToList();

编辑

您可以创建这样的函数:

static Account WithDescriptionHistory(Account account, IEnumerable<AccountDescriptionHistory> accountHistories)
{
    AccountDescriptionHistory accountHistory = accountHistories.FirstOrDefault(x => x.Account.AccountNumber == account.AccountNumber);
    account.Description = accountHistory?.AccountDescription ?? account.Description;
    return account;
}

然后将原始的 account 变量转换为:

accounts = accounts
    .Select(x => WithDescriptionHistory(x, accountHistories))
    .ToList();

输出

History Account 1
History Account 2
Account 4