如何編寫LINQ查詢以使用C＃從另一個對象獲取對象？

Question

我將以下foreach循環轉換為LINQ語句。

foreach (Plant plant in Plant.ListPlants)
{
    foreach (Program program in plant.GetAllPrograms())
    {
        if (program.GetProfitCenter() != null)
        {
            foreach (CostCenter costCenter in program.GetProfitCenter().GetAllCostCenters())
            {
                foreach (Account account in costCenter.GetAccounts())
                {
                    if (account.Code == Code)//Code is a parameter
                    {
                        return account;
                    }
                }
            }
        }
    }
}

只要不存在此類帳戶代碼，結果應返回null。 請幫我構建上述循環的LINQ。

Answer 1

使用SelectMany

var accounts = Plant.ListPlants
    .SelectMany(lp => lp.GetAllPrograms())
    .Where(p => p.GetProfitCenter() != null)
    .SelectMany(p => p.GetProfitCenter().GetAllCostCenters())
    .SelectMany(cc => cc.GetAccounts())
    .Where(acc => acc.Code == Code);
return accounts.FirstOrDefault();

Answer 2

return (from plant in Plant.ListPlants
from program in plant.GetAllPrograms()
where program.GetProfitCenter() != null
from costCenter in program.GetProfitCenter().GetAllCostCenters()
from account in costCenter.GetAccounts()
where account.Code == Code
select account).FirstOrDefault();

這應該工作，我使用ReSharper功能將foreach轉換為LINQ，與toadflakz解決方案不同，它不應該在program.GetProfitCenter() == null時拋出異常。

Answer 3

它與您已編寫的代碼沒有什么不同，除非您最后進行了所有過濾。

var accounts = 
    from plant in Plant.ListPlants
    from program in plant.GetAllPrograms()
    from costCenter in program.GetProfitCenter().GetAllCostCenters()
    from account in costcenter.GetAccounts()
    where program.GetProfitCenter() != null && 
          account.Code == Code
    select account;
return accounts.FirstOrDefault();

我不能保證這會起作用，但它應該讓你知道從哪里開始。