如何从 Dictionary<int, IEnumerable<Struct>> 中查找值答案

【问题标题】：How to find value from a Dictionary<int, IEnumerable<Struct>>如何从 Dictionary<int, IEnumerable<Struct>> 中查找值
【发布时间】：2014-08-22 11:00:43
【问题描述】：

我有一本字典 salaryFitmentDictionary，我想根据以下示例查询（linq 或 lambda）：其中 employeedId = 1 和 EarningDeductionId = 145 并获取余额的值 EDBalance。

我将如何实现这一目标？

var balance = salaryFitmentDictionary.Where...

Dictionary<int, IEnumerable<SalaryFitmentInfoMonth>> salaryFitmentDictionary = new Dictionary<int, IEnumerable<SalaryFitmentInfoMonth>>();

employeeIdList.ToList().ForEach(employeedId =>
{
    var perEmployeeFitments = from pf in _db.PayFitments.AsEnumerable()
                              join ed in _db.EarningDeductions.AsEnumerable()
                              on pf.EarningDeductionId equals ed.EarningDeductionId
                              where pf.EmployeeId == employeedId
                              select new SalaryFitmentInfoMonth
                              {
                                   EDId = pf.EarningDeductionId,
                                   EDAmount = pf.Amount,
                                   EDBalance = pf.Balance.GetValueOrDefault(),
                                   EDType = ed.EDType,
                                   IsTaxable = ed.IsTaxable,
                                   IsBenefit = ed.IsBenefit,
                                   IsLoan = ed.IsLoan,
                                   IsAdvance = ed.IsAdvance,
                                   Limit = ed.TaxIfMoreThan.GetValueOrDefault()
                              };

    salaryFitmentDictionary.Add(employeedId, perEmployeeFitments);
});

public struct SalaryFitmentInfoMonth
{
    public int EDId { get; set; }
    public decimal EDAmount { get; set; }
    public decimal? EDBalance { get; set; }
    public EarnDeduct EDType { get; set; }
    public bool IsTaxable { get; set; }
    public bool IsBenefit { get; set; }
    public bool IsLoan { get; set; }
    public bool IsAdvance { get; set; }
    public decimal? Limit { get; set; }
 }

【问题讨论】：

ToList().ForEachಠ_ಠ

标签： c# linq dictionary lambda

【解决方案1】：

IEnumerable<SalaryFitmentInfoMonth> salaries = salaryFitmentDictionary[1];
SalaryFitmentInfoMonth salary = salaries.FirstOrDefault(s => s.EDId == 45);

您应该处理salaryFitmentDictionary 不包含具有此ID 的情况。所以你可以改用TryGetValue。如果没有工资有这个EDIdFirstOrDefault返回null。

所以这里是更安全的版本：

IEnumerable<SalaryFitmentInfoMonth> salaries;
if(salaryFitmentDictionary.TryGetValue(1, out salaries))
{
    SalaryFitmentInfoMonth salary = salaries.FirstOrDefault(s => s.EDId == 45);
    if(salary != null) 
    {
        // do something ...
    }
}

如果您预计会有多个匹配项，您可以使用 Enumerable.Where 而不是 FirstOrDefault。

【讨论】：

【解决方案2】：

您可以在 LINQ 方法语法中使用 SelectMany 方法：

Int32 id = 1;
Int32 edId = 147;

var result = salaryFitmentDictionary.
    Where((pair) => pair.Key == id ).
    SelectMany((pair) =>
        pair.Value.Where((perEmployeeFitment) => perEmployeeFitment.EDId == edId)).
    Select(perEmployeeFitment => perEmployeeFitment.EDBalance).
    Single();

或者在查询语法中：

Int32 id = 1;
Int32 edId = 147;

var result = (from pair in salaryFitmentDictionary
    from perEmployeeFitment in pair.Value
    where pair.Key == id
    where perEmployeeFitment.EDId == edId
    select perEmployeeFitment.EDBalance).Single();

【讨论】：