從LINQ添加附加值

Question

我有以下代碼：

var checkRegisters = await Database.Client.Context.CheckRegister
            .Where(cr => cr.CheckingAccount == account 
                   && cr.CheckDate >= fromDate 
                   && cr.CheckDate <= toDate 
                   && cr.Void == "N" )
            .GroupBy(cr => cr.CheckNumber, 
                     cr => cr.Amount, (key, g) => 
                                          new { 
                                                CheckNumber = key, 
                                                Amount = g.Sum()
                                              })
            .OrderBy(c => c.CheckNumber)
            .ToListAsync();

除了向我返回CheckNumber和Amount的列表之外，我還不太了解它在做什么。 CheckRegister表包含“收款人”列，EF中的相應modelBuilder也是如此：

entity.Property(e => e.Payee).HasColumnType("varchar(255)");

如何將“收款人”添加到返回的列表中？

Answer 1

代碼的作用是：

您的數據庫有一個包含CheckRegisters的表。 每個CheckRegister至少具有屬性CheckingAccount ， CheckDate ， Void ， CheckNumber和Amount ，並且根據您的情況，還具有一個Payee屬性：

因此，您的代碼將逐步描述。

// Take the complete table of CheckRegisters:
Database.Client.Context.CheckRegister

// from every checkRegister in this table (every row),
// keep only those checkRegisters that have a CheckingAccount value equal to account
// and a CheckDate value betwen fromData and toDate
// and a value for property Void equalt to "N"

.Where(checkRegister => checkRegister.CheckingAccount == account 
                     && checkRegister.CheckDate >= fromDate 
                     && checkRegister.CheckDate <= toDate 
                     && checkRegister.Void == "N" )

// Group all remaining CheckRegisters into groups with same checkNumber
// Each group will have a property Key which has the value of the common CheckNumber
        .GroupBy(cr => cr.CheckNumber,

           // ElementSelector: from every CheckRegister put only the amount in each grouop 
           checkRegister => checkRegister.Amount,

           // ResultSelector: take every key (which we call checkNumber)
           // and all Amounts of all CheckRegisters with this CheckNumber
           // to make one new object:
           (checkNumber, amountsFromCheckRegistersWithThisCheckNumber) => new
           { 
                CheckNumber = key, 

                // To calculate property Amount: sum all amountsFromCheckRegistersWithThisCheckNumber
                Amount = amountsFromCheckRegistersWithThisCheckNumber.Sum(),
           })

// By now you have a sequence of objects, each with two properties:
// CheckNumber: a checkNumber used in the CheckRegisters that were left after the Where
// Amount: the sum of all Amounts of all CheckRegisters that have this CheckNumber

// Finally you do some Ordering, and convert the resulting elements into a list
.OrderBy(groupedItem => groupedItem.CheckNumber)
.ToListAsync();

現在，您需要進行更改：添加Payees 。

問題是，返回的數據是按CheckNumber分組的CheckRegisters。 每個收款人都是每個CheckRegister。 如果將具有相同CheckNumber的CheckRegisters組組成，則具有此CheckNumber的幾位收款人：

CheckNumber | Payee | ...
    1       |   A
    2       |   B
    1       |   C
    2       |   C    // note: C  is used again
    1       |   D

如果我使用相同的CheckNumber進行分組，您將獲得：

group CheckNumber 1 [1, A], [1,C], [1,D]
group CheckNumber 2 [2, B], [2,C]

因此，每個組可能有不止一個員工。 如果可以的話，只需省略ElementSelector並在ResultSelector中選擇雇員

var result = Database.Client.Context.CheckRegister
.Where(...)
.GroupBy(cr => cr.CheckNumber,

// ResultSelector: take every key (which we call checkNumber)
// and all CheckRegisters with this CheckNumber
// to make one new object:
(checkNumber, checkRegistersWithThisCheckNumber) => new
{ 
    CheckNumber = checkNumber, 

    // for Employees: Select property Employee, and convert them to a List
    Employees = checkRegistersWithThisCheckNumber
                .Select(checkRegister => checkRegister.Employee)
                .ToList(),

    // Amounts: select the Amounts and Sum
    Amount = checkRegistersWithThisCheckNumber
                 .Select(checkRegister => checkRegister.Amount)
                 .Sum(),
    });

Answer 2

我會將其添加到您在GroupBy中創建的對象中。 所以像下面這樣改變第3行

.GroupBy(cr => cr.CheckNumber, cr => cr.Amount, cr => cr.Payee, (key, g) => 
                              new { CheckNumber = key, Amount = g.Sum(), Payee = g.Payee})

請注意，分組依據只是按數字和金額分隔，因此，如果您也按收款人分組，則應該預期結果列表會更長。 這也假設收款人是表中列的名稱。

Answer 3

通過以下方式將新列添加到組中：

var checkRegisters = await Database.Client.Context.CheckRegister
            .Where(cr => cr.CheckingAccount == account && cr.CheckDate >= fromDate && cr.CheckDate <= toDate && cr.Void == "N" )
            .GroupBy(cr => cr.CheckNumber, cr => cr.Amount, e => e.Payee , (key, g, p) => new { CheckNumber = key, Amount = g.Sum(), Payee = p})
            .OrderBy(c => c.CheckNumber).ToListAsync();