从 LINQ 添加附加值

Question

我有以下代码：

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();

除了返回 CheckNumber 和 Amount 列表之外，我不完全理解它在做什么。 CheckRegister 表包含 Payee 列，EF 中相应的 modelBuilder 也是如此：

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

如何将收款人添加到我返回的列表中？

Answer 1

代码的作用：

您的数据库有一个包含CheckRegisters 的表。每个CheckRegister 至少有属性CheckingAccount、CheckDate、Void、CheckNumber 和Amount，据你说它还有一个属性Payee：

所以你的代码是一步一步描述的。

// 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();

现在您想要的更改：添加Payees。

问题是，返回的数据是按 CheckNumber 分组的 CheckRegisters。每个收款人都是每个 CheckRegister。如果您使用相同的 CheckNumber 将 CheckRegisters 分组，您将获得多个具有此 CheckNumber 的收款人：

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

如果我用相同的 CheckNumber 分组，你会得到：

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

所以每个组可能有多个员工。如果你没问题，只需省略 ElementSelector 并在 ResultSelector 中选择员工

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

我会将它添加到您在 GroupBy 中创建的对象中。所以像下面这样更改第 3 行

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

请注意，group by 仅按 Number 和 Amount 分隔，因此如果您还按 Payee 分组，您应该期望结果列表更长。这也假设 Payee 是表中列的名称。

Answer 3

将新列添加到组中：

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();