vb.net Linq实战

VB.net 提供了通过Linq对数据集进行合计非常方法，可以减少了与数据库的交互，提高系统性能，以下是sum示示例：

1、对字典对象的sum

dis.Sum(Function(a) a.Value) 'dis是Dictionary
当然也可以用 
Mytb.Compute("Sum(USM_TOTAL_CASH_MONEY)", "")2、对datatable的单字段sum
(From row In tmptable Select row.Field(Of Decimal)("customer_ds")).Sum() '
tmptable是DataTable对象,customer_ds是合计字段
3、对DataTable的多字段sum
 Dim sumtable2 = From r In MyTb               Group r By Key = New With {Key .Key = "合计"} Into g = Group              Select New With {.key = Key,                               .totalMoney = g.Sum(Function(x) IIf(IsDBNull(x("A1")), 0, x("A1"))),                               .saleMoney = g.Sum(Function(x) IIf(IsDBNull(x("A2")), 0, x("A2"))),                               .CaSh = g.Sum(Function(x) IIf(IsDBNull(x("A3")), 0, x("A3"))),                               .CardPay = g.Sum(Function(x) IIf(IsDBNull(x("A4")), 0, x("A4"))),                               .OtherPay = g.Sum(Function(x) IIf(IsDBNull(x("A5")), 0, x("A5"))),                               .CkPay = g.Sum(Function(x) IIf(IsDBNull(x("A6")), 0, x("A6"))),                               .DyqPay = g.Sum(Function(x) IIf(IsDBNull(x("A7")), 0, x("A7"))),                               .Minus = g.Sum(Function(x) IIf(IsDBNull(x("A8")), 0, x("A8"))),                               .orders = g.Sum(Function(x) IIf(IsDBNull(x("A9")), 0, x("A9"))),                               .newCards = g.Sum(Function(x) IIf(IsDBNull(x("A10").ToString().Split("/")(0)), 0, x("A11").ToString().Split("/")(0))) & "/" &                                           g.Sum(Function(x) IIf(IsDBNull(x("A11").ToString().Split("/")(1)), 0, x("A11).ToString().Split("/")(1))),        .cardInNums = g.Sum(Function(x) IIf(IsDBNull(x("充卡张数/金额").ToString().Split("/")(0)), 0, x("充卡张数/金额").ToString().Split("/")(0))) & "/" &                     g.Sum(Function(x) IIf(IsDBNull(x("充卡张数/金额").ToString().Split("/")(1)), 0, x("充卡张数/金额").ToString().Split("/")(1)))                              }