LINQ 加入使用日期不起作用

Question

我正在尝试基于两个单独的列表创建单个项目列表，但 ListA 中的日期属性与 ListB 中的不同日期属性具有相同的值。我从我的 FinalList 中的 ListB 中获得了正确的对象，但不是 ListA 中的对象。

考虑以下数据

Public Class Foo
    Public Property InstallDate  As Nullable(Of Date)
       'getters/ setters 
    End Property
    Public Property RemovalDate  As Nullable(Of Date)
       'getters/ setters 
    End Property
End Class

Dim Foo1 As New Foo()
Foo1.InstallDate = 01/12/2014
Foo1.RemovalDate = Nothing

Dim Foo2 As New Foo() 
Foo2.InstallDate = 02/12/2014
Foo2.RemovalDate = Nothing

Dim Foo3 As New Foo()
Foo3.InstallDate = 01/01/2001
Foo3.RemovalDate = 01/12/2014

Dim OriginalList As IList(Of Foo) = {
   Foo1,
   Foo2,
   Foo3
}

还有我的代码

    Dim ListA As IList(Of Foo) =
        (From X In OriginalList
        Where X.InstallDate IsNot Nothing And X.RemovalDate Is Nothing
        Select X).ToList()

    Dim ListB As IList(Of Foo) =
        (From X In OriginalList
        Where X.RemovalDate IsNot Nothing
        Select X).ToList()

    Dim FinalList As IList(Of Foo) =
        (From LA In ListA
        Group Join LB In ListB On ListA.InstallDate Equals ListB.RemovalDate Into Group _
        From grp In Group.DefaultIfEmpty()
        Select grp).ToList()

所以我期望 FinalList 包含对象 Foo1 和 Foo3 但我只得到 Foo3

知道我做错了什么吗？

Answer 1

我已更正您的代码：

Public Class Foo
    Public Property InstallDate  As Nullable(Of Date)
    Public Property RemovalDate  As Nullable(Of Date)
End Class

Dim Foo1 As New Foo()
Foo1.InstallDate = #01/12/2014#
Foo1.RemovalDate = Nothing

Dim Foo2 As New Foo() 
Foo2.InstallDate = #02/12/2014#
Foo2.RemovalDate = Nothing

Dim Foo3 As New Foo()
Foo3.InstallDate = #01/01/2001#
Foo3.RemovalDate = #1/12/2014#

Dim OriginalList As IList(Of Foo) = {
    Foo1,
    Foo2,
    Foo3
}

Dim ListA = (From X In OriginalList
             Where X.InstallDate IsNot Nothing AndAlso X.RemovalDate Is Nothing
             Select X).ToList()

Dim ListB = (From X In OriginalList
             Where X.RemovalDate IsNot Nothing
             Select X).ToList()

因此，要获得 Foo1 和 Foo3，请执行简单的 Join:

Dim FinalList = (From LA In ListA
                 Join LB In ListB On LA.InstallDate Equals LB.RemovalDate).ToList()

FinalList 现在包含具有两个属性的单个项目（因为只有一个匹配项）：

LA (Foo1) 和 LB (Foo2)

回复您的评论：

要展平列表，只需使用：

Dim FinalList = From LA In ListA
                Join LB In ListB On LA.InstallDate Equals LB.RemovalDate
                From item in {LA, LB}
                Select item

LINQ 加入使用日期不起作用

LINQ join using dates not working

linq

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