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，但其中ListA的日期属性与ListB中的不同日期属性的值相同。我在FinalList中从ListB获取了正确的对象，但没有在ListA中获取对象。

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
}

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()

所以我希望FinalList包含对象Foo1和Foo3，但我只得到Foo3

任何想法我做错了什么？

Answer 1

我已经更正了您的代码：

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()

所以，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现在包含一个项目（因为只有一个匹配），有两个属性：

LA（Foo1）和LB（Foo2）

---

回应你的评论：

要展开列表，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