Question

操作系统：Windows Phone 7.5 语言：使用Visual Studio 2010的VB.NET

问题：我在教师和课程之间有一对多的关系。一位老师可以教一到多门课程。尝试更新或删除时，我会收到invalidoperationexception。

如何重现错误：

点击CreateButton。数据库已创建。
点击InsertButton。正确插入所有数据。
点击ViewButton。到目前为止，一切都很好。
点击Modify。我在这里得到了例外。不知道为什么？
点击DeleteButton。我在这里得到了同样的例外。不知道为什么？

以下是代码：

Partial Public Class MainPage
Inherits PhoneApplicationPage

' One Teacher can teach one or more Courses. One-To-Many relationship

Private db As AppContext

Public Sub New()
    InitializeComponent()
End Sub

Private Sub CreateButton_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles CreateButton.Click

    Try
        db = New AppContext("DataSource=isostore:/CCNB.sdf")

        If db.DatabaseExists Then
            db.DeleteDatabase()
        End If

        db.CreateDatabase()

    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try

End Sub

Private Sub InsertButton_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles InsertButton.Click

    Try
        Dim oTeacher1, oTeacher2 As New Teacher

        Dim oCourse1, oCourse2, oCourse3 As New Course

        ' Add courses

        oCourse1.CourseName = "VB.NET"
        oCourse2.CourseName = "Windows Phone"
        oCourse3.CourseName = "Analyse"

        db.Courses.InsertOnSubmit(oCourse1)
        db.Courses.InsertOnSubmit(oCourse2)
        db.Courses.InsertOnSubmit(oCourse3)

        ' Add teachers

        With oTeacher1
            .TeacherName = "Mike Jones"
            .Courses.Add(oCourse1)
            .Courses.Add(oCourse2)
        End With

        With oTeacher2
            .TeacherName = "Sam Roy"
            .Courses.Add(oCourse3)
        End With

        db.Teachers.InsertOnSubmit(oTeacher1)
        db.Teachers.InsertOnSubmit(oTeacher2)

        db.SubmitChanges()

    Catch dbException As Exception
        MessageBox.Show(dbException.Message)
    End Try

End Sub

Private Sub ViewButton_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles ViewButton.Click

    Dim Output As New StringBuilder
    Dim TeachersCourses = From oTeacher In db.Teachers

    For Each oTeacher In TeachersCourses.ToArray
        Output.Append("Teacher: " & oTeacher.TeacherID & " " & oTeacher.TeacherName & Environment.NewLine)

        Output.Append("Number of courses: " & oTeacher.Courses.Count & Environment.NewLine)
        For Each oCourse In oTeacher.Courses
            Output.AppendFormat(vbTab & oCourse.CourseName & Environment.NewLine)
        Next
    Next

    MessageBox.Show(Output.ToString)

End Sub

Private Sub DeleteButton_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles DeleteButton.Click

    Try

        Dim TeacherIDToDelete As Integer = 2    ' 2 = second teacher

        For Each oTeacher In db.Teachers

            If oTeacher.TeacherID = TeacherIDToDelete Then

                For Each oCourse In oTeacher.Courses
                    db.Courses.DeleteOnSubmit(oCourse)
                Next

                db.Teachers.DeleteOnSubmit(oTeacher)

            End If

        Next

        ' Keep getting invalidoperationexception. Reason why: ???
        db.SubmitChanges()

        MessageBox.Show(" Deleted")

    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try

End Sub

Private Sub UpdateButton_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles UpdateButton.Click

    Try

        Dim TeacherIDToModify As Integer = 2    ' 2 = Second teacher

        Dim oTeacherModify = (From oTeacher In db.Teachers
          Where oTeacher.TeacherID = TeacherIDToModify
          Select oTeacher).First

        oTeacherModify.TeacherName = "John Doe"

        ' Keep getting invalidoperationexception. Reason why: ???
        db.SubmitChanges()

        MessageBox.Show("Mise à jour effectuée")

    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try

End Sub


Private Sub CloseButton_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles CloseButton.Click

    db.Dispose()

End Sub

End Class

#Region "Database structure"

Public Class AppContext
Inherits DataContext

Public Teachers As Table(Of Teacher)
Public Courses As Table(Of Course)

Public Sub New(ByVal connectionString As String)
    MyBase.New(connectionString)
End Sub

End Class

<Table(Name:="Teacher")>
Public Class Teacher

' Primary Key
Private TeacherIDInteger As Integer

<Column(DbType:="INT NOT NULL IDENTITY", IsPrimaryKey:=True, IsDBGenerated:=True, CanBeNull:=False, AutoSync:=AutoSync.OnInsert)>
Public Property TeacherID() As Integer
    Get
        Return TeacherIDInteger
    End Get
    Set(ByVal value As Integer)
        TeacherIDInteger = value
    End Set
End Property

Private TeacherNameString As String

<Column()>
Public Property TeacherName() As String
    Get
        Return TeacherNameString
    End Get
    Set(ByVal value As String)
        TeacherNameString = value
    End Set
End Property

' One-to-many relationship with Courses
Private CourseEntitySet As New EntitySet(Of Course)

<Column()>
<Association(Storage:="CourseEntitySet", ThisKey:="TeacherID", OtherKey:="TeacherID")>
Public Property Courses() As EntitySet(Of Course)
    Get
        Return Me.CourseEntitySet
    End Get
    Set(value As EntitySet(Of Course))
        Me.CourseEntitySet.Assign(value)
    End Set
End Property

End Class

<Table(Name:="Course")>
Public Class Course

' Primary Key
Private CourseIDInteger As Integer

<Column(DbType:="INT NOT NULL IDENTITY", IsPrimaryKey:=True, IsDBGenerated:=True, _
 CanBeNull:=False, AutoSync:=AutoSync.OnInsert)>
Public Property CourseID() As Integer
    Get
        Return CourseIDInteger
    End Get
    Set(ByVal value As Integer)
        CourseIDInteger = value
    End Set
End Property

Private CourseNametring As String

<Column()>
Public Property CourseName() As String
    Get
        Return CourseNametring
    End Get
    Set(ByVal value As String)
        CourseNametring = value
    End Set
End Property

' Foreign key
Private TeacherIDInteger As Integer

<Column()>
Public Property TeacherID() As Integer
    Get
        Return TeacherIDInteger
    End Get
    Set(ByVal value As Integer)
        TeacherIDInteger = value
    End Set
End Property

End Class

#End Region

更新或删除时，DataContext.SubmitChanges会导致invalidoperationexception

0 个答案: