database VB.NET 中的“ConnectionString 属性尚未初始化”错误

"The ConnectionString property has not been initialized" error in VB.NET

提问by CompleteNewb

Every time I tried to connect to the database it give me this error "The ConnectionString property has not been initialized"

每次我尝试连接到数据库时，它都会给我这个错误“ConnectionString 属性尚未初始化”

what can I do to solve this?

我能做些什么来解决这个问题？

here are my codes

这是我的代码

Module Module1
    Function GetInfoForStudent(ByRef QueryName As String, ByVal UserName As String, ByVal Password As String) As DataTable
        Using Con As New SqlConnection
            Try
                Using OleCon As New SqlConnection
                    Dim Connection As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=G:\VB Project\Library
Catalog System\Library Catalog System\library.mdf;Integrated
Security=True;Connect Timeout=30;User Instance=True"
                    Con.Open()
                    Dim Cmd As SqlCommand = Con.CreateCommand()
                    Cmd.CommandType = CommandType.StoredProcedure
                    Cmd.CommandText = QueryName
                    Cmd.Parameters.AddWithValue("@user", UserName)
                    Cmd.Parameters.AddWithValue("@pass", Password)
                    Dim da As New SqlDataAdapter(Cmd)
                    Dim ds As New DataTable()
                    da.Fill(ds)
                    Return ds
                End Using
            Catch ex As Exception

                Throw New Exception(ex.Message)
            End Try
        End Using

    End Function

End Module

Sub ShowStudentInfo()
    Dim dt As DataTable = GetInfoForStudent("MyStoredProcName", "@user", "@pass")
    ' Since (presumably) only one is returned
    With dt.Rows(0)
        ' Assign your text boxes 
        StudentIDTextBox.Text = .Item("StudentID")
        LoginIDTextBox.Text = .Item("LoginID")
        Student_NameTextBox.Text = .Item("Student Name")
        Student_addressTextBox.Text = .Item("Student address")

    End With
End Sub

回答by JohnFx

You never assigned your connection string to the connection object, just like the error is saying.

您从未将连接字符串分配给连接对象，就像错误所说的那样。

Insert a line setting the connection string before con.open.

在 con.open 之前插入一行设置连接字符串。

Con.connectionstring = connection
Con.Open()

Or better yet, change your using statement as follows

或者更好的是，更改您的 using 语句如下

Dim Connection As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=G:\VB Project\Library Catalog System\Library Catalog System\library.mdf;Integrated
Security=True;Connect Timeout=30;User Instance=True"

Using Con As New SqlConnection(connection)

回答by bschultz

You are creating the connection string object but never assigning it to your SqlCommandobject.

您正在创建连接字符串对象，但从未将其分配给您的SqlCommand对象。