MultipleActiveResultSets for SQL Server and VB.NET application - sql-server

Question

I am trying to get multiple data sets from SQL Server using a VB.NET application. The problem that every time I try to execute the query,
I get this message:
Cannot change property 'ConnectionString'. The current state of the connection is open
Then I tried to fix it by enabling MARS
<connectionStrings>
<add name="ConString"
providerName="System.Data.SqlClient"
connectionString="Data Source=my-PC;Initial Catalog=Project;Persist Security Info=True; MultipleActiveResultSets=true;User ID=user;Password=*****" />
</connectionStrings>
This is my code
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim obj, body
obj = TextBox1.Text
body = TextBox2.Text
For Each mail In getemail()
Send_mail(mail, obj, body, getattachment(mail))
Next
MsgBox("Traitement effectué")
End Sub
Function getemail() As List(Of String)
Dim strMailTo As New List(Of String)
Dim SQL As String = "Select EMail FROM [USER] WHERE EMail Is Not NULL And MatriculeSalarie Is Not NULL And [EMail] <> '' and EtatPaie = 3 and BulletinDematerialise = 1 "
Dim cmd As New SqlCommand
Dim sqLdr As SqlDataReader
Dim dr As DataRow
Try
ConnServer()
cmd.Connection = con
cmd.CommandText = SQL
Using sda As New SqlDataAdapter(cmd)
Using ds As New DataTable()
sda.Fill(ds)
sqLdr = cmd.ExecuteReader()
For i = 0 To ds.Rows.Count - 1
dr = ds.Rows(i)
strMailTo.Add(dr("EMail"))
Next
End Using
End Using
Return strMailTo
sqLdr.Close()
Catch ex As Exception
MsgBox(ex.Message.ToString)
End Try
closeCon()
Return strMailTo
End Function
Function getattachment(email) As String()
Dim SQL As String = "Select MatriculeSalarie FROM [USER] WHERE [EMail]='" & email & "'"
Dim cmd As New SqlCommand
Dim sqLdr As SqlDataReader
ConnServer()
cmd.Connection = con
cmd.CommandText = SQL
Dim mat As String
mat = ""
Dim Dir As String = ConfigurationManager.AppSettings("path1").ToString
Dim file()
sqLdr = cmd.ExecuteReader()
While sqLdr.Read
mat = sqLdr.GetValue(sqLdr.GetOrdinal("MatriculeSalarie"))
End While
file = IO.Directory.GetFiles(Dir, mat.Substring(1) & "*.pdf")
sqLdr.Close()
Return file
End Function

Answer 1

If all you are going to do is show a message box in a Catch, don't do it in the database code. Let the error bubble up to the user interface code and put the Try around where the method is called.
Do not declare variables without a DataType. The button code with Option Infer on sets the type of obj and body.
Private ConStr As String = "Your connection string"
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim obj = TextBox1.Text
Dim body = TextBox2.Text
Dim emails As New List(Of String)
Try
emails = getemail()
Catch ex As Exception
MessageBox.Show(ex.Message.ToString, "Error retrieving email list")
Exit Sub
End Try
For Each email In emails
Try
Send_mail(email, obj, body, getattachment(email))
Catch ex As Exception
MessageBox.Show(ex.Message, "Error getting attachments")
End Try
Next
MessageBox.Show("Traitement effectué")
End Sub
Parameters used by Sub and Function must have a DataType.
I don't know what you are doing here.
While sqLdr.Read
mat = sqLdr.GetValue(sqLdr.GetOrdinal("MatriculeSalarie"))
End While
Each iteration will overwrite the previous value of mat. I can only assume that you expect only a single value, in which case you can use ExecuteScalar to get the first column of the first row of the result set. Don't do anything with the data until after the connection is closed. Just get the raw data and close (End Using) the connection. Manipulate the data later.
Always use Parameters. Parameters are not treated as executable code by the database server. They are simply values. An example of executable code that could be inserted is "Drop table [USER];" where the value of a parameter belongs. Oops!
Function getemail() As List(Of String)
Dim SQL As String = "Select EMail FROM [USER]
WHERE EMail Is Not NULL
And MatriculeSalarie Is Not NULL
And [EMail] <> ''
And EtatPaie = 3
And BulletinDematerialise = 1;"
Dim dt As New DataTable
Using con As New SqlConnection("Your connection string"),
cmd As New SqlCommand(SQL, con)
con.Open()
Using reader = cmd.ExecuteReader
dt.Load(reader)
End Using
End Using
Dim strMailTo As New List(Of String)
strMailTo = (From row As DataRow In dt.AsEnumerable
Select row.Field(Of String)(0)).ToList
Return strMailTo
End Function
Function getattachment(email As String) As String()
Dim SQL As String = "Select MatriculeSalarie FROM [USER] WHERE [EMail]='" & email & "'"
Dim mat As String
Using con As New SqlConnection(ConStr),
cmd As New SqlCommand(SQL, con)
cmd.Parameters.Add("#email", SqlDbType.VarChar).Value = email
con.Open()
mat = cmd.ExecuteScalar().ToString()
End Using
Dim Dir As String = ConfigurationManager.AppSettings("path1").ToString
'Your original code was fine, no need for searchPattern.
'I added this so you could see if your search pattern was what you expected.
Dim searchPattern = mat.Substring(1) & "*.pdf"
Debug.Print(searchPattern) 'Appears in the Immediate window
Dim file = IO.Directory.GetFiles(Dir, searchPattern)
Return file
End Function