Vb.net Could not save, locked by another user - vb.net

Question

I am having the problem that about when i try to update a picture, and i click save the error message said that "could not save, locked by another user. where error i did? Sometimes I could update, but sometimes not, why?
And I realize that I have to open Access file and close it then will work.
The error line is cmd.ExecuteNonQuery().
Dim con = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source =..\room.accdb")
Dim ms As New MemoryStream
Dim arrimg As Byte()
Me.PictureBox1.Image.Save(ms, Imaging.ImageFormat.Png)
arrimg = ms.GetBuffer()
ms.Read(arrimg, 0, ms.Length)
Dim sql As String = "UPDATE Userss SET profilepicture =#profilepicture WHERE studentid=" & Form1.txtStuID.Text & ";"
Dim cmd As New OleDbCommand
con.open()
cmd = New OleDbCommand(sql, con)
Dim photo As OleDbParameter = New OleDbParameter("#profilepicture", SqlDbType.Image)
photo.Value = arrimg
cmd.Parameters.Add(photo)
cmd.ExecuteNonQuery()
MessageBox.Show("Profile picture saved.")
con.close()

Answer 1

The 'locked by another user' is a vague message by MS Access since it can be due to a couple of different reasons. It's not to be confused by a specific reason (such as always meaning a table lock). It can be that or it can be the *.ldb file itself or it can be form/table design or even permissions related. However, in your scenario, you are getting it since you have opened the db on MS Access as you mentioned. Opening the db / tables, usually put a lock on the tables.
When you open a record or the form (or table structure) is not designed optimally or someone opens the mdb/accdb who doesn't have both read and write permissions to the folder and file. This error has to do with the *.ldb file associated with the *.mdb/accdb file which is actually what is 'locking' and causing the error.
Some options can be considered, like;
using a NO LOCK in your update statement, but that might not be the best one.
make sure all your connections are well disposed after use.
use using blocks for your objects that implement IDisposable.
you can also read a bit about DEADLOCKS, it might help avoid locks

Answer 2

This should work:
Dim arrimg As Byte()
Using ms As New MemoryStream
Me.PictureBox1.Image.Save(ms, Imaging.ImageFormat.Png)
arrimg = ms.GetBuffer()
ms.Read(arrimg, 0, ms.Length)
End Using
Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source =..\room.accdb")
con.Open()
Using cmd As New OleDbCommand("UPDATE Userss SET profilepicture = #profilepicture WHERE studentid = #studentId;", con)
Dim studentID As New OleDbParameter("#studentId", Form1.txtStuID.Text)
cmd.Parameters.Add(studentID)
Dim photo As New OleDbParameter("#profilepicture", SqlDbType.Image)
photo.Value = arrimg
cmd.Parameters.Add(photo)
cmd.ExecuteNonQuery()
MessageBox.Show("Profile picture saved.")
End Using
con.Close()
End Using
From the code i can see you mix presentation and data access logic, you should probably limit each of your feature to DAL methods so it's easier to find where your DB connection stay open.
With Using like this you can easily avoid to manually dispose the objects and you can be sure the connection will be closed even with exceptions.
Always use parameters and check for disposable object (like MemoryStream).