DropDownList Data Items Shared With All Web Users? - asp.net

Question

I'm designing a custom ASP.NET drop down list for a Web application to display a list of a lot of organizations.
Btw: I reviewed every other SO question related to dynamically creating a drop-down-list and I couldn't find an answer.
Since there's a lot of organizations I want to build the item list as fast as possible.
Here's my ideas:
I'd share the list like this:
Imports System.Web.UI.WebControls
Public Class Organizations
Inherits DropDownList
Private Shared m_Organizations As List(Of Organization) = Nothing
Public Sub CreateChildControls()
' If list not populated get list from database.
If m_Organizations Is Nothing Then
m_Organizations = Get_Organizations()
End If
For Each Org As Organization in Organizations
Item_Obj = New ListItem(Org.Name, Org.OrgId)
Items.Add(Item_Obj)
Next
MyBase.CreateChildControls()
End Sub
End Class
I did a test. I created a single web page with two copies the drop down list. I ran the web page.
On initial startup of the web page I see m_Organization Is Nothing and Get_Organizations is called.
When I select an organization I see m_Organizations IsNot Nothing so Get_Organizations is not called. That's what I wanted.
When I click on a Submit button on the test page I see m_Organizations IsNot Nothing so Get_Organizations is not called. That's what I wanted.
So Organizations is persisted across page postbacks.
Now my question.
Suppose 3 users are using the web application at the same time and they display the web page with the Organizations drop down list.
Will m_Organizations be shared with all three web applications so it is loaded only once for all three users?
Or, is each user in their own process and therefore GET_Organizations will be called a total of three times?
Thanks, Ed

Answer 1

Each user has their own web page, controls, and code values. They each get their own code copy and their code runs just FOR each user.
So, to load up the dropdown list? It not clear why you pulling into a list?
The base .net objects such as row, and dateable run a lot faster then lists. And these base types can be directly binded to the drop down list (no need for a loop).
So, your on load would be something like:
So, in page load event, you have this:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If IsPostBack = False Then
Me.Instutions.DataSource = Myrst("select ID,Institution from Institutions")
Me.Instutions.DataBind()
End If
End Sub
So, only on the page load do we fill up the combobox (drop down list). You check the "isPostback" value.
Now it possible that you using datasets (or the newer EF) for the data. But even in that case, you can get/grab the data table from that, and shove it directly into the dropdown list data source. You as a general rule will NOT run loops to fill these types of controls (gridview, listview, dropdownlist). They can be bound directly to the result of the data source without loops. And since each users will get their own copy of the data, and your code runs for each user? Then you do want to avoid things like loops - since that code will run separate for each user and each page post back.
So yes, each user gets their own web page, gets their own variables, and runs their own code 100% separate from each user. And that includes a copy of the datasets you have.
When the user selects a value from the drop down list? (yes, we have auto postback = true), and thus the code for that wlll look like:
Protected Sub Instutions_SelectedIndexChanged(sender As Object,
e As EventArgs) Handles Instutions.SelectedIndexChanged
' pk id from drop list = Instutions.SelectedValue
' text value from drop list = Instutions.DataTextField
End Sub
So, it only takes two lines of code to load up the dropdown list - even when you don't have a dataset, or are using EF.
Now, I did use a helper routine called myrst(), and it can be used to fill dropdown lists, datagrids, listviews etc. and once again only two lines of code, and no looping.
that "handy" routine is this:
Public Function Myrst(strSQL As String) As DataTable
Dim mycon As New SqlConnection(My.Settings.Test4)
Dim oReader As New SqlDataAdapter
Dim rstData As New DataTable
oReader.SelectCommand = New SqlCommand(strSQL, mycon)
Try
oReader.Fill(rstData)
Return rstData
Catch
Debug.Print(Err.Description)
Return Nothing
End Try
End Function
So when they select a value in the drop down list? You do get a full page post back, and your on-load event will run. And yes, EACH user has their own web page, and own copy of that code running - they are not relegated to each other in ANY way, and all local, global variables and code is run 100% in a separate session for each user. And each user also has their own Session() variables - and again they are 100% separate and not shared between all users.
So yes, all 3 users will each call and each load up their own copy of that data. (yes, it called 3 times). if that was not the case, then what would occur if you wanted to filter only companies or records belonging to the one user? so you can consider all code and even loading of data a 100% separate thing/concept and process for each user.