Get child page data from master page selectedItems - asp.net

Question

I have location DropdownList in my master page. I have set control in my child page which takes properties from master page. Now I am running a query
SELECT * FROM table where city like '"+city.text+"'
here city.text gets value from master page selected cities. But my problem is it's not actually showing records as per city.text has values in it. It shows any random records.
My Code
Master Page
<asp:DropDownList ID="locationSelector" runat="server" AutoPostBack="true">
<asp:ListItem Selected>Pune</asp:ListItem>
<asp:ListItem>Delhi</asp:ListItem>
<asp:ListItem>Chennai</asp:ListItem>
<asp:ListItem>Bangalore</asp:ListItem>
<asp:ListItem>Mumbai</asp:ListItem>
</asp:DropDownList>
Child page VB Code
Dim location As DropDownList = Page.Master.FindControl("locationSelector")
city.Text = location.SelectedItem.ToString
If Not IsPostBack Then
Try
query = "SELECT * FROM hospitals where city like '" + city.Text + "'"
Dim cmd As New MySqlCommand(query, con)
cmd.CommandTimeout = 120
Dim da As New MySqlDataAdapter(cmd)
Dim table As New DataTable
da.Fill(table)
ViewState("Data") = table
hospitals.DataSource = table
hospitals.DataBind()
Catch ex As Exception
Response.Write(ex)
End Try
End If
UPDATE
Protected Sub hospitals_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
Dim location As DropDownList = Page.Master.FindControl("locationSelector")
city.Text = location.SelectedItem.ToString
End Sub
Sometimes it also throws TimeOut error. But most of the time It gets results but not as per selected items. What will be any other solution for this?

Answer 1

A couple of tips:
1) Timeout errors can happen for a number of reasons, including lots of other traffic to the site, connection pools all used up etc. I would, for a small list of cities, maybe keep that in a cache after the first call, so that you do not need to load the city list from database every time. Depending on your country, if you only have a few thousand cities, then just put it in an in-memory list.
2) You are using a "SELECT *" which is usually not really cool to other developers, nor to your code if the table contains more than just a city name. IF you write Select CityName from Table, then you will effectively have reduced the amount of data going from your database to your program, and it is clear to the other developers exactly what you're pulling from that table.
3) If you have an ID for the city, it will likely perform even better as string matcing is REALLY slow compared to matching a couple of ID's. I've seen 20% speed improvements by replacing strings with constants, you wouldn't believe how slow strings are in code these days.
4) Last, and I think you may already have done this, make sure that you INDEX every field that you do a WHERE filter on. If you search for Hospitals, then make sure that the Hospitals.City field is indexed to avoid row lookups.
I hope (any) of this helps you :)

Answer 2

As per my understanding you need to change below
to fetch the selected TEXT value use location.SelectedItem.Text instead of location.SelectedItem.ToString()
city.Text = location.SelectedItem.Text // change here
before binding the dropdown control check the no. of rows
if(table.Rows.Count>0)
{
hospitals.DataSource = table;
hospitals.DataBind();
}

Answer 3

I would suggest to use prerender event within page. In prerender event try to access your master page control and get value.