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What is the best way to populate comboBox from database


what is the best way to populate comboBox from database.. the reason I
am asking is that i have more than 8 comboBoxes in one form and each
should retrieve  a lot of data (one combobox contains 50000 items) from a table and I don't want that to slow the form down.

I found this as answer on the net :
You can show the form, but disable the combos. After that, launch an async
delegate populating the combos, and enable them once the data are ready.

But I have no idea on how to do this, can you please submit a sample code...
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1 Solution
I don't see any reason to load such a huge combobox: 50.000 items ? I don't want to be the user that open the combobox and search for my item he/she needs ...

 I would suggest that you implement a master/detail combo box wherein the user will first select a category (master) then once a selection has been made, populate another combo box (detail) for the items for the selected category...
dekempeneerAuthor Commented:
It is a list of all the contacts of everybody and they are sorted by alphabet
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>> It is a list of all the contacts of everybody and they are sorted by alphabet

You can for example also use some kind of search, where the user first enters 3 or 4 characters of a name, that triggers a search a database and with this results the first 50 (or 100) will be filled into a dropdown
dekempeneerAuthor Commented:
and how can I do this if I would choose this ?
dekempeneerAuthor Commented:
by the way that asynchronous is for .net 2.0, is there not a better easier way in 4.0 already ? :)
Very easily: add a textbox and a button on the screen. Behind this button, you perform a query and load the data into the combobox.

Example below for an access-database
string connString = "Microsoft.Jet.OLEDB.4.0;Data Source=C:\\bd1.mdb"; 
string SqlString = "Select top 50 LastName From Contacts Where LastName like '?*'";
using (OleDbConnection conn = new OleDbConnection(ConnString))
  using (OleDbCommand cmd = new OleDbCommand(SqlString, conn))
    cmd.CommandType = CommandType.Text;
    cmd.Parameters.AddWithValue("LastName", txtLastName.Text);
    using (OleDbDataReader reader = cmd.ExecuteReader())
      while (reader.Read())



Open in new window


You might want to implement producer-consumer pattern where the producer would produce the data and consumer would consume it and populate your combo.

Here is a link which might help

NOTE: It may not be a good idea to search on text fields using "Like" operator.
I'd still be concerned about performance. I agree with dhaest on this. Most UI controls get REALLY SLOW when you add such large numbers of items. Also, the thumb would be really small with that many items. A simple filter would make it so much better. A textbox to allow the user to enter a partial name would go a long way in making it more usable. When something is entered, re-issue the query, wrap the results in a new collection and bind the combo to it.
>>I found this as answer on the net :
>>You can show the form, but disable the combos.
Use this when your form loads

>>and enable them once the data are ready.
Use this after your data is complete

If you want it asynchronously;
OR with background worker

OR with this for simple psudo code;
//Global Declaration
SqlDataAdapter da1 = new MySqlDataAdapter();
SqlDataAdapter da2 = new MySqlDataAdapter();
SqlDataAdapter da3 = new MySqlDataAdapter();
SqlDataAdapter da4 = new MySqlDataAdapter();
SqlDataAdapter da5 = new MySqlDataAdapter();
SqlDataAdapter da6 = new MySqlDataAdapter();
SqlDataAdapter da7 = new MySqlDataAdapter();
SqlDataAdapter da8 = new MySqlDataAdapter();

//During Form LOAD
string s1 = "select  f1 from t1";
da1.SelectCommand = new SqlCommand(s1, YOURsqlconnection);
string s2 = "select  f1 from t2";
da2.SelectCommand = new SqlCommand(s2, YOURsqlconnection);
string s3 = "select  f1 from t3";
da3.SelectCommand = new SqlCommand(s3, YOURsqlconnection);
string s4 = "select  f1 from t4";
da4.SelectCommand = new SqlCommand(s4, YOURsqlconnection);
string s5 = "select  f1 from t5";
da5.SelectCommand = new SqlCommand(s5, YOURsqlconnection);
string s6 = "select  f1 from t6";
da6.SelectCommand = new SqlCommand(s6, YOURsqlconnection);
string s7 = "select  f1 from t7";
da7.SelectCommand = new SqlCommand(s7, YOURsqlconnection);
string s8 = "select  f1 from t8";
da8.SelectCommand = new SqlCommand(s8, YOURsqlconnection);
DataTable dt1 = new DataTable();
da1.Fill (dt1);
DataTable dt2 = new DataTable();
da2.Fill (dt2);
DataTable dt3 = new DataTable();
da3.Fill (dt3);
DataTable dt4 = new DataTable();
da4.Fill (dt4);
DataTable dt5 = new DataTable();
da5.Fill (dt5);
DataTable dt6 = new DataTable();
da6.Fill (dt6);
DataTable dt7 = new DataTable();
da7.Fill (dt7);
DataTable dt8 = new DataTable();
da8.Fill (dt8);

//During Form SHOWN / or button click
-do next down-

comboBox1.DisplayMember = "f1";
comboBox2.DisplayMember = "f1";
comboBox3.DisplayMember = "f1";
-do next down-

comboBox1.DataSource = dt1;
comboBox2.DataSource = dt2;
comboBox3.DataSource = dt3;
-do next down-

-do next down-

//use Datatable for SMALL memory consumption

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correction; for my second comment.

for MS sql
SqlDataAdapter da1 = new SqlDataAdapter();

for mYsql
MySqlDataAdapter da1 = new MySqlDataAdapter();

for ado
OLEDBlDataAdapter da1 = new OLEDBDataAdapter();

for odbc
ODbCDataAdapter da1 = new ODbcDataAdapter();

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