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What is the best way to populate comboBox from database

Posted on 2010-08-27
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Last Modified: 2013-12-17
Hi,

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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Question by:dekempeneer
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12 Comments
 
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Expert Comment

by:Dhaest
ID: 33540798
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...
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Author Comment

by:dekempeneer
ID: 33540819
It is a list of all the contacts of everybody and they are sorted by alphabet
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LVL 53

Expert Comment

by:Dhaest
ID: 33540820
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Expert Comment

by:Dhaest
ID: 33540833
>> 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
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Author Comment

by:dekempeneer
ID: 33540844
and how can I do this if I would choose this ?
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Author Comment

by:dekempeneer
ID: 33540903
by the way that asynchronous is for .net 2.0, is there not a better easier way in 4.0 already ? :)
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Expert Comment

by:Dhaest
ID: 33540923
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);

    conn.Open();

    using (OleDbDataReader reader = cmd.ExecuteReader())

    {

      while (reader.Read())

      {

        comboBox1.Items.Add(reader["LastName"].ToString());

      }

    }



  }



}

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Accepted Solution

by:
SriVaddadi earned 500 total points
ID: 33541376

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
http://msdn.microsoft.com/en-us/library/dd997371.aspx

NOTE: It may not be a good idea to search on text fields using "Like" operator.
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Expert Comment

by:ToddBeaulieu
ID: 33545317
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.
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Expert Comment

by:systan
ID: 33550154
>>I found this as answer on the net :
>>You can show the form, but disable the combos.
Use this when your form loads
comboBox1.BeginUpdate();

>>and enable them once the data are ready.
Use this after your data is complete
comboBox1.EndUpdate();  


If you want it asynchronously;
Use
comboBox1.BeginInvoke
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Expert Comment

by:systan
ID: 33550405
OR with background worker
http://www.codeguru.com/forum/showthread.php?t=433482

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

comboBox1.BeginUpdate();

comboBox2.BeginUpdate();

comboBox3.BeginUpdate();

-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-





comboBox1.EndUpdate();

comboBox2.EndUpdate();

comboBox3.EndUpdate();

-do next down-





Note:

//use Datatable for SMALL memory consumption

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LVL 14

Expert Comment

by:systan
ID: 33550419
OPs,
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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