C# How to eliminate duplicate values from comboBox?

Question

I would like to eliminate duplicates from OleDbDataReader Should be easy but I'm spinning my wheels. Any help would be appreciated!

        private void Database_Load(object sender, EventArgs e)
        {         
            try
            {
                connection.Open();
                OleDbCommand command = new OleDbCommand();
                command.Connection = connection;
                string query = "select * from PPAPdatabase";
                command.CommandText = query;                

                OleDbDataAdapter da = new OleDbDataAdapter(command);
                dt = new DataTable();
                da.Fill(dt);
                dataGridView1.DataSource = dt;

                OleDbDataReader reader = command.ExecuteReader();
                while (reader.Read())
            {
                comboBox_Owner.Items.Add(reader["Owner"].ToString());                   
            }

I'd use the database to do that for you. Just write a suitable select distinct query for it. You could do it in code using LINQ, but there's no point in this example. e.g. `select distinct Owner from PPAPdatabase where Owner is not null` — ManoDestra, May 05 '16 at 17:54
Clear the ComboBox first near the top of your method using `comboBox_Owner.Items.Clear()`, then amend your SQL to be `select distinct Owner from PPAPdatabase where Owner is not null`. And you only need to fill the datasource once, you don't really require to do the reader as well. Use either the reader or the datasource method. Job done :) — ManoDestra, May 05 '16 at 18:26

CodeNotFound · Accepted Answer · 2016-05-05T18:20:59.920

3

Refactor your SQL query like this :

select distinct Owner from PPAPdatabase

Instead of

select * from PPAPdatabase

The only column you need in your code is Owner then get that only one column and apply DISTINCT clause to it to get distinct value for that column.

Or replace the following lines :

OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
    comboBox_Owner.Items.Add(reader["Owner"].ToString());                   
}

By this :

var owners = dt.AsEnumerable().Select(row => row["Owner"].ToString()).Distinct();
foreach(var owner in owners)
{
    comboBox_Owner.Items.Add(owner);                   
}

In this solution we're using one SQL Query to your Database and reuse the result to extreact distinct owners.

edited May 05 '16 at 18:20

answered May 05 '16 at 17:54

CodeNotFound

22,153
10
68
69

Correct me I am wrong but I used **string query = "select * from PPAPdatabase";** to show all data in datagridview. – NOGRP90 May 05 '16 at 18:06
@NOGRP90 Then you might create separate command. Each command has its own SQL query. – CodeNotFound May 05 '16 at 18:10
@CodeNotFound Could you please write it? – NOGRP90 May 05 '16 at 18:14
@adjan Clear the combobox prior to population from the database, of course. – ManoDestra May 05 '16 at 18:18
1

@NOGRP90 I updated my answer then for another better way. – CodeNotFound May 05 '16 at 18:21
@CodeNotFound Thank you so much! – NOGRP90 May 05 '16 at 18:26
@NOGRP90 If it works then you must accept it as an answer I Think :) – CodeNotFound May 05 '16 at 18:27
@CodeNotFound Can I use "var owners =..." more time for another combobox? Just replace the owners. – NOGRP90 May 05 '16 at 18:28
Then you must declare the local variable `owners` as a field of your class. – CodeNotFound May 05 '16 at 18:30
For example: I have a **"comboBox_Pline"** and another 2 textbox. Could you please show me how to do that? I am newbie in programming. I would really appreciate. – NOGRP90 May 05 '16 at 18:33
You will do the same foreach instruction that you do with your comboBox_Owner combobox. – CodeNotFound May 05 '16 at 18:35
If `owners` if a field on your class. Just od this `foreach(var owner in this.owners) { comboBox_Pline.Items.Add(owner); }` – CodeNotFound May 05 '16 at 18:36
@CodeNotFound You look proficient. Are you able to solve my another question?? :)) http://stackoverflow.com/questions/37048713/c-sharp-how-to-store-selected-checkedlistbox-values-in-different-columns-in-ms – NOGRP90 May 05 '16 at 18:54

score 2 · Answer 2 · answered May 05 '16 at 17:57

2

you can do this way

while (reader.Read())
{
    if (!comboBox_Owner.Items.Contains(reader["Owner"].ToString()))
        comboBox_Owner.Items.Add(reader["Owner"].ToString());                  
}

answered May 05 '16 at 17:57

Mostafiz

7,243
3
28
42

It would be better to clear the combobox and populate it from distinct values from the database, as suggested in other answers. That's the correct solution for you. – ManoDestra May 05 '16 at 18:20
@ManoDestra Yes. It would be but I don't know how to do that :) – NOGRP90 May 05 '16 at 18:23
I've added the technique as a comment to the question itself. – ManoDestra May 05 '16 at 18:28

C# How to eliminate duplicate values from comboBox?

2 Answers2