Save and Fill Data in a ComboBox in C# and SQL Server

In this tutorial, I will show you how to save and fill data in the ComboBox in C# and SQL Server 2005. This method is use for displaying data in the database to the list control of a ComboBox. This process has the capability to control whatever data you want to place into the ComboBox.

To start with:

Create a database and name it “categorydb”.

After creating the database, open Microsoft Visual Studio and create new Windows Form Application. Then do the following design of a Form as shown below.

Go to the Solution Explorer, double click the “View Code”  to display the code editor.

Note: Put using System.Data.SqlClient; above the namespace to access sql server library.

In the code editor, declare all the classes and variables that are needed.

 //initialize all classes
 SqlConnection con = new SqlConnection();
 SqlCommand cmd = new SqlCommand();
 SqlDataAdapter da = new SqlDataAdapter();
 DataTable dt = new DataTable();
 //Declare a variable
 string query;
 int result;

After declaring the classes and variables, establish a connection between SQL server to C#.net in the first load of the Form.

private void Form1_Load(object sender, EventArgs e)
 {
 //connection between sql server to c#
 con.ConnectionString = "Data Source=.\\SQLEXPRESS;Database=cruddb;trusted_connection=true;";
 }

After that, create a method for filling data into a ComboBox from the database.

private void fillCBO()
 {
 try
 {
 //create a query for retrieving data in the database.
 query = "SELECT * FROM tblcategory";
 //initialize new Sql commands
 cmd = new SqlCommand();
 //hold the data to be executed.
 cmd.Connection = con;
 cmd.CommandText = query;
 //initialize new Sql data adapter
 da = new SqlDataAdapter();
 //fetching query in the database.
 da.SelectCommand = cmd;
 //initialize new datatable
 dt = new DataTable();
 //refreshes the rows in specified range in the datasource. 
 da.Fill(dt);
 //Get and set the data source of a comboBox
 comboBox1.DataSource = dt;
 //set the field of a table to display in the list control of a combo box
 comboBox1.DisplayMember = "Category";
 //Display first in the list control
 comboBox1.Text = "Select";

 
 }
 catch (Exception ex)
 {
 MessageBox.Show(ex.Message);
 }
 finally
 {
 da.Dispose();
 }
 }

Go back to the design view, double click the button and do the following codes for saving data in the SQL database.

 private void button1_Click(object sender, EventArgs e)
 {
 try
 {
 //opening connection
 con.Open();
 //create an insert query;
 query = "INSERT INTO tblcategory (Category) VALUES('" + txtcategory.Text + "')"; 
 //it holds the data to be executed.
 cmd.Connection = con;
 cmd.CommandText = query;
 //execute the data.
 int result = cmd.ExecuteNonQuery();
 //validate the result of the executed query.
 if (result > 0)
 {
 MessageBox.Show("Data has been saved in the SQL database");
 //Call a method for filling data into the comboBox.
 fillCBO();
 //clearing textbox
 txtcategory.Clear();
 }
 else
 {
 MessageBox.Show("SQL QUERY ERROR");
 }
 //closing connection
 con.Close();

 }
 catch (Exception ex)//catch exeption
 {
 //displaying error message.
 MessageBox.Show(ex.Message);
 }
 }

Output:

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