How to add values of combobox to database?

Question

In the collection of my BloodType combobox property. I have 3 values which is O, A and C. But after I choose the option of the value I want, and click submit I get this error.

The parameterized query '(@pFirstName nvarchar(5),@pLastName nvarchar(6),@pContact nvarch' expects the parameter '@pBloodType', which was not supplied.

It will worked if I use a textbox for my bloodtype instead.

For my textbox code which is before.

updateCmd.Parameters.AddWithValue("@pBloodType", txtpBloodType.Text);

For comboBox code which i am using now.

updateCmd.Parameters.AddWithValue("@pBloodType", cbpBloodType.SelectedValue);

Still Object reference not set to an instance of an object.

   public patient()
    {
        InitializeComponent();
        this.cbpBloodType = new System.Windows.Forms.ComboBox();
        this.cbpBloodType.Items.Add("O");
        this.cbpBloodType.Items.Add("A");
        this.cbpBloodType.Items.Add("C");
    }

    private int AddPatientRecord()
    {
        int result = 0;
        // TO DO: Codes to insert customer record
        //retrieve connection information info from App.config
        string strConnectionString = ConfigurationManager.ConnectionStrings["SACPConnection"].ConnectionString;
        //STEP 1: Create connection
        SqlConnection myConnect = new SqlConnection(strConnectionString);
        //STEP 2: Create command
        String strCommandText = "INSERT PATIENT(pFirstName, pLastName, pContact, pAddress, pCity, pZip, pNationality, pRace, pIC, pGender, pDOB, pBloodType, pEmail) "
            + " VALUES (@pFirstName,@pLastName,@pContact,@pAddress,@pCity,@pZip,@pNationality, @pRace, @pIC, @pGender, @pDOB, @pBloodType, @pEmail)";

        SqlCommand updateCmd = new SqlCommand(strCommandText, myConnect);

        updateCmd.Parameters.AddWithValue("@pFirstName", txtpFirstName.Text);
        updateCmd.Parameters.AddWithValue("@pLastName", txtpLastName.Text);
        //updateCmd.Parameters["@clientid"].Direction = ParameterDirection.Output; 
        updateCmd.Parameters.AddWithValue("@pContact", txtpContact.Text);
        updateCmd.Parameters.AddWithValue("@pAddress", txtpAddress.Text);
        updateCmd.Parameters.AddWithValue("@pCity", txtpCity.Text);
        updateCmd.Parameters.AddWithValue("@pZip", txtpZip.Text);
        updateCmd.Parameters.AddWithValue("@pNationality", txtpNationality.Text);
        updateCmd.Parameters.AddWithValue("@pRace", txtpRace.Text);
        updateCmd.Parameters.AddWithValue("@pIC", txtpIC.Text);
        if (rbMale.Checked)
        {
            updateCmd.Parameters.AddWithValue("@pGender", "M");
        }
        else
        {
            updateCmd.Parameters.AddWithValue("@pGender", "F");
        }
        updateCmd.Parameters.AddWithValue("@pDOB", dtppDOB.Value);
        string value = cbpBloodType.SelectedItem == null ? "A" : cbpBloodType.SelectedItem.ToString();
        updateCmd.Parameters.AddWithValue("@pBloodType", value);
        updateCmd.Parameters.AddWithValue("@pEmail", txtpEmail.Text);
        // STEP 3 open connection and retrieve data by calling ExecuteReader
        myConnect.Open();
        // STEP 4: execute command
        // indicates number of record updated.
        result = updateCmd.ExecuteNonQuery();

        // STEP 5: Close
        myConnect.Close();
        return result;

    }

Answer 1

Try to initialize your combobox in code behind :

public Form1()
{
    InitializeComponent();
    cb1.Items.Add("O");
    cb1.Items.Add("A");
    cb1.Items.Add("C");
}

Then access the data with cbpBloodType.SelectedItem.ToString();

string value = cbpBloodType.SelectedItem == null ? "A" : cbpBloodType.SelectedItem.ToString();
updateCmd.Parameters.AddWithValue("@pBloodType", value);

Answer 2

Not sure why the null exception but in any case I bet you are getting the wrong value from "Selected Value". Assign the variable first then step through it. I bet you might find you are not getting back "A" or "B" but rather something like "System.Windows.Controls..."

try this and see if you get the same error.

string bloodtype = cbpBloodType.Text;

if(!String.IsNullOrEmpty(bloodtype))

Answer 3

Mybe cbpBloodType.SelectedValue return null. How are you binding your drop downlist ?

Try this

private int AddPatientRecord()
{
    int result = 0;
    // TO DO: Codes to insert customer record
    //retrieve connection information info from App.config
    string strConnectionString = ConfigurationManager.ConnectionStrings["SACPConnection"].ConnectionString;
    //STEP 1: Create connection
    SqlConnection myConnect = new SqlConnection(strConnectionString);
    //STEP 2: Create command
    String strCommandText = "INSERT PATIENT(pFirstName, pLastName, pContact, pAddress, pCity, pZip, pNationality, pRace, pIC, pGender, pDOB, pBloodType, pEmail) "
        + " VALUES (@pFirstName,@pLastName,@pContact,@pAddress,@pCity,@pZip,@pNationality, @pRace, @pIC, @pGender, @pDOB, @pBloodType, @pEmail)";

    SqlCommand updateCmd = new SqlCommand(strCommandText, myConnect);

    updateCmd.Parameters.AddWithValue("@pFirstName", txtpFirstName.Text);
    updateCmd.Parameters.AddWithValue("@pLastName", txtpLastName.Text);
    //updateCmd.Parameters["@clientid"].Direction = ParameterDirection.Output; 
    updateCmd.Parameters.AddWithValue("@pContact", txtpContact.Text);
    updateCmd.Parameters.AddWithValue("@pAddress", txtpAddress.Text);
    updateCmd.Parameters.AddWithValue("@pCity", txtpCity.Text);
    updateCmd.Parameters.AddWithValue("@pZip", txtpZip.Text);
    updateCmd.Parameters.AddWithValue("@pNationality", txtpNationality.Text);
    updateCmd.Parameters.AddWithValue("@pRace", txtpRace.Text);
    updateCmd.Parameters.AddWithValue("@pIC", txtpIC.Text);
    if (rbMale.Checked)
    {
        updateCmd.Parameters.AddWithValue("@pGender", "M");
    }
    else
    {
        updateCmd.Parameters.AddWithValue("@pGender", "F");
    }
    updateCmd.Parameters.AddWithValue("@pDOB", dtppDOB.Value);
    if(!String.IsNullOrEmpty(cbpBloodType.SelectedValue.ToString()))
    {
      updateCmd.Parameters.AddWithValue("@pBloodType", cbpBloodType.SelectedValue.ToString());
    }
    else
    {
       // Pass default value, for example A
       updateCmd.Parameters.AddWithValue("@pBloodType","A");
    } 
    updateCmd.Parameters.AddWithValue("@pEmail", txtpEmail.Text);
    // STEP 3 open connection and retrieve data by calling ExecuteReader
    myConnect.Open();
    // STEP 4: execute command
    // indicates number of record updated.
    result = updateCmd.ExecuteNonQuery();

    // STEP 5: Close
    myConnect.Close();
    return result;

}