Object reference not set to an instance of an object. Please Help to solve error

Question

I am new to C#.

Kindly tell me what`s wrong with this code. I am inserting data in data base using two input fields EndValueTextBox and StartValueTextBox .

I am receiving following error. "Object reference not set to an instance of an object"

private void buttonSave_Click(object sender, EventArgs e)
{
    connection = new System.Data.SqlClient.SqlConnection();
     da = new SqlDataAdapter();
    try
    {
        connection.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename='G:\\C#.Net\\Forms Practice\\WindowsFormsPractice1\\WindowsFormsPractice1\\WindowsFormsPractice1.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True";
    }
    catch (System.Exception ex)
    {
        MessageBox.Show(ex.Message,"Connection String");
    }
    try
    {
        connection.Open();
        string sql = "insert into TBLWORKERS (first_name , last_name )" + " values('" + StartValueTextBox.Text + "', '" + EndValueTextBox.Text + ")";
        //SqlDataAdapter da = new SqlDataAdapter(query, connString);


        da.InsertCommand.CommandText = sql;

        da.InsertCommand.ExecuteNonQuery();

    }
    catch (System.Exception ex)
    {
        MessageBox.Show(ex.Message, "Connection open");
    } 
}

A warning about the way you create your SQL. You're having the security risk of Sql Injection. This means that if someone will enter some sql in one of those texboxes instead of a normal start/end value that sql will be executed against the database (for example a 'drop table' command!) — Wouter de Kort
– Wouter de Kort ♦, Commented Oct 27, 2011 at 5:56
@Wouter: The OP doesn't understand what you mean. How about providing a link to a SQL injection article that describes how to parameterize? — Robert Harvey
– Robert Harvey, Commented Oct 27, 2011 at 5:58
@RobertHarvey you're right :) This link: csharp-station.com/Tutorials/AdoDotNet/Lesson06.aspx has a nice introduction about how to construct a sql query — Wouter de Kort
– Wouter de Kort ♦, Commented Oct 27, 2011 at 6:01
A single try/catch statement will also be sufficient - you don't need multiple. — SliverNinja
– SliverNinja, Commented Oct 27, 2011 at 6:02

SliverNinja · Accepted Answer · 2011-10-27 05:55:16Z

2

Your SqlDataAdapter is never assigned a connection to execute the query on. You need to associate the SqlConnection with the SqlDataAdapter during or after construction.

answered Oct 27, 2011 at 5:55

SliverNinja

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1 Comment

Robert Harvey Over a year ago

If the OP is truly new to C#, this is Greek to him. How about a code sample?

Fischermaen · Accepted Answer · 2011-10-27 05:58:00Z

1

This line da.InsertCommand.CommandText = sql; has to be in that way:

da.InsertCommand = new SqlCommand(sql);

answered Oct 27, 2011 at 5:58

Fischermaen

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1 Comment

Robert Harvey Over a year ago

You can do it the OP's way too, using a string.

Sathyajith Bhat · Accepted Answer · 2011-10-27 06:02:09Z

0

At what point you are the exception? Probably those line

System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection();
SqlDataAdapter da = new SqlDataAdapter();

edited Oct 27, 2011 at 6:02

Sathyajith Bhat

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answered Oct 27, 2011 at 6:00

Carmelo La Monica

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1 Comment

SliverNinja Over a year ago

neither of these lines could be the exception - they are simple ctors.

Damith · Accepted Answer · 2011-10-27 06:10:00Z

0

string connetionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename='G:\\C#.Net\\Forms Practice\\WindowsFormsPractice1\\WindowsFormsPractice1\\WindowsFormsPractice1.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True";

SqlDataAdapter adapter = new SqlDataAdapter();

string sql =  "insert into TBLWORKERS (first_name , last_name )" + " values('" + StartValueTextBox.Text + "', '" + EndValueTextBox.Text + ")";

SqlConnection connection = new SqlConnection(connetionString);
try {
    connection.Open();
    adapter.InsertCommand = new SqlCommand(sql, connection);
    adapter.InsertCommand.ExecuteNonQuery();
} catch (Exception ex) {
    MessageBox.Show(ex.Message);
}

edited Oct 27, 2011 at 6:10

answered Oct 27, 2011 at 5:56

Damith

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Comments

Tim · Accepted Answer · 2011-10-27 06:21:22Z

Here's a minor rewrite of your code (not tested) that should take care of the SqlDataAdapter not having the connection object assigned and also demonstrates how to use parameterized queries to help defend against SQL Injection attacks:

private void buttonSave_Click(object sender, EventArgs e)
{

    try
    {
        // The using block will automatically dispose of your connection when
        // the block is exited and is considered standard practice.
        using (SqlConnection connection = new SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename='G:\\C#.Net\\Forms Practice\\WindowsFormsPractice1\\WindowsFormsPractice1\\WindowsFormsPractice1.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True";))
        {

            SqlDataAdpter da = new SqlDataAdapter();

            connection.Open();

            // Assign the SqlConnection object to the SqlDataAdapter
            da.Connection = connection;

            // Parameterize the query as shown below
            string sql = "INSERT INTO TBLWORKERS(first_name, last_name) VALUES(@first_name, @last_name)";

            da.InsertCommand.CommandText = sql;

            // Add the values for the parameters
            da.InsertCommand.Parameters.Add("@first_name", SqlDbType.NVarChar, 25, StartValueTextBox.Text);
            da.InsertCommand.Parameters.Add("@last_name", SqlDbType.NVarChar, 25, EndValueTextBox.Text);

            // Execute the query - rows will have the number of rows
            // affected.  should be 1 in this case if succesful
            int rows = da.InsertCommand.ExecuteNonQuery();           
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "Connection open");
    }
}

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