Object reference not set to an instance of an object.

balanjingot

hi, what would be the probable cause why i received this kind of error message... this is my code: try { foreach(DataGridViewRow row in dataGridView4.Rows) { long itemcode = 0; string description = ""; int quantity = 0; string unit = ""; itemcode = Convert.ToInt64(row.Cells[0].Value); description = row.Cells[1].Value.ToString(); quantity = Convert.ToInt32(row.Cells[2].Value); unit = row.Cells[3].Value.ToString(); String query = "INSERT INTO test(itemcode,description,quantity,unit) VALUES (itemcode,description,quantity,unit)"; MySqlCommand command = new MySqlCommand(query, connection); command.ExecuteNonQuery(); } } catch (MySqlException mse) { MessageBox.Show(mse.Message); } }

jing

lost in transition

Where is the debugger popping the error out. What line?

God Bless, Jason

DavidCrow wrote:

It would not affect me or my family one iota. My wife and I are in charge of when the tv is on, and what it displays. I do not need any external input for that.

PIEBALDconsult

Some value is null. Try debugging to see what line throws the exception. If you still can't figure it out, then post more information.

balanjingot

hi, thanks for the reply... the following lines: description = row.Cells[1].Value.ToString(); unit = row.Cells[3].Value.ToString(); these two lines of code are string, i wonder why it has an error. pls. help:) thanks,

jing

balanjingot

hi, thanks for the reply.. the following 2 lines received the error message.. description = row.Cells[1].Value.ToString(); unit = row.Cells[3].Value.ToString(); regard:-D

jing

lost in transition

Like PIEBALDconsult said below, You need to use the debugger to find out what line.

God Bless, Jason

DavidCrow wrote:

It would not affect me or my family one iota. My wife and I are in charge of when the tv is on, and what it displays. I do not need any external input for that.

balanjingot

hi, ok thanks a lot... God Bless:)

jing

lmoelleb

Then either row, row.Cells, row.Cells[1], or row.Cells[1].Value is null. The debugger will show the value of each of them so it should be easy to find.

balanjingot

hi, by the way will you please help me on how to insert values from the datagridview to the database table? waiting for your reply:)

jing

balanjingot

hi, thanks.. yap,through the debugger,i've found out that row.Cell[1].Value is null.i'm trying to fix it right now... :)

jing

PIEBALDconsult

In your String query = "INSERT INTO test(itemcode,description,quantity,unit) VALUES (itemcode,description,quantity,unit)"; You'll want to use parameters for itemcode,description,quantity,unit I'm not as familiar with MySql, but in Sql Server I'd prefix each with an @ @itemcode,@description,@quantity,@unit Then instantiate a MySqlParameter for each and add them to the command's parameter collection. Roughly: command.Parameters.Add ( new MySqlParameter ( "@itemcode" , itemcode ) ; But if you're going to be inserting a bunch of data in a loop, you'll want something like: command.Parameters.Add ( new MySqlParameter ( "@itemcode" , typeof(itemcode) ) ; then in the loop: command.Parameters [ "@itemcode" ].Value = itemcode ; (will that work?)

PIEBALDconsult

This is untested, and I don't usually use DataGridViews or MySql:

try
{
connection.Open() ;

MySqlCommand command = new MySqlCommand
(
    "INSERT INTO test(itemcode,description,quantity,unit) VALUES (@itemcode,@description,@quantity,@unit)"
, 
    connection
) ;

foreach ( DataGridViewColumn col in dataGridView4.Columns )
{
    command.Parameters.Add ( new MySqlParameter ( "@" + col.DataPropertyName , col.ValueType ) ;
}

command.Transaction = connection.BeginTransaction() ;

foreach(DataGridViewRow row in dataGridView4.Rows)
{
    foreach ( DataGridViewCell cel in row.Cells )
    {
        command.Parameters \[ "@" + cel.DataPropertyName \].Value = cel.Value ;
    }

    command.ExecuteNonQuery() ;
}

command.Transaction.Commit ;

}
catch ( MySqlException mse )
{
command.Transaction.Rollback ;
MessageBox.Show ( mse.Message ) ;
}
finally
{
connection.Close() ;
}

PIEBALDconsult

P.S. Using the technique above you can write a library routine that will even create the SQL statement, and you could simply pass it a reference to any DataGridView and the name of the table into which to sert the data, and never (hardly ever) write an INSERT statement again: InsertData ( "test" , dataGridView4 ) ;

Rob Graham

balanjingot wrote:

String query = "INSERT INTO test(itemcode,description,quantity,unit) VALUES (itemcode,description,quantity,unit)";

Won't work. C# isn't going to magically convert the variable names in th VALUES clause to the appropriate things. Best approach would be to make the list in the VALUES clause use parameters. "INSERT INTO test(itemcode,description,quantity,unit) VALUES ( @itemcode,@description,@quantity,@unit)" //What is a MySqlCommand? System.Data.SqlCommand is a sealed class, so you can't derive from it... MySqlCommand command = new MySqlCommand(query, connection); command.Parameters.Add( new SqlParameter("@itemcode",itemcode); ... the rest, in order... command.ExecuteNonQuery(); I would suppose that one other likely cause is that your MySqlCommand Class is flawed, and the constructor silently fails...

balanjingot

hi, ok, it try to get the logic of your program so I could migrate it to MySql... regards:)

jing

balanjingot

hi everybody, thanks for your reply and suggestions, finally i got the solution to my problem... my revised code: private void button13_Click(object sender, EventArgs e) { try { for (int i = 0; i < dataGridView4.Rows.Count -1; i++) { DataGridViewRow row = dataGridView4.Rows[i]; long itemcode = 0; string description = ""; int quantity = 0; string unit = ""; itemcode = Convert.ToInt64(row.Cells[0].Value); if (description != null) { description = row.Cells[1].Value.ToString() + ""; } quantity = Convert.ToInt32(row.Cells[2].Value); unit = row.Cells[3].Value.ToString(); String query = "INSERT INTO test(itemcode,description,quantity,unit) VALUES (" + " " + itemcode + " ,'" + description + "'" + " , " + quantity + " ,'" + unit + "'" + " )"; MySqlCommand command = new MySqlCommand(query, connection); MessageBox.Show(command.ExecuteNonQuery().ToString()); } } thanks guys regards:)

jing

AFSEKI

Check if row.Cells[X].Value is null or DBnull before converting or ToString()ing them 2) Catch also (Exception ex) and System.Diagnostics.Debug.WriteLine("Error! Source: ", ex.Source + ", Message: " + ex.Message); to see what happened. You can also do this: if(ex.InnerException != null) System.Diagnostics.Debug.WriteLine(ex.InnerException.Source + ", " + ex.innerException.Message); Hope this helps...

balanjingot

hi, thanks, my program already worked out!! regards:)

jing