Develop Reference

C# - Update SQL Table

I want to update my sql table. I was searching here and found solutions on how to go onto that problem. But sadly it just wont update the database. I have no clue what the problem is.
I checked to sql command a couple of times for writing mistakes but couldnt find any or fixed them but still sadly nothing. I suppose it's something within the try block but cant find it out.
This is my code:
string connetionString = null;
SqlConnection connection;
SqlCommand command;
string sql = null;
SqlDataReader dataReader;
connetionString = "Data Source=xxx\\xxx;Initial Catalog=xxx;User ID=xxx;Password=xxx";
sql = "UPDATE Employees SET LastName = '" + Lnamestring + "', FirstName = '" + Fnamestring + "', Title = '" + Titelstring + "', TitleOfCourtesy = '" + ToCstring + "', BirthDate = '" + Birthdatestring + "', HireDate = '" + Hiredatestring + "', Address = '" + Adressstring + "', City = '" + Citystring + "', Region = '" + Regionstring + "', PostalCode = '" + Postalstring + "', Country = '" + Countrystring + "', HomePhone = '" + Phonestring + "', Extension = '" + Extensionsstring + "', Notes = '" + Notesstring + "', ReportsTo = '" + ReportTostring + "' WHERE EmployeeID = '" + IDstring + "'; ";
connection = new SqlConnection(connetionString);
try
{
connection.Open();
command = new SqlCommand(sql, connection);
SqlDataAdapter sqlDataAdap = new SqlDataAdapter(command);
command.Dispose();
connection.Close();
MessageBox.Show("workd ! ");
}
catch (Exception ex)
{
MessageBox.Show("Can not open connection ! ");
}
I hope someone can help me find my mistake.
EDIT: when i try it out it seems to work as the windows pops up with "workd" but the database is unchanged.

As Michał Turczyn wrote in his answer, you have some problems with your code.
I agree with everything he wrote, but I thought you might benefit from seeing how your code should look like - so here you go:
var connetionString = "Data Source=EVOPC18\\PMSMART;Initial Catalog=NORTHWND;User ID=test;Password=test";
var sql = "UPDATE Employees SET LastName = #LastName, FirstName = #FirstName, Title = #Title ... ";// repeat for all variables
try
{
using(var connection = new SqlConnection(connetionString))
{
using(var command = new SqlCommand(sql, connection))
{
command.Parameters.Add("#LastName", SqlDbType.NVarChar).Value = Lnamestring;
command.Parameters.Add("#FirstName", SqlDbType.NVarChar).Value = Fnamestring;
command.Parameters.Add("#Title", SqlDbType.NVarChar).Value = Titelstring;
// repeat for all variables....
connection.Open();
command.ExecuteNonQuery();
}
}
}
catch (Exception e)
{
MessageBox.Show($"Failed to update. Error message: {e.Message}");
}

Few issues with your code:
1) Use using, when working with IDisposable objects, in your case connection and command.
2) As suggested in comments, use SqlCommandParameters instead of concatenating strings for security reasons (google "preventing from SQL injections")
3) You don't execute your query! How you want it to make an impact if you don't do it? There's, for example, method like ExecuteNonQuery in SqlCommand class.

string connetionString = null;
SqlConnection connection;
SqlCommand command;
string sql = null;
SqlDataReader dataReader;
connetionString = "Data Source=EVOPC18\\PMSMART;Initial Catalog=NORTHWND;User ID=test;Password=test";
sql = "UPDATE Employees SET LastName = '" + Lnamestring + "', FirstName = '" + Fnamestring + "', Title = '" + Titelstring + "', TitleOfCourtesy = '" + ToCstring + "', BirthDate = '" + Birthdatestring + "', HireDate = '" + Hiredatestring + "', Address = '" + Adressstring + "', City = '" + Citystring + "', Region = '" + Regionstring + "', PostalCode = '" + Postalstring + "', Country = '" + Countrystring + "', HomePhone = '" + Phonestring + "', Extension = '" + Extensionsstring + "', Notes = '" + Notesstring + "', ReportsTo = '" + ReportTostring + "' WHERE EmployeeID = '" + IDstring + "'; ";
connection = new SqlConnection(connetionString);
try
{
connection.Open();
command = new SqlCommand(sql, connection);
SqlDataAdapter sqlDataAdap = new SqlDataAdapter(command);
command.ExecuteNonQuery();
command.Dispose();
connection.Close();
MessageBox.Show("workd ! ");
}
catch (Exception ex)
{
MessageBox.Show("Can not open connection ! ");
}
Don't forget to execute the command
Try to get the stacktrace or error message from Exception as much as possible. For example: MessageBox.Show($"Can not open connection ! {e.GetBaseException().Message}, {e.StackTrace}");

SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandText = "update CarTb1 set ( #RegNo , #MOdel , #Price , #Available where #Brand);";
cmd.CommandType = System.Data.CommandType.Text;
Da = new SqlDataAdapter("Select * From CarTb1", con);
Da.Fill(Dt);
cmd.Parameters.AddWithValue("#RegNo", txtRegnumber.Text);
cmd.Parameters.AddWithValue("#Brand", combBrand.Text);
cmd.Parameters.AddWithValue("#Model", txtModel.Text);
cmd.Parameters.AddWithValue("#Price", txtPrice.Text);
cmd.Parameters.AddWithValue("#Color", txtColor.Text);
cmd.Parameters.AddWithValue("#Available", combAvailable.Text);
con.Open();
cmd.ExecuteNonQuery();
MessageBox.Show("Record Edited Successfally");
con.Close();
ClearData();

Please use the ExecuteNonQuery() instead of SqlDataAdapter:
connection.Open();
command = new SqlCommand(sql, connection);
command.ExecuteNonQuery();
command.Dispose();
connection.Close();
MessageBox.Show("workd ! ");

Different language in DataGridView

I am working on a C# project. I have created a dataset by use of sql server and I tried to show the data in DataGridView table. Then I added a button to change the selected data. when I use English language for editing the data, it works perfectly. But when I change the language, question mark is shown.
to edit the data I use the following commands.
sqlStr = "Update Employee Set FirstName = '" + FirstName.Text + "' Where ID = '" + ID.Text + "'";
cmd.CommandText = sqlStr;
cmd.Connection = connect;
cmd.ExecuteNonQuery();
any help is appreciated.
thanks

Change:
sqlStr = "Update Employee Set FirstName = '" + FirstName.Text + "' Where ID = '" + ID.Text + "'";
to:
sqlStr = "Update Employee Set FirstName = N'" + FirstName.Text + "' Where ID = N'" + ID.Text + "'";
Without the N at the start, you are using varchar rather than nvarchar. Which basically means that Persian characters will show as ?

I think you should use SqlParameters like this:
sqlStr = "Update Employee Set FirstName = #FirstName Where ID = #Id";
SqlParameter param = new SqlParameter();
param.ParameterName = "#FirstName";
param.Value = FirstName.Text;
cmd.Parameters.Add(param);
param = new SqlParameter();
param.ParameterName = "#Id";
param.Value = ID.Text;
cmd.Parameters.Add(param);
This, also, avoid sql injection.

c# Insert data into MySQL database using parameters

This probably a simple solution, but I've got a deadline to catch and I don't know the exact problem here.
So here's the deal, I'm trying to update my table using this piece of code:
private void btn_opslaan_Click(object sender, EventArgs e)
{
string opleidingsid = "Select OpleidingsID From opleidingen Where Opleidingsnaam = '" + cb_opleiding.Text + "'";
MySqlCommand cmdid = new MySqlCommand(opleidingsid, dbconnect.connection);
dbconnect.OpenConnection();
MySqlDataReader reader = cmdid.ExecuteReader();
reader.Read();
int oplid = (int)reader.GetValue(0);
cmdid.Dispose();
reader.Close();
sql = "UPDATE leerlingen SET Naam = '_naam', Adres = '_adres', Woonplaats = '_woonplaats', Postcode = '_postcode', Email = '_email', Telefoonnummer = '_telefoonnummer', Klas = '_klas', Ovnummer = '_ovnummer', OpleidingsID = '_opleidingsid', Startdatum = '_startdatum', Einddatum = '_einddatum' WHERE LeerlingID = '_leerlingid'";
// sql = "UPDATE leerlingen set Naam = '" + txt_naam.Text + "', Adres = '" + txt_adres.Text + "', Woonplaats = '" + txt_woonplaats.Text + "', Postcode = '" + txt_postcode.Text + "', Email = '" + txt_email.Text + "', Telefoonnummer = '" + txt_telefoonnumer.Text + "', Klas = '" + txt_klas.Text + "', Ovnummer = '" + txt_ovnummer.Text + "', OpleidingsID = '" + oplID + "', Startdatum = '"+mc_startdatum.SelectionStart.Date.ToString()+"', Einddatum = '"+ mc_einddatum.SelectionStart.Date.ToString() +"' WHERE LeerlingID = '" + Int32.Parse(lbl_leerlingid.Text) + "'";
MySqlCommand cmd = new MySqlCommand(sql, dbconnect.connection);
cmd.Parameters.AddWithValue("_naam", txt_naam.Text);
cmd.Parameters.AddWithValue("_adres", txt_adres.Text);
cmd.Parameters.AddWithValue("_woonplaats", txt_woonplaats.Text);
cmd.Parameters.AddWithValue("_postcode", txt_postcode.Text);
cmd.Parameters.AddWithValue("_email", txt_email.Text);
cmd.Parameters.AddWithValue("_telefoonnummer", txt_telefoonnumer.Text);
cmd.Parameters.AddWithValue("_klas", txt_klas.Text);
cmd.Parameters.AddWithValue("_ovnummer", txt_ovnummer.Text);
cmd.Parameters.AddWithValue("_opleidingsid", oplid);
cmd.Parameters.AddWithValue("_startdatum", mc_startdatum.SelectionStart.Date.ToString());
cmd.Parameters.AddWithValue("_einddatum", mc_einddatum.SelectionStart.Date.ToString());
cmd.Parameters.AddWithValue("_leerlingid", int.Parse(lbl_leerlingid.Text));
try
{
cmd.ExecuteNonQuery();
MessageBox.Show("opslaan gelukt");
}
catch (Exception error)
{
MessageBox.Show(error.ToString());
throw;
}
dbconnect.CloseConnection();
this.Close();
}
I've already tried without the single quotes, it would give me the error that colomn '_leerlingid' does not exist, but that is the parameter...
Now, I dont get any errors, but it wouldn't update my database.
Any help please
P.S. Ignore the sql injection please, before this , i didn't knew better before I found out about parameters.

Try replacing your parameters with the # symbol and remove the single quotes, like this:
SQL = "UPDATE leerlingen SET Naam = #naam, Adres = #adres";
cmd.Parameters.AddWithValue("#naam", txt_naam.Text);
cmd.Parameters.AddWithValue("#adres", txt_adres.Text);

I think what you did wrong is you mustn't initialize your MySqlCommand like that. It must be like this..
MySqlCommand cmd;
cmd = dbconnect.createCommand();
cmd.CommandText = "UPDATE tableName SET firstname=#firstname, lastname=#lastname where id=#id";
cmd.Parameters.AddWithValue("#id", idTxt.Text);
cmd.Parameters.AddWithValue("#firstname", fName.Text);
cmd.Parameters.AddWithValue("#lastname", lName.Text);
cmd.ExecuteNonQuery();

when I creating a new data in c#, I make it like this ..
//values
String a = "COL1ROW1", b = "COL1ROW2";
//this is the code for mysql
String query = "Insert Into tableName(Column1, Column2)values('" + a + "','" + b + "')";
//conn is your mysqlconnection
MySqlCommand cmd = new MySqlCommand(query, conn);
//then execute it
cmd.ExecuteNonQuery();

InvalidCastException, unhandled by user code [duplicate]

This question already has answers here:
ExecuteScalar(); With scope_identity() Generating "System.InvalidCastException: Specified cast is not valid" [duplicate]
(5 answers)
Closed 8 years ago.
My code is getting caught right here and I'm not sure why:
int newPersonID = (int)cmd.ExecuteScalar();
It says
Specified cast is not valid.
Can anyone help me out with this error? My PersonID is int type in the database table.
protected void AddNewCustomer(object sender, EventArgs e)
{
string nFirstName = ((TextBox)GridView1.FooterRow.FindControl("txtFirstName")).Text;
string nLastName = ((TextBox)GridView1.FooterRow.FindControl("txtLastName")).Text;
string nEmergency = ((TextBox)GridView1.FooterRow.FindControl("txtEmergency")).Text;
string nCell = ((TextBox)GridView1.FooterRow.FindControl("txtCell")).Text;
string nAge = ((TextBox)GridView1.FooterRow.FindControl("txtAge")).Text;
string nActivityCard = ((TextBox)GridView1.FooterRow.FindControl("txtActivityCard")).Text;
string nInitials = ((TextBox)GridView1.FooterRow.FindControl("txtInitials")).Text;
string nBoat = ((TextBox)GridView1.FooterRow.FindControl("txtBoat")).Text;
string nGroup = ((TextBox)GridView1.FooterRow.FindControl("txtGroup")).Text;
SqlConnection con = new SqlConnection(strConnString);
SqlCommand cmd = new SqlCommand("INSERT INTO Person(FirstName, LastName, Emergency#, Cell#, Age, ActivityCard, CraftType, Initials, Group#) " +
"values(#FirstName, #LastName, #Emergency, #Cell, #Age, #ActivityCard, #Boat, #Initials, #Group);" +
"SELECT SCOPE_IDENTITY();");
cmd.Parameters.Add("#FirstName", SqlDbType.VarChar).Value = nFirstName;
cmd.Parameters.Add("#LastName", SqlDbType.VarChar).Value = nLastName;
cmd.Parameters.Add("#Emergency", SqlDbType.NChar).Value = nEmergency;
cmd.Parameters.Add("#Cell", SqlDbType.NChar).Value = nCell;
cmd.Parameters.Add("#Age", SqlDbType.NChar).Value = nAge;
cmd.Parameters.Add("#ActivityCard", SqlDbType.NChar).Value = nActivityCard;
cmd.Parameters.Add("#Initials", SqlDbType.NChar).Value = nInitials;
cmd.Parameters.Add("#Boat", SqlDbType.VarChar).Value = nBoat;
cmd.Parameters.Add("#Group", SqlDbType.VarChar).Value = nGroup;
cmd.Connection = con;
con.Open();
int newPersonID = (int)cmd.ExecuteScalar();
con.Close();
SqlCommand cmd1 = new SqlCommand();
cmd1.CommandType = CommandType.Text;
cmd1.CommandText ="insert into TripSchedule(TripType, PersonID, Time, Date) values ('" + ddlTripType.SelectedItem + "', " + newPersonID + "', '" + ddlTripTime.SelectedItem + "', '" + TextBox1.Text + "');" +
"SELECT Person.PersonID, Person.FirstName AS FirstName, Person.LastName AS LastName, Person.Emergency# AS Emergency#, Person.Cell# AS Cell#, Person.Age AS Age, " +
"Person.ActivityCard AS ActivityCard, Person.CraftType AS CraftType, Person.Initials AS Initials, Person.Group# AS Group# " +
"FROM Person INNER JOIN " +
"TripSchedule ON Person.PersonID = TripSchedule.PersonID where TripSchedule.Date = '" + TextBox1.Text + "' and " +
"TripSchedule.Time = '" + ddlTripTime.SelectedItem + "' and TripSchedule.TripType = '" + ddlTripType.SelectedItem + "';";
GridView1.DataSource = GetData(cmd);
GridView1.DataBind();
}

Convert.ToInt32(cmd.ExecuteScalar());
Edited: That's right, view the answer in that question thread.

inserting or updating values into null textboxes

public void Updatecottonpurchase(int slipno, int basicprice, int premium, int totalamountpaid, int weight, int totalamountbasic, int totalamountpremium, int yeildestimates, int farmercode)
{
SqlConnection sqlConn = new SqlConnection(#"Data Source=TANYA-PC;Initial Catalog=biore1;Integrated Security=True");
try
{
string sqlQuery = "UPDATE cottonpurchse SET slipno = '" + slipno + "' , basic price = '" + basicprice + "' , premium = '" + premium + "' , totalamountpaid = '" + totalamountpaid + "' , weight = '" + weight + "' , totalamountbasic = '" + totalamountbasic + "' , totalamountpremium = '" + totalamountpremium + "' , yeildestimated = '" + yeildestimates + "' WHERE farmercode = '" + farmercode + "'";
SqlCommand cmd = new SqlCommand(sqlQuery, sqlConn);
sqlConn.Open();
cmd.ExecuteNonQuery();
sqlConn.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
sqlConn.Close();
}
finally
{
sqlConn.Close();
}
}
this is what ive done now yet nothing happens! i want to beable to update the null values but nothing happens! please help

This SQL code:
UPDATE TABLE cottonpurchase SET slipno= WHERE farmercode=
Does nothing, you need to add parameters,
see: http://www.csharp-station.com/Tutorials/AdoDotNet/Lesson06.aspx
You need to change the code into:
....
string queryString =
"UPDATE TABLE cottonpurchase SET slipno=#slipno WHERE farmercode=#farmercode";
try
{
connection.Open();
SqlCommand command = new SqlCommand(queryString, connection);
//define parameters used in command object
SqlParameter param = new SqlParameter();
param.ParameterName = "#slipno";
param.Value = inputfromsomewhere;
SqlParameter param = new SqlParameter();
param.ParameterName = "#farmercode";
param.Value = inputfromsomewhereelse;
//add new parameter to command object
command.Parameters.Add(param);
int result = command.ExecuteNonQuery();
//if result = 1 the update is performed
}
......

You need to add or choose a column for use as the primary key. The primary key should uniquely identify a row, and is used to locate the row to update.