We Keep Coding

"ExecuteScalar: Connection property has not been initialized."

I'm new to c# and currently I have some problems when I'm running this program without debugging.
This is the login page for my project. I've create a service-based database and I want to connect to the data which is username and password in the table 'Table' which is in the database.
However, I've encountered an issue which is "ExecuteScalar: Connection property has not been initialized." when I'm running this code.
Can anyone help me with this?
private void button1_Click(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=c:\users\hp\documents\visual studio 2015\Projects\PersonalFinancialSoftware\PersonalFinancialSoftware\Login.mdf;Integrated Security=True");
SqlCommand cmd = new SqlCommand();
cmd.CommandText = "SELECT COUNT (*) FROM Table where UserID = #userid AND Password = #password";
cmd.Parameters.AddWithValue("#userid", textBox1.Text);
cmd.Parameters.AddWithValue("#password", textBox2.Text);
object result = cmd.ExecuteScalar();
conn.Open();
string useridlogin = Convert.ToString(result);
conn.Close();
if (useridlogin != " ")
{
Home_Page homepage = new Home_Page();
homepage.Show();
}
else
{
MessageBox.Show("Invalid ID or password, please try again!", "Info", MessageBoxButtons.OK);
}
}

I can see that you've executed the ExecuteScalar method before opening the SQL Database connection, resulting in error you're getting.
Open the connection before ExecuteScalar method, and you're done.
private void button1_Click(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=c:\users\hp\documents\visual studio 2015\Projects\PersonalFinancialSoftware\PersonalFinancialSoftware\Login.mdf;Integrated Security=True");
conn.Open();
SqlCommand cmd = new SqlCommand();
cmd.CommandText = "SELECT COUNT (*) FROM Table where UserID = #userid AND Password = #password";
cmd.Parameters.AddWithValue("#userid", textBox1.Text);
cmd.Parameters.AddWithValue("#password", textBox2.Text);
object result = cmd.ExecuteScalar();
string useridlogin = Convert.ToString(result);
conn.Close();
if (useridlogin != " ")
{
Home_Page homepage = new Home_Page();
homepage.Show();
}
else
{
MessageBox.Show("Invalid ID or password, please try again!", "Info", MessageBoxButtons.OK);
}
}

You have open connection after ExecuteScalar thats you are getting error, You must open connection befor ExecuteScalar try this code
private void button1_Click(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=c:\users\hp\documents\visual studio 2015\Projects\PersonalFinancialSoftware\PersonalFinancialSoftware\Login.mdf;Integrated Security=True");
SqlCommand cmd = new SqlCommand();
conn.Open();
cmd.CommandText = "SELECT COUNT (*) FROM Table where UserID = #userid AND Password = #password";
cmd.Parameters.AddWithValue("#userid", textBox1.Text);
cmd.Parameters.AddWithValue("#password", textBox2.Text);
object result = cmd.ExecuteScalar();
string useridlogin = Convert.ToString(result);
conn.Close();
if (useridlogin != " ")
{
Home_Page homepage = new Home_Page();
homepage.Show();
}
else
{
MessageBox.Show("Invalid ID or password, please try again!", "Info", MessageBoxButtons.OK);
}
}
In your code SQL query find connection. But you have open it after ExecuteScalar so this is giving you an error.

why my password isn't changed?

I want to change password that saved in db,but my code dose not work. what is wrong? I always see the last message:
unable to connect database
public partial class pws : System.Web.UI.Page
{
static string strcon = (System.Web.Configuration.WebConfigurationManager.ConnectionStrings["strcon"].ConnectionString);
protected void Page_Load(object sender, EventArgs e)
{
}
private void ShowPopUpMsg(string msg)
{
StringBuilder sb = new StringBuilder();
sb.Append("alert('");
sb.Append(msg.Replace("\n", "\\n").Replace("\r", "").Replace("'", "\\'"));
sb.Append("');");
ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "showalert", sb.ToString(), true);
}
protected void btnInsert_Click(object sender, EventArgs e)
{
try {
SqlConnection db = new SqlConnection(strcon);
db.Open();
string strId = string.Empty;
string strusername = string.Empty;
string OLdpassword = string.Empty;
SqlCommand cmd;
cmd = new SqlCommand("SELECT * FROM login WHERE login_username =#login_username ", db);
cmd.Parameters.AddWithValue("login_username", txtOldUsername.Text);
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
cmd.Dispose();
cmd = null;
db.Close();
db.Open();
SqlDataReader DR;
DR = cmd.ExecuteReader();
if (DR.Read())
{
strId = DR["login_id"].ToString();
strusername = DR["login_username"].ToString();
OLdpassword = DR["login_Password"].ToString();
}
db.Close();
if (OLdpassword == txtOldPass.Text)
{
db.Open();
string Command = "Update login Set login_Password= #login_Password WHERE login_username=#login_username";
SqlCommand cmdIns = new SqlCommand(Command, db);
cmdIns.Parameters.AddWithValue("#login_Password ", txtNewPass.Text);
cmdIns.Parameters.AddWithValue("#login_username ", txtOldUsername.Text);
cmdIns.ExecuteNonQuery();
cmdIns.Parameters.Clear();
cmdIns.Dispose();
cmdIns = null;
db.Close();
ShowPopUpMsg("successful");
}
else
{
ShowPopUpMsg(" old pass is not correct");
}
}
catch
{
ShowPopUpMsg("unable to connect database");
}
}
}

this part:
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
cmd.Dispose();
cmd = null;
db.Close();
db.Open();
SqlDataReader DR;
DR = cmd.ExecuteReader();
why do you execute a non query, which is a query (select * from ...)?
why do you dispose the SqlCommand object cmd and why do you reuse it after disposing?
why do you close and open the line below?
I would rewrite those lines it like this:
SqlDataReader DR = cmd.ExecuteReader();
I would recomment a using statement or closing the connection in a finally block:
SqlConnection db = new SqlConnection(strcon);
try{
db.Open();
//.... the rest
}
catch(Exception ex)
{
ShowPopUpMsg("unable to connect database: " + ex.Message);
}
finally
{
db.Close();
}
and another thing: I would use the primary key in the update statement. where id = login_id instead of the username. unless the username is set to "unique"

Check if you can connect to the database using your credentials and database management tool (I assume you you use MS SQL Server so use MS SQL Server Management Studio)
Check if the format of your connection string is correct. You can use this website http://www.connectionstrings.com/ to do it.
I hope this will help you.

Try to step through the code and find where the exception occures, and look at the details of the exception.
My guess is that there are something wrong with you connection string (strcon).

SQL Insert Query Using C#

I'm having an issue at the moment which I am trying to fix. I just tried to access a database and insert some values with the help of C#
The things I tried (worked)
String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES ('abc', 'abc', 'abc', 'abc')";
A new line was inserted and everything worked fine, now I tried to insert a row using variables:
String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES (#id, #username, #password, #email)";
command.Parameters.AddWithValue("#id","abc")
command.Parameters.AddWithValue("#username","abc")
command.Parameters.AddWithValue("#password","abc")
command.Parameters.AddWithValue("#email","abc")
command.ExecuteNonQuery();
Didn't work, no values were inserted. I tried one more thing
command.Parameters.AddWithValue("#id", SqlDbType.NChar);
command.Parameters["#id"].Value = "abc";
command.Parameters.AddWithValue("#username", SqlDbType.NChar);
command.Parameters["#username"].Value = "abc";
command.Parameters.AddWithValue("#password", SqlDbType.NChar);
command.Parameters["#password"].Value = "abc";
command.Parameters.AddWithValue("#email", SqlDbType.NChar);
command.Parameters["#email"].Value = "abc";
command.ExecuteNonQuery();
May anyone tell me what I am doing wrong?
Kind regards
EDIT:
in one other line I was creating a new SQL-Command
var cmd = new SqlCommand(query, connection);
Still not working and I can't find anything wrong in the code above.

I assume you have a connection to your database and you can not do the insert parameters using c #.
You are not adding the parameters in your query. It should look like:
String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES (#id,#username,#password, #email)";
SqlCommand command = new SqlCommand(query, db.Connection);
command.Parameters.Add("#id","abc");
command.Parameters.Add("#username","abc");
command.Parameters.Add("#password","abc");
command.Parameters.Add("#email","abc");
command.ExecuteNonQuery();
Updated:
using(SqlConnection connection = new SqlConnection(_connectionString))
{
String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES (#id,#username,#password, #email)";
using(SqlCommand command = new SqlCommand(query, connection))
{
command.Parameters.AddWithValue("#id", "abc");
command.Parameters.AddWithValue("#username", "abc");
command.Parameters.AddWithValue("#password", "abc");
command.Parameters.AddWithValue("#email", "abc");
connection.Open();
int result = command.ExecuteNonQuery();
// Check Error
if(result < 0)
Console.WriteLine("Error inserting data into Database!");
}
}

Try
String query = "INSERT INTO dbo.SMS_PW (id,username,password,email) VALUES (#id,#username, #password, #email)";
using(SqlConnection connection = new SqlConnection(connectionString))
using(SqlCommand command = new SqlCommand(query, connection))
{
//a shorter syntax to adding parameters
command.Parameters.Add("#id", SqlDbType.NChar).Value = "abc";
command.Parameters.Add("#username", SqlDbType.NChar).Value = "abc";
//a longer syntax for adding parameters
command.Parameters.Add("#password", SqlDbType.NChar).Value = "abc";
command.Parameters.Add("#email", SqlDbType.NChar).Value = "abc";
//make sure you open and close(after executing) the connection
connection.Open();
command.ExecuteNonQuery();
}

The most common mistake (especially when using express) to the "my insert didn't happen" is : looking in the wrong file.
If you are using file-based express (rather than strongly attached), then the file in your project folder (say, c:\dev\myproject\mydb.mbd) is not the file that is used in your program. When you build, that file is copied - for example to c:\dev\myproject\bin\debug\mydb.mbd; your program executes in the context of c:\dev\myproject\bin\debug\, and so it is here that you need to look to see if the edit actually happened. To check for sure: query for the data inside the application (after inserting it).

static SqlConnection myConnection;
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
myConnection = new SqlConnection("server=localhost;" +
"Trusted_Connection=true;" +
"database=zxc; " +
"connection timeout=30");
try
{
myConnection.Open();
label1.Text = "connect successful";
}
catch (SqlException ex)
{
label1.Text = "connect fail";
MessageBox.Show(ex.Message);
}
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button2_Click(object sender, EventArgs e)
{
String st = "INSERT INTO supplier(supplier_id, supplier_name)VALUES(" + textBox1.Text + ", " + textBox2.Text + ")";
SqlCommand sqlcom = new SqlCommand(st, myConnection);
try
{
sqlcom.ExecuteNonQuery();
MessageBox.Show("insert successful");
}
catch (SqlException ex)
{
MessageBox.Show(ex.Message);
}
}

private void button1_Click(object sender, EventArgs e)
{
String query = "INSERT INTO product (productid, productname,productdesc,productqty) VALUES (#txtitemid,#txtitemname,#txtitemdesc,#txtitemqty)";
try
{
using (SqlCommand command = new SqlCommand(query, con))
{
command.Parameters.AddWithValue("#txtitemid", txtitemid.Text);
command.Parameters.AddWithValue("#txtitemname", txtitemname.Text);
command.Parameters.AddWithValue("#txtitemdesc", txtitemdesc.Text);
command.Parameters.AddWithValue("#txtitemqty", txtitemqty.Text);
con.Open();
int result = command.ExecuteNonQuery();
// Check Error
if (result < 0)
MessageBox.Show("Error");
MessageBox.Show("Record...!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
con.Close();
loader();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
con.Close();
}
}

public static string textDataSource = "Data Source=localhost;Initial
Catalog=TEST_C;User ID=sa;Password=P#ssw0rd";
public static bool ExtSql(string sql) {
SqlConnection cnn;
SqlCommand cmd;
cnn = new SqlConnection(textDataSource);
cmd = new SqlCommand(sql, cnn);
try {
cnn.Open();
cmd.ExecuteNonQuery();
cnn.Close();
return true;
}
catch (Exception) {
return false;
}
finally {
cmd.Dispose();
cnn = null;
cmd = null;
}
}

I have just wrote a reusable method for that, there is no answer here with reusable method so why not to share...here is the code from my current project:
public static int ParametersCommand(string query,List<SqlParameter> parameters)
{
SqlConnection connection = new SqlConnection(ConnectionString);
try
{
using (SqlCommand cmd = new SqlCommand(query, connection))
{ // for cases where no parameters needed
if (parameters != null)
{
cmd.Parameters.AddRange(parameters.ToArray());
}
connection.Open();
int result = cmd.ExecuteNonQuery();
return result;
}
}
catch (Exception ex)
{
AddEventToEventLogTable("ERROR in DAL.DataBase.ParametersCommand() method: " + ex.Message, 1);
return 0;
throw;
}
finally
{
CloseConnection(ref connection);
}
}
private static void CloseConnection(ref SqlConnection conn)
{
if (conn.State != ConnectionState.Closed)
{
conn.Close();
conn.Dispose();
}
}

class Program
{
static void Main(string[] args)
{
string connetionString = null;
SqlConnection connection;
SqlCommand command;
string sql = null;
connetionString = "Data Source=Server Name;Initial Catalog=DataBaseName;User ID=UserID;Password=Password";
sql = "INSERT INTO LoanRequest(idLoanRequest,RequestDate,Pickupdate,ReturnDate,EventDescription,LocationOfEvent,ApprovalComments,Quantity,Approved,EquipmentAvailable,ModifyRequest,Equipment,Requester)VALUES('5','2016-1-1','2016-2-2','2016-3-3','DescP','Loca1','Appcoment','2','true','true','true','4','5')";
connection = new SqlConnection(connetionString);
try
{
connection.Open();
Console.WriteLine(" Connection Opened ");
command = new SqlCommand(sql, connection);
SqlDataReader dr1 = command.ExecuteReader();
connection.Close();
}
catch (Exception ex)
{
Console.WriteLine("Can not open connection ! ");
}
}
}

C# Database issue

Could somebody tell me why this isn't adding the values to the database. The form runs fine and doesn't return any errors.
private void button1_Click(object sender, EventArgs e)
{
SqlConnection connection = new SqlConnection();
SqlCommand command = new SqlCommand();
connection.ConnectionString = (#"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\John\Documents\Setup.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
command.Parameters.AddWithValue("#userName", textBox1.Text);
command.Parameters.AddWithValue("#passWord", textBox2.Text);
command.CommandText = "INSERT INTO Setup (userName, password) VALUES(#userName, #passWord)";
try
{
connection.Open();
int rowsAffected = command.ExecuteNonQuery();
}
catch (Exception ex)
{
// handle exception
}
finally
{
connection.Close();
}
}
FYI: I'm a "newbie" My database is called Setup. I've manually added a table called myTable with 2 columns of userName and another one called password both set at nchar(50)

You need to specify the Table, not the database (which gets used in the connection string). Added the schema prefix to the table name:
command.CommandText = "INSERT INTO dbo.myTable (userName, password) VALUES (#userName, #passWord)";
And add:
command.Connection = connection;
to associate your Command object with the connection object.

Your code should look something like this:
Set the connection object.
Specify the table name as #LarsTech has mentioned.
It is a best practice to use two part notation when specifying table names like [Schema name].[Table Name]. So, you have to specify your table name like dbo.MyTable
Code snippet:
private void button1_Click(object sender, EventArgs e)
{
SqlConnection connection = new SqlConnection();
connection.ConnectionString = (#"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\John\Documents\Setup.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True;");
SqlCommand command = new SqlCommand();
command.Connection = connection;
command.CommandText = "INSERT INTO dbo.MyTable (userName, password) VALUES (#userName, #passWord)";
command.Parameters.AddWithValue("#userName", textBox1.Text);
command.Parameters.AddWithValue("#passWord", textBox2.Text);
try
{
connection.Open();
int rowsAffected = command.ExecuteNonQuery();
}
catch (Exception ex)
{
//handle exception
}
finally
{
connection.Close();
}
}

The form runs fine and doesn't return any errors.
That's probably because you're swallowing them. Get rid of (or log) your catch (Exception ex).
In general, the .NET BCL is well-designed - if a method isn't going to work, you will get an exception.
[Now] I have the error 'ExecuteNonQuery: Connection property has not been initialized.'
Right. You need to pass the SqlConnection to the SqlCommand:
SqlCommand command = new SqlCommand();
command.Connection = connection;

check existing record before inserting sql database

I created a simple asp.net form which allow users to view a list of dates for a training and register for that date , they enter their name and employeeid manually ( i dont want to allow dulpicate employe ids), so I need to figure out how to check this on c#..
code:
public string GetConnectionString()
{
//sets the connection string from your web config file "ConnString" is the name of your Connection String
return System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
}
private void checkContraint()
{
SqlConnection conn = new SqlConnection(GetConnectionString());
string sql = "Select "; //NEED HELP HERE
}
private void InsertInfo()
{
var dateSelected = dpDate.SelectedItem.Value;
SqlConnection conn = new SqlConnection(GetConnectionString());
string sql = "INSERT INTO personTraining (name,department,title,employeeid,training_id, training,trainingDate,trainingHour, trainingSession)SELECT #Val1b+','+#Val1,#Val2,#Val3,#Val4,training_id,training,trainingDate,trainingHour,trainingSession FROM tbl_training WHERE training_id =#training_id ";
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.AddWithValue("#Val1", txtName.Text);
cmd.Parameters.AddWithValue("#Val1b", txtLname.Text);
cmd.Parameters.AddWithValue("#Val2", txtDept.Text);
cmd.Parameters.AddWithValue("#Val3", txtTitle.Text);
cmd.Parameters.AddWithValue("#Val4", txtEmployeeID.Text);
//Parameter to pass for the select statement
cmd.Parameters.AddWithValue("#training_id", dateSelected);
cmd.CommandType = CommandType.Text;
//cmd.ExecuteNonQuery();
int rowsAffected = cmd.ExecuteNonQuery();
if (rowsAffected == 1)
{
//Success notification // Sends user to redirect page
Response.Redirect(Button1.CommandArgument.ToString());
ClearForm();
}
else
{
//Error notification
}
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Insert Error:";
msg += ex.Message;
throw new Exception(msg);
}
finally
{
conn.Close();
}
}
protected void Button1_Click(object sender, EventArgs e)
{
checkContraint();
InsertInfo();

this way , your query will insert data only if not exists already
string sql = "INSERT INTO personTraining (name,department,title,employeeid,training_id, training,trainingDate,trainingHour, trainingSession)SELECT #Val1b+','+#Val1,#Val2,#Val3,#Val4,training_id,training,trainingDate,trainingHour,trainingSession FROM tbl_training WHERE training_id =#training_id and not exists (select 1 from personTraining pp where pp .employeeid=#Val4) ";