This question already has answers here:
ExecuteNonQuery: Connection property has not been initialized.
(7 answers)
Closed 7 years ago.
I keep getting this error saying that "ExecuteScalar has not been initialized" I have new to C# but had a look through google and tutorials and still cant see what the problem is. Its probably a very silly mistake but if anyone could help. Thanks :)
// open connection
myConnection.Open();
// sql command
string Account_Num = txt_acc.Text;
string Pin_num = txt_pin.Text;
SqlCommand check_details = new SqlCommand("select Account_num, Pin_num from Cust_details where Account_num='" + txt_acc.Text + "'and Pin_num ='" + txt_pin.Text + "'");
check_details.Parameters.AddWithValue("#Account_num", txt_acc.Text);
check_details.Parameters.AddWithValue("#Pin_num", txt_pin.Text);
int result = Convert.ToInt32(check_details.ExecuteScalar());
if (result > 0)
{
Console.WriteLine("user exists");
}
else
{
Console.WriteLine("error");
}
}
Looks like you didn't connect your command with connection. Just set it's Connection property to myConnection.
check_details.Connection = myConnection;
or you can set it on your SqlCommand constructor as a second parameter;
SqlCommand check_details = new SqlCommand("yourCommand", myConnection);
or you can use CreateCommand method from your connection;
SqlCommand check_details = myConnection.CreateCommand();
And you are misunderstood the parameterized queries. You still do string concatenation in your sql query but you try to add parameters. That's meaningless.
Use using statement to dispose your connection and command automatically as well.
Also don't use AddWithValue as much as you can. It may generate unexpected and surprising results sometimes. Use Add method overload to specify your parameter type and it's size.
using(var myConnection = new SqlConnection(conString))
using(var check_details = myConnection.CreateCommand())
{
check_details.CommandText = #"select Account_num, Pin_num from Cust_details
where Account_num = #accnum
and Pin_num = #pinnum";
// I assume your column types as Int
check_details.Parameters.Add("#accnum", SqlDbType.Int).Value = int.Parse(txt_acc.Tex);
check_details.Parameters.Add("#pinnum", SqlDbType.Int).Value = int.Parse(txt_pin.Text);
myConnection.Open();
int result = (int)check_details.ExecuteScalar();
...
}
By the way, there is no point to select Pin_num column in your command since ExecuteScalar ignores it.
Related
I was creating an Appointment Table and i want to check if the row contains same Date,Slot,HR exists before another user enter.
The Connection is Opened Before this shown code.
SqlCommand slot_check = new SqlCommand("select * from Appointment where AppoinmentDate='"+textBox1.Text+"' and Slot='"+comboBox3.Text+ "'and HRName='" +comboBox2.Text+"'");
SqlDataReader Exist = slot_check.ExecuteReader();
if (Exist.HasRows)
{
string message = "Appointment Already Exists!!!!!";
MessageBox.Show(message);
}
else
{
string message = "Update";
MessageBox.Show(message);
}
System.InvalidOperationException: 'ExecuteReader: Connection property has not been initialized.'
To execute a command two informations are essential:
The sql string to execute and the connection to reach the database.
Without the connection your command cannot be executed because the framework doesn't know how to read or write the database.
There is an overload for the SqlCommand constructor that takes the two required parameters:
SqlCommand cmd = new SqlCommand(sqlText, connectionInstance);
So your code should be something like this
// The command text to run, without string concatenations and with parameters placeholders
string sqlText = #"select * from Appointment
where AppoinmentDate=#aptDate
and Slot=#slot
and HRName=#name";
// Using statement to correctly close and dispose the disposable objects
using(SqlConnection cnn = new SqlConnection(connectionString))
using(SqlCommand slot_check = new SqlCommand(sqlText, cnn))
{
// A parameter for each placeholder with the proper datatype
cmd.Parameters.Add("#aptDate", SqlDbType.Date).Value = Convert.ToDateTime(textBox1.Text);
cmd.Parameters.Add("#slot", SqlDbType.NVarChar).Value = comboBox3.Text;
cmd.Parameters.Add("#name", SqlDbType.NVarChar).Value = comboBox2.Text;
cnn.Open();
// Even the SqlDataReader is a disposable object
using(SqlDataReader Exist = slot_check.ExecuteReader())
{
if (Exist.HasRows)
{
string message = "Appointment Already Exists!!!!!";
MessageBox.Show(message + " " + Exist + comboBox2.Text);
}
else
{
string message = "Update";
MessageBox.Show(message);
}
}
}
As you can see the code now has a connection passed to the command constructor and a command text built without concatenating strings but using parameters.
Using parameters is a mandatory approach for any kind of database related operation. Without parameters your code could be exploited with the well known Sql Injection hack, but also, the simple presence of a single quote in your values, could break the sql syntax resulting in a Syntax Error Exception
Note that this code could still be wrong because I don't know what kind of data is stored in your table in the columns used in the WHERE statement. I assumed some kind of type but you should check against your table and verify if they are correct.
This question already has answers here:
How can I add user-supplied input to an SQL statement?
(2 answers)
Closed 4 years ago.
I'm facing a problem with decrementing value with MS Access database.
I get an error
Syntax error in UPDATE Statement
My code:
connection.Open();
command = new OleDbCommand();
command.Connection = connection;
command.CommandText = " update Cards set Count = Count - 1 where Type=" + ct + " ";
command.ExecuteNonQuery();
connection.Close();
Can anyone please help?
You should provide an actual error.
My guess is that count is a keyword and has to be put in square brackets like so [count]
and do use parameters, see Joel's answer
It's not certain, but I strongly suspect it's missing single quotes around ct. Fix it like this:
using (var connection = new OleDbConnection("connection string here"))
using (var command = new OleDbCommand("update Cards set Count = Count - 1 where Type= ?", connection))
{
//have to guess at the OleDbType value. Use the actual column type and length from the database
cmd.Parameters.Add("?", OleDbType.VarWChar, 10).Value = ct;
connection.Open();
command.ExecuteNonQuery();
}
There are several other important fixes in this pattern, too.
I have a local MS SQL Database, and I want to update one of it's bit field.
I have the following code:
static void UpgradeVevo(string nev)
{
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
SqlCommand command = new SqlCommand("UPDATE Vevok SET Torzsvendeg=True Where Nev=" + nev, connection);
command.ExecuteNonQuery();
}
Console.WriteLine(nev+" mostmár törzsvendég");
}
Torzsvendeg is a bit datatype(I have tried to set its value to 1 too), and Nev is varchar.
The connectionstring should be fine, since I have tried Select in another method and it works fine. The above code throws no exceptions, but the table does not get updated.
I have tried to find an answer for quite some time, with no success :/. Thank you for your help in advance!
True should be in a single quote since it's a string literal like
UPDATE Vevok SET Torzsvendeg='True'
Well brother, you are messed up with quotes. Your query should look like
"UPDATE Vevok SET Torzsvendeg = 1 Where Nev = '" + nev + "'"
Again, use parametarized query and not this concatenated one to avoid SQL Injection
If the column is a boolean (bit in sql server) then you will have to write
Torzsvendeg=1
instead of
Torzsvendeg='True'
or
Torzsvendeg=True
Edit:
Please try this:
static void UpgradeVevo(string nev)
{
var connection = new SqlConnection(connectionString))
connection.Open(); // try doing this without a using
SqlCommand command = new SqlCommand("UPDATE Vevok SET Torzsvendeg=#enabled Where Nev=#nev", connection);
command.Parameters.AddWithValue(#"enabled", 1);
command.Parameters.AddWithValue(#"nev", "vevo123");
command.ExecuteNonQuery();
command.Parameters.Clear(); // always clear after executed
// close connection when you shut down your application
connection.Close();
connection.Dispose();
Console.WriteLine(nev+" mostmár törzsvendég");
}
I am somwhat new to SQL, so I am not sure I am going about this the right way.
I am trying to fetch data from my SQL Server database where I want to find out if checkedin is 1/0, but it needs to search on a specific user and sort after the newest date as well.
What I am trying to do is something like this:
string connectionString = ".....";
SqlConnection cnn = new SqlConnection(connectionString);
SqlCommand checkForInOrOut = new SqlCommand("SELECT CHECKEDIN from timereg ORDER BY TIME DESC LIMIT 1 WHERE UNILOGIN = '" + publiclasses.unilogin + "'", cnn);
So my question, am I doing this right? And how do I fetch the data collected, if everything was handled correctly it should return 1 or 0. Should I use some sort of SqlDataReader? I am doing this in C#/WPF
Thanks
using (SqlDataReader myReader = checkForInOrOut.ExecuteReader())
{
while (myReader.Read())
{
string value = myReader["COLUMN NAME"].ToString();
}
}
This is how you would read data from SQL, but i recommend you looking into Parameters.AddWithValue
There are some errors in your query. First WHERE goes before ORDER BY and LIMIT is an MySql keyword while you are using the Sql Server classes. So you should use TOP value instead.
int checkedIn = 0;
string cmdText = #"SELECT TOP 1 CHECKEDIN from timereg
WHERE UNILOGIN = #unilogin
ORDER BY TIME DESC";
string connectionString = ".....";
using(SqlConnection cnn = new SqlConnection(connectionString))
using(SqlCommand checkForInOrOut = new SqlCommand(cmdText, cnn))
{
cnn.Open();
checkForInOrOut.Parameters.Add("#unilogin", SqlDbType.NVarChar).Value = publiclasses.unilogin;
// You return just one row and one column,
// so the best method to use is ExecuteScalar
object result = checkForInOrOut.ExecuteScalar();
// ExecuteScalar returns null if there is no match for your where condition
if(result != null)
{
MessageBox.Show("Login OK");
// Now convert the result variable to the exact datatype
// expected for checkedin, here I suppose you want an integer
checkedIN = Convert.ToInt32(result);
.....
}
else
MessageBox.Show("Login Failed");
}
Note how I have replaced your string concatenation with a proper use of parameters to avoid parsing problems and sql injection hacks. Finally every disposable object (connection in particular) should go inside a using block
Hi there its the first time to use stackoverflow so hi every one L)
i'm a beginner into C# forms i take it as a fun hobby.
SqlCommand comm = new SqlCommand("SELECT COUNT(*) FROM Members where sponser = "
+textbox1.text+"'", connection);
Int32 count = (Int32)comm.ExecuteScalar();
textbox2.Text ="Found "+ count+" Members;
well its just a mix between 2 codes i have got from google xD
how ever the error appear here textbox2.Text ="Found "+ count+" Members;
There are a couple of things wrong with this line of code:
textbox2.Text ="Found "+ count+" Members;
First of all, there's a syntax error. You never close the second set of quotes. You'd do so like this:
textbox2.Text ="Found "+ count+" Members";
However, string concatenation like this is still a little messy. You have two literal strings and you're trying to add them to an integer, which isn't entirely intuitive (and probably slower than it needs to be). Instead, consider using a formatting string:
textbox2.Text = string.Format("Found {0} Members", count);
This will take the value from count (which is an integer) and, internally to the string.Format() function, discern its string representation and insert it into the placeholder in the formatted string.
UPDATE: That takes care of the compile-time errors. Now you're going to get a run-time error from this:
SqlCommand comm = new SqlCommand("SELECT COUNT(*) FROM Members where sponser = "
+textbox1.text+"'", connection);
As soon as you try to execute that SQL statement you're going to get an error from the database because the resulting query has a syntax error:
SELECT COUNT(*) FROM Members where sponser = some text'
You're missing the opening single-quote for the parameter. Something like this:
SqlCommand comm = new SqlCommand("SELECT COUNT(*) FROM Members where sponser = '"
+textbox1.text+"'", connection);
However, and this is important, you're still not done. This line of code is wide open to a very common and easily exploitable vulnerability called SQL Injection. You'll want to move away from direct string concatenation and use parameters for your SQL queries. Something like this:
SqlCommand cmd = new SqlCommand("SELECT COUNT(*) FROM Members where sponser = #sponser");
cmd.Parameters.Add("#sponser", textbox1.text);
Int32 count = (Int32)comm.ExecuteScalar();
Know that there is still a lot more you can do to improve this, which is all worth learning over time. Things you can look into are:
Checking and validating user input (textbox1.text) before you even try to use it in a SQL query.
Checking the output of comm.ExecuteScalar() before trying to directly cast it to an Int32 (this would give you a runtime error if it returns anything other than an integer for some reason).
Consider using something like Linq to Sql in place of ADO.NET components as it does a lot more for you with less code on your part.
protected void Page_Load(object sender, EventArgs e)
{
lb1.Text = GetRecordCount(textbox2.Text).ToString();
}
private int GetRecordCount(string myParameter)
{
string connectionString = ConfigurationManager.ConnectionStrings["DBConnection"].ToString();
Int32 count = 0;
string sql = "SELECT COUNT(*) FROM members WHERE sponsor = #Sponsor";
using (SqlConnection conn = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.Add("#Sponsor", SqlDbType.VarChar);
cmd.Parameters["#Sponsor"].Value = myParameter;
try
{
conn.Open();
count = (Int32)cmd.ExecuteScalar();
}
catch (Exception ex)
{
}
}
return (int)count;
}
You are missing a closing " at the end:
textbox2.Text ="Found "+ count+" Members";
You code is vulnerable to SQL Injections. Please consider using Parameters.
private int GetMemberCount(string connectionString, string sponsor)
{
using(var connection = new SqlConnection(connectionString))
using(var command = connection.CreateCommand())
{
command.CommandText = "SELECT COUNT(*) FROM members WHERE sponsor = #Sponsor";
command.Parameters.AddWithValue("#Sponsor", sponsor);
return Convert.ToInt32(command.ExecuteScalar());
}
}
//Usage
var sponsor = textbox1.text;
var count = GetMemberCount(connectionString, sponsor);
textbox2.Text = string.Format("Found {0} Members", count);