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Getting connection Open when Using a SqlConnection block within Another Block

In the project I call a method to query additional information with a SqlConnection block, but then I validate if exists in a second table using another sqlconnection block, but it is supposed to be disposed (closed) after getting back to the method InsertNewData, but when calling to Open the connection for the Insert, I'm getting the following message:
The connection was not closed. The connection's current state is open.
My code is like this:
public void InsertNewData(string operation)
{
DataTable dt = new DataTable();
try
{
if (operation!= string.Empty)
{
using (SqlConnection oconn = new SqlConnection(myDBone))
{
SqlCommand cmd = new SqlCommand();
SqlDataAdapter da = new SqlDataAdapter();
string query = "SELECT * FROM operations "+
"WHERE idoper=#id";
oconn.Open();
cmd = new SqlCommand(query, oconn);
cmd.Parameters.Add(new SqlParameter("#id", operation.ToString()));
da = new SqlDataAdapter(cmd);
da.Fill(dt);
}
if (dt.Rows.Count > 0)
{
using (SqlConnection con = new SqlConnection(myDBtwo))
{
SqlCommand com = new SqlCommand();
string query= "";
foreach (DataRow x in dt.Rows)
{
if (ValidateData(x) == false)
{
query= "INSERT INTO history(iddata,description, datehist ) "+
" VALUES(#id,#descrip,GETDATE())";
con.Open(); //Here throws the Exception error
com = new SqlCommand(query, con);
com.Parameters.Add(new SqlParameter("#id", x["idoper"].ToString()));
com.Parameters.Add(new SqlParameter("#descrip", x["description"] ));
com.ExecuteNonQuery();
}
}
}
}
}
}
catch (Exception x)
{
throw x;
}
}
public bool ValidateData(DataRow row)
{
bool exists= false;
string operation= row["idoper"].ToString();
string descrip= row["description"].ToString();
if (operation!= string.Empty && descrip!= string.Empty)
{
using (SqlConnection oconn = new SqlConnection(sqlrastreo))
{
SqlCommand cmd = new SqlCommand();
string query = "SELECT COUNT(*) FROM history "+
"WHERE iddata=#id AND description=#descrip";
oconn.Open();
cmd = new SqlCommand(query, oconn);
com.Parameters.Add(new SqlParameter("#id", operation));
com.Parameters.Add(new SqlParameter("#descrip", descrip));
int count = (int) cmd.ExecuteScalar();
if (count > 0)
exists= true;
}// Here it should be Disposed or closed the SqlConnection
}
return exists;
}
What I'm doing wrong, because it's suppose to be closed the other connection and the other hasn't been opened ? or Should I Still call the Close() method for each SqlConnection inside the block Using?
Updated:
I've changed to parameters for best reading code and recommendation syntax.
NOTE
The values and parameters aren't the real ones, my real table descriptions have about 8 fields, but I validate with just two parameters that aren't primary key, but considering that I can't edit the table properties (Have only reading permissions for that database).
Update 2:
Thanks to the recommendation of Sean Lange, it was better and so simple to use a Store Procedure (SP) to validate and insert at the same time, so I do it as follow in code of the process:
public void InsertNewData(string operation)
{
try
{
if(operation == string.Empty)
return;
using(SqlConnection con = new SqlConnection(myDBtwo))
{
con.Open();
var cmd = new SqlCommand("SP_InsertData", con);
cmd.Parameters.Add(new SqlParameter("#id", operation));
cmd.ExecuteNonQuery();
}
}
catch(Exception ex)
{ throw ex; }
}
And then in my SP I insert a select statement of the parameter, to avoid duplicates and also do it in One go:
CREATE PROCEDURE SP_InsertData #id VARCHAR(10)
AS
BEGIN
INSERT INTO History
SELECT O.idoper, O.description
FROM myDBone.dbo.operations O
LEFT JOIN History H
ON H.iddata = O.idoper AND H.description = O.description
WHERE O.idoper=#id AND H.iddata IS NULL
END
Thanks for your support, and hope it helps someone.

First your code is badly written,as they have suggested you don't need to validate,try catch will do it for you.second opening a connection inside a loop ( foreach in your case) will will result to trying to open already open connection. Example here you could do something like
query= "INSERT INTO history(iddata,description, datehist" VALUES(#id,#descrip,GETDATE())";
using (SqlConnection con = new SqlConnection(myDBtwo))
{
con.Open();
SqlCommand com = new SqlCommand(query,con);
foreach (DataRow x in dt.Rows)
{
com.Parameters.Add(new SqlParameter("#id", x["idoper"].ToString()));
com.Parameters.Add(new SqlParameter("#descrip", x["description"] ));
com.ExecuteNonQuery();
}
}
}

C# SQL, Multiple Commands

I'm trying to write a method which should communicate with database, but I'm not sure if my approach is right.
public void dbWorkerLogin(int workerNumber) {
// Connection string stored in "conn"
if (!new SqlCommand("Some Command WHERE id=" +workernumber,conn).executeReader().HasRows)
{
new SqlCommand("exec STORED_PROCEDURE1 " + workerNumber, conn).ExecuteNonQuery();
new SqlCommand("exec STORED_PROCEDURE2 " + workerNumber, conn).ExecuteNonQuery();
}
else
{
new SqlCommand("exec STORED_PROCEDURE3 " + workerNumber,conn).ExecuteNonQuerry();
}
1) Is it ok to write it like this and start each SqlCommand with keyword new? Or should I do something like:
SqlCommand command = new SqlCommand(null, conn);
command = ...;
and then recycle the variable 'command' or this way?
using(SqlCommand cmd = new SqlCommand("COMMAND", conn);
2) Will my procedures work or should I use SqlCommand.Prepare() function that will covert my data into correct datatypes? eg. workerNumber is int, but in database it is stored as decimal.
using (SqlCommand cmd = new SqlCommand("STORED_PROCEDURE", conn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parametres.Add("#id", SqlDbType.Decimal).Value = workNumber;
cmd.Prepare();
cmd.ExecuteNonQuery();
}
Can you please somehow sum up what to use, what better not to? Unfortunately I can't test that first code because of limited access to DB so I'm not sure if it can be executed without errors or not.
Thank you for any help on this subject!
EDIT:
After a few hours I reach to this stage:
public int getWorkerNumber(string uniqueID)
{
using (conn = new SqlConnection(ConfigurationManager.ConnectionStrings["dbConnect"].ConnectionString))
{
conn.Open();
using (SqlCommand cmd = new SqlCommand("SELECT number FROM worker WHERE workerID = #id",conn))
{
cmd.Parameters.Add("#id", SqlDbType.Decimal).Value = uniqueID;
using (SqlDataReader reader = cmd.ExecuteReader())
{
int answer;
while (reader.Read())
{
answer = (int)reader.GetDecimal(0);
}
return answer;
}
}
}
}
And this one:
public string dbLoginWorker(int workerNumber)
{
SqlCommand cmd;
SqlDataReader reader;
using (conn = new SqlConnection(ConfigurationManager.ConnectionStrings["dbConnect"].ConnectionString))
{
conn.Open();
cmd = new SqlCommand("SELECT column FROM table WHERE id= #workernumber", conn);
cmd.Parameters.Add("#workernumber", SqlDbType.Decimal).Value = workerNumber;
reader = cmd.ExecuteReader();
if (!reader.HasRows)
{
cmd = new SqlCommand("STORED_PROCEDURE1", conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("#ID", SqlDbType.Decimal).Value = workerNumber;
cmd.Parameters.Add("#VARCHAR", SqlDbType.VarChar).Value = "text";
cmd.Prepare();
reader.Close();
cmd.ExecuteNonQuery();
cmd.Dispose();
reader.Dispose();
return "procedure 1 executed";
else
{
cmd = new SqlCommand("STORED_PROCEDURE2", conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("#ID", SqlDbType.Decimal).Value = workerNumber;
cmd.Parameters.Add("#INT", SqlDbType.SmallInt).Value = 1;
cmd.Parameters.Add("#VARCHAR", SqlDbType.VarChar).Value = "text";
cmd.Prepare();
reader.Close();
cmd.ExecuteNonQuery();
cmd.Dispose();
reader.Dispose();
return "procedure 2 executed";
}
}
}
Both methods are functional (if I did no mistake in rewriting :) ). I'm not sure which of these methods (1st or 2nd) are better in terms of stability and if this approach is better and more ressistant to SQL Injection. Can someone comment on this subject? Thank you again for any help!

1) It is best to always use USING blocks when possible. This includes SqlConnection, SqlCommand, SqlReader and other objects that implement IDisposable. USING blocks automatically close and dispose of the objects, so you do not have to do so.
2) I believe that you are using the Prepare() method in the wrong place. Look at the following StackOverflow article for proper usage:
PrepareMethodInstructions.
3) in the dbLoginWorker() method, the first query is just used to determine if rows are found. Therefore, I suggest changing the SELECT command to SELECT TOP 1 column FROM table WHERE id= #workernumber so that the query is faster and more efficient.
4) I do not believe your commands are subject to SQL Injection attacks because they are fully parameterized. Good job on that one.
5) As a general thought, I suggest reading up on refactoring techniques. Your dbLoginWorker() method could be made more readable and maintainable, as well as self-documenting, if you created three additional methods, one for each SQL command, and named them something appropriate. You could also setup a method for creating a connection based on a connection name, and you would not have as much duplicate code. For example:
public static SqlConnection GetConnection(string connectionName)
{
SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings[connectionName].ConnectionString);
conn.Open();
return conn;
}
public string dbLoginWorker(int workerNumber)
{
using (conn = GetConnection("dbConnect"))
{
if (CanFindWorkerNumber(conn, workerNumber))
ExecuteProcedure1(conn);
else
ExecuteProcedure2(conn);
}
}
public bool CanFindWorkerNumber (SqlConnection conn, int workerNumber)
{
bool success = false;
using (SqlCommand cmd = new SqlCommand("SELECT TOP 1 column FROM table WHERE id= #workernumber", conn))
{
cmd.Parameters.Add("#workernumber", SqlDbType.Decimal);
cmd.Prepare();
cmd.Parameters[0].Value = workerNumber;
success = cmd.ExecuteScalar() != null;
}
return success;
}
public void ExecuteProcedure1(SqlConnection conn)
{
using (SqlCommand cmd = new SqlCommand("STORED_PROCEDURE1", conn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("#ID", SqlDbType.Decimal);
cmd.Parameters.Add("#VARCHAR", SqlDbType.VarChar);
cmd.Prepare();
cmd.Parameters[0].Value = workerNumber;
cmd.Parameters[1].Value = "text";
cmd.ExecuteNonQuery();
}
}
public void ExecuteProcedure1(SqlConnection conn)
{
using (SqlCommand cmd = new SqlCommand("STORED_PROCEDURE1", conn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("#ID", SqlDbType.Decimal);
cmd.Parameters.Add("#INT", SqlDbType.SmallInt).Value);
cmd.Parameters.Add("#VARCHAR", SqlDbType.VarChar);
cmd.Prepare();
cmd.Parameters[0] = workerNumber;
cmd.Parameters[1] = 1;
cmd.Parameters[2] = "text";
cmd.ExecuteNonQuery();
}
}

You could actually do this in one SQL commend. Right now you are pulling back a result set only to see if it has rows or not, then executing different commands based on that. You should be able to do that in one command, disposing of it and the connection appropriately:
var sql =
#"
IF EXISTS(Some Command WHERE id=#workernumber)
BEGIN
exec STORED_PROCEDURE1 #workernumber;
exec STORED_PROCEDURE2 #workernumber;
END
ELSE
exec STORED_PROCEDURE3 #workernumber;
";
Note that you're not vulnerable to SQL injection because you're not dealing with strings, only integers.

Showing MessageBox when value is lower than -

Basically I want a MessageBox that appears when my Form is loaded that is saying that the value is lower than a constant value ( like 30 ).
This is the code I just wrote but its not working since the IF condition is not syntactly correct.
private void button2_Click(object sender, EventArgs e)
{
System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection();
conn.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=|DataDirectory|DataMG.mdb";
System.Data.OleDb.OleDbCommand cmd = new System.Data.OleDb.OleDbCommand();
cmd.CommandType = System.Data.CommandType.Text;
cmd.CommandText = "Select COUNT(*) from Prodotti where Disponibilta < 30";
cmd.Connection = conn;
conn.Open();
var count = (int)cmd.ExecuteScalar();
if (count < 0)
{
MessageBox.Show("Attenzione alcuni prodotti sono in disponibilita' limitata!");
conn.Close();
}
}
What should I do ?
Thanks

Try something like this:
using (var cmd = new OleDbCommand())
{
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select COUNT(*) from Prodotti where Disponibilta < 30";
var count = (int)cmd.ExecuteScalar();
if (count > 0)
{
MessageBox.Show("Attenzione alcuni prodotti sono in disponibilita' limitata!");
//connection.Close(); wrap connection around an using
}
}
Basically you ask to database the number of Prodotti that Disponibilta < 30, so if any you show the messagebox.
EDIT
I assume that Disponibilta is a numeric.

You shouldn't use ExecuteNonQuery() with a simple SELECT statement, SQLDataReader is quicker and the proper way to do this:
cmd.CommandText = "SELECT * FROM Prodotti WHERE Disponibilta < 30";
conn.Open();
MySqlDataReader myReader = cmd.ExecuteReader();
if(myReader.HasRows)
{
//This means you have at least one product with less than 30.
}
myReader.Close();
conn.Close();

Select keyword introduces a query, so you have to use .ExecuteReader()..ExecuteNonQuery() is used for INSERT, DELETE, UPDATE and return value is the number of rows affected.
For your situation, create a reader and check the first value
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read()
{
if (reader[0] < aValue) //make here the appropiate conversion
{
MessageBox.Show("Attenzione alcuni prodotti sono in disponibilita' limitata!");
connection.Close();
break;//maybe return?
}
}

Using C# to loop through and insert data

I have a program that has to loop through a Scenarios database, and for each while loop iteration, update a second Results database. Here's the segment of code.
public void TestScenarios(SqlConnection connection)
{
using (SqlCommand cmd = new SqlCommand("SELECT * FROM Scenarios", connection))
{
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
string Id = reader["ScenarioID"].ToString();
string Data = reader["ScenarioData"].ToString();
string Url = reader["ScenarioURL"].ToString();
webBrowser1.Navigate(Url);
InsertResults(connection, Id);
}
}
reader.Close();
}
}
public void InsertResults(SqlConnection conn, string Id)
{
using (SqlCommand cmd = new SqlCommand("INSERT INTO Results VALUES(" +
"#ResultID, #HasSucceeded, #ScenarioID, #Screenshot)", conn))
{
cmd.Parameters.AddWithValue("#ResultID", 0);
cmd.Parameters.AddWithValue("#HasSucceeded", 0);
cmd.Parameters.AddWithValue("#ScenarioID", Id);
cmd.Parameters.AddWithValue("#Screenshot", "screenshot.jpeg");
}
}
It's not working, and I'm sure I did tons of things wrong, but I'm having trouble finding direction.

Your second command is never executing. Add:
cmd.ExecuteNonQuery();

May I propose you to use SqlBulkCopy? Here is some information on how to copy two database tables , I hope you'll find it clear.
http://www.codeproject.com/Articles/18418/Transferring-Data-Using-SqlBulkCopy
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlbulkcopy%28v=vs.90%29.aspx

How can I return a single value from an SqlDataReader?

I forget to return value in single tier application.
public int Studentid()
{
try
{
SqlConnection con = new SqlConnection(connectionStr);
SqlCommand cmd = new SqlCommand("SELECT s_id FROM student where name = + ('" + Request.QueryString.ToString() + "')", con);
con.Open();
SqlDataReader dr = null;
con.Open();
dr = cmd.ExecuteReader();
if (dr.Read())
{
//Want help hear how I return value
}
con.Close();
}
catch (Exception ex)
{
throw ex;
}
}

Here is a version of your method that achieves what you're after.
public int GetStudentId()
{
var sql = string.Format("SELECT s_id FROM student where name = '{0}'", Request.QueryString);
using (var con = new SqlConnection(connectionStr))
using (var cmd = new SqlCommand(sql, con))
{
con.Open();
var dr = cmd.ExecuteReader();
return dr.Read() ? return dr.GetInt32(0) : -1;
}
}
There's no need to use try/catch when you don't do anything with the exception except re-throw (and in fact you were losing the original stack trace by using throw ex; instead of just throw;. Also, the C# using statement takes care of cleaning up your resources for you in fewer lines of code.
IMPORTANT
Passing the query string directly into SQL like that means that anyone can execute random SQL into your database, potentially deleting everything (or worse). Read up on SQL Injection.

You should use using blocks, so that you are sure that the connection, command and reader are closed correctly. Then you can just return the value from inside the if statement, and doesn't have to store it in a variable until you have closed the objects.
You only have to open the connection once.
You should use parameterised queries, instead of concatenating values into the query.
public int Studentid() {
try {
using (SqlConnection con = new SqlConnection(connectionStr)) {
using (SqlCommand cmd = new SqlCommand("SELECT s_id FROM student where name = #Name", con)) {
cmd.Parameters.Add("#Name", DbType.VarChar, 50).Value = Request.QueryString.ToString();
con.Open();
using (SqlDataReader dr = cmd.ExecuteReader()) {
if (dr.Read()) {
return dr.GetInt32(0);
} else {
return -1; // some value to indicate a missing record
// or throw an exception
}
}
}
}
} catch (Exception ex) {
throw; // just as this, to rethrow with the stack trace intact
}
}

The easiest way to return a single value is to call ExecuteScalar. You should also fix your SQL injection bug. And did you mean to encode the entire query string array, or just to pick out a single value?
public int StudentId()
{
string sql = "SELECT s_id FROM student WHERE name = #name";
using (var con = new SqlConnection(connectionStr))
{
using (var cmd = new SqlCommand(sql, con))
{
cmd.Parameters.Add("#name", DbType.VarChar, 256).Value = Request.QueryString["name"];
con.Open();
return (int)cmd.ExecuteScalar();
}
}
}

try this:
int s_id = (int) dr["s_id"];

int studId=0;
if(rdr.Read())
{
studId=rdr.GetInt32(rdr.GetOrdinal("s_id"));
}

if (dr.Read())
{
//Want help hear how i return value
int value = dr.GetInt32("s_id");
}

Like this?
public int Studentid()
{
int studentId = -1;
SqlConnection con = null;
try
{
con = new SqlConnection(connectionStr);
SqlCommand cmd = new SqlCommand("SELECT s_id FROM student where name = + ('" + Request.QueryString.ToString() + "')", con);
SqlDataReader dr = null;
con.Open();
dr = cmd.ExecuteReader();
if (dr.Read())
{
studentId = dr.GetInt32(0);
}
dr.Close();
}
catch (Exception ex)
{
throw ex;
}
finally
{
if(con != null)
con.Close();
con = null;
}
return studentId;
}