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Connect to database in sepaerate method of my SqlCommand

I have a form that checks whether values are in a database before adding them. Each field is in a different table, and to keep everything clean, I have a checkExists method for each field. Is there a way to have a separate method that connects to the database, so that I don't have to connect in every field method?
I'd like to do something like this so that my code is less messy:
public void SetConnection()
{
SqlConnection myConnection =
new SqlConnection("user id=[username];" +
"password=[password];" +
"server=[server];" +
"database=[db_name];");
try
{
myConnection.Open();
}
catch(Exception e)
{
Console.WriteLine("Unable to Connect");
}
}
public Boolean CheckData_Company(string[] items)
{
Class_DB set_conn = new Class_DB();
try
{
set_conn.SetConnection();
}
catch(Exception e)
{
Console.WriteLine(e.ToString());
}
//check that item does not already exist
string query_string = "SELECT * FROM CR_Company WHERE ([CompanyName] = #companyName";
SqlCommand check_Company = new SqlCommand(query_string, set_conn);
check_Company.Parameters.AddWithValue("#CompanyName", items[0]);
int CompanyExist = (int)check_Company.ExecuteScalar();
if(CompanyExist > 0)
{
return true;
}
else
{
return false;
}
}
But I get a
local variable set_conn
Argument 2: Cannot Convert from Class_DB to System.Data.SqlClient.SqlConnection
I understand the error, so what can I do to return the correct value, or do I have to establish a connection within my CheckData_Comany() method?

Your method SetConnection should be returning SqlConnection back like:
public SqlConnection SetConnection()
{
SqlConnection myConnection = new SqlConnection("user id=[username];" +
"password=[password];" +
"server=[server];" +
"database=[db_name];");
try
{
myConnection.Open();
}
catch(Exception e)
{
Console.WriteLine("Unable to Connect");
}
return myConnection;
}
and then you can have something like:
SqlConnection connection = set_conn.SetConnection();
and then pass it in SqlCommand constructor as parameter :
SqlCommand check_Company = new SqlCommand(query_string, connection);
Your complete method implementation would become :
public Boolean CheckData_Company(string[] items)
{
bool Exists = false;
Class_DB set_conn = new Class_DB();
SqlConnection connection = null;
try
{
connection = set_conn.SetConnection();
//check that item does not already exist
string query_string = "SELECT * FROM CR_Company WHERE ([CompanyName] = #companyName";
SqlCommand check_Company = new SqlCommand(query_string, set_conn);
check_Company.Parameters.AddWithValue("#CompanyName", items[0]);
int CompanyExist = (int)check_Company.ExecuteScalar();
if(CompanyExist > 0)
Exists = true;
}
catch(Exception e)
{
Console.WriteLine(e.ToString());
}
finally
{
connection.Close();
}
return Exists;
}
and important thing to note is do not forget the close the connection finally by calling connection.Close(), otherwise it might cause eating up the resources that shouldn't happen when we are done with querying the database and we should release the resources occupied.

How to insert data into two SQL Server tables in asp.net

I have two tables, the first table is Course and this table contains three columns Course_ID, Name_of_course, DeptID; and the second table is Department and it has three columns DeptID, DepName, College.
I put a GridView to display the data that I will add it. But when I write the command to insert the data in both tables the data don't add. I used this command
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
try
{
GridViewRow r = GridView1.SelectedRow;
Dbclass db = new Dbclass();
string s = "";
DataTable dt = db.getTable(s);
ddcollege.SelectedValue = dt.Rows[0]["College"].ToString();
dddept.SelectedValue = dt.Rows[1]["DepName"].ToString();
tbid.Text = r.Cells[0].Text;
tbcourse_name.Text = r.Cells[1].Text;
lblid.Text = tbid.Text;
lberr.Text = "";
}
catch (Exception ex)
{
lberr.Text = ex.Message;
}
}
protected void btadd_Click(object sender, EventArgs e)
{
try
{
if (tbid.Text == "")
{
lberr.Text = "Please input course id";
return;
}
if (tbcourse_name.Text == "")
{
lberr.Text = "Please input course name";
return;
}
string s = "Insert into Course(Course_ID,Name_of_course) values ('" + tbid.Text + "','" + tbcourse_name.Text + "')";
s = "INSERT INTO Department (DepName,College,DeptID) VALUES ('"+dddept.SelectedValue+"','"+ddcollege.SelectedValue+"','"+tbdeptID.Text+"')";
Dbclass db = new Dbclass();
if (db.Run(s))
{
lberr.Text = "The data is added";
lblid.Text = tbid.Text;
}
else
{
lberr.Text = "The data is not added";
}
SqlDataSource1.DataBind();
GridView1.DataBind();
}
catch (Exception ex)
{
lberr.Text = ex.Message;
}
}
Here is the Dbclass code:
public class Dbclass
{
SqlConnection dbconn = new SqlConnection();
public Dbclass()
{
try
{
dbconn.ConnectionString = #"Data Source=Fingerprint.mssql.somee.com;Initial Catalog=fingerprint;Persist Security Info=True;User ID=Fingerprint_SQLLogin_1;Password=********";
dbconn.Open();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
//----- run insert, delete and update
public bool Run(String sql)
{
bool done= false;
try
{
SqlCommand cmd = new SqlCommand(sql,dbconn);
cmd.ExecuteNonQuery();
done= true;
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
return done;
}
//----- run insert, delete and update
public DataTable getTable(String sql)
{
DataTable done = null;
try
{
SqlDataAdapter da = new SqlDataAdapter(sql, dbconn);
DataSet ds = new DataSet();
da.Fill(ds);
return ds.Tables[0];
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
return done;
}
}
Thank you all

The main thing I can see is you are assigning two different things to your "s" variable.
At this point db.Run(s) the value is "Insert into Department etc" and you have lost the first sql string you assigned to "s"
Try:
string s = "Insert into Course(Course_ID,Name_of_course) values ('" + tbid.Text + "','" + tbcourse_name.Text + "')";
s += "INSERT INTO Department (DepName,College,DeptID) VALUES ('"+dddept.SelectedValue+"','"+ddcollege.SelectedValue+"','"+tbdeptID.Text+"')";
Notice the concatenation(+=). Otherwise as mentioned above using a stored procedure or entity framework would be a better approach. Also try to give your variables meaningful names. Instead of "s" use "insertIntoCourse" or something that describes what you are doing

When a value is inserted into a table(Table1) and and value has to be entered to into another table(Table2) on insertion of value to Table1, you can use triggers.
https://msdn.microsoft.com/en-IN/library/ms189799.aspx

"tbdeptID.Text" is giving you the department Id only right? You should be able to modify your first statement
string s = "Insert into Course(Course_ID,Name_of_course,) values ('" + tbid.Text + "','" + tbcourse_name.Text + "',)";
Please start running SQL Profiler, it is a good tool to see what is the actual query getting executed in server!

c# mysql unable to output query to a textbox

here is my code:
private void searchInDatabase()
{
MySqlConnection c = new MySqlConnection("datasource=localhost; username=root; password=123456; port=3306");
MySqlCommand mcd;
MySqlDataReader mdr;
String query;
try
{
c.Open();
query = "SELECT * FROM test.classmates WHERE first_name ='"+searchName.Text+"'";
mcd = new MySqlCommand(query, c);
mdr = mcd.ExecuteReader();
if(mdr.Read())
{
firstName.Text = mdr.GetString("first_name");
middleName.Text = mdr.GetString("middle_name");
lastName.Text = mdr.GetString("last_name");
age.Text = mdr.GetString("age");
}
else
{
MessageBox.Show("Result Not Found");
}
}
catch(Exception error)
{
MessageBox.Show("Error: "+error.Message);
}
finally
{
c.Close();
}
}
I would like to ask for a help if I have missed on anything or I am doing it wrong. If you have free time, I will much appreciate it if you will comment the perfect way to do I implement this problem: I want to get data from MySQL then put it in a textbox.

According to MSDN you need to pass the column number as parameter
public override string GetString(int i)
So try to pass the column number (starts from 0) of your column name. Assuming the first_name is the first column of your table then
firstName.Text = mdr.GetString(0);
UPDATE
Try to use MySqlConnectionStringBuilder
MySqlConnectionStringBuilder conn_string = new MySqlConnectionStringBuilder();
conn_string.Server = "serverip/localhost";
conn_string.UserID = "my_user";
conn_string.Password = "password";
conn_string.Database = "my_db";
MySqlConnection conn = new MySqlConnection(conn_string.ToString();

First of all look at this sample of connection string and change your connection string:
'Server=myServerAddress;Port=1234;Database=myDataBase;Uid=myUsername;Pwd=myPasswor;'
If connection is OK send erorr message or full exception.

OpenFileDialog loop application only after a DB query

I have an difficult situation :
this is my form :
the first button '...' is a btnAllegato. Code :
private void btnAllegato_Click(object sender, EventArgs e)
{
try
{
using (OpenFileDialog openFileDialog1 = new OpenFileDialog())
{
string path = string.Empty;
openFileDialog1.Title = "Seleziona richiestaIT (PDF)..";
openFileDialog1.Filter = ("PDF (.pdf)|*.pdf");
openFileDialog1.FilterIndex = 1;
openFileDialog1.FileName = "";
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
//salva l'intero path
path = openFileDialog1.FileName;
//nome file + estensione
string temp = openFileDialog1.SafeFileName;
//elimina l'estensione del file con IgnoreCase -> case Unsensitive
temp = Regex.Replace(temp, ".pdf", " ", RegexOptions.IgnoreCase);
//datatime + replace
string timenow = System.DateTime.Now.ToString();
//replace data da gg//mm/aaaa ss:mm:hh -----> ad gg-mm-aaaa_ss-mm-hh
timenow = timenow.Replace(":", "-").Replace("/", "-");//.Replace(" ", " ");
_url = #"\\192.168.5.7\dati\SGI\GESTIONE IT\RichiesteIT\" + temp + timenow + ".pdf";
System.IO.File.Copy(path, _url);
}
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
after i have a button Inserisci >> (btnInserisci)
with this button i Create a DB Query to insert data...
private void btnInserisci_Click(object sender, EventArgs e)
{
try
{
if ((_IDRichiedente != -1) && (_data != string.Empty) && (_url != string.Empty))
{
MessageBox.Show(_url);
QueryAssist qa = new QueryAssist();
string query = "INSERT INTO RICHIESTA_IT(ID_Risorsa, descrizione_richiesta, modulo_pdf, data_richiesta) VALUES('" + _IDRichiedente + "', '" + txtBreveDescrizione.Text + "', '" + _url + "', '" + _data + "');";
MessageBox.Show(query);
qa.runQuery(query);
else
{
MessageBox.Show("Selezionare il richiedente,data o allegato!");
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
where
private int _IDRichiedente = -1;
private string _data = String.Empty;
private string _url = string.Empty;
is a fields of class.
QueryAssist is my class that connect, run query and disconnect to Access DB.
code :
class QueryAssist
{
System.Data.OleDb.OleDbConnection _OleDBconnection;
public QueryAssist()
{
this._OleDBconnection = null;
}
private bool connectionDB()
{
string connection = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=\"\\\\192.168.5.7\\dati\\Scambio\\Sviluppo\\Impostazioni temporanea db Censimento\\CensimentoIT.accdb\"";
try
{
_OleDBconnection = new System.Data.OleDb.OleDbConnection(connection);
_OleDBconnection.Open();
return true;
}
catch(Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
return false;
}
}
private void disconnectDB()
{
try
{
_OleDBconnection.Close();
}
catch (Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
}
}
public System.Data.DataTable runQuery(string query)
{
try
{
if (connectionDB())
{
System.Data.DataTable dataTable = new System.Data.DataTable();
System.Data.OleDb.OleDbCommand sqlQuery = new System.Data.OleDb.OleDbCommand(query, _OleDBconnection);
System.Data.OleDb.OleDbDataAdapter adapter = new OleDbDataAdapter(sqlQuery);
adapter.Fill(dataTable);
disconnectDB();
return dataTable;
}
}
catch(Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
}
return null;
}
public int countRowsQueryResult(string query)
{
try
{
if (connectionDB())
{
System.Data.DataTable dataTable = new System.Data.DataTable();
System.Data.OleDb.OleDbCommand sqlQuery = new System.Data.OleDb.OleDbCommand(query, _OleDBconnection);
System.Data.OleDb.OleDbDataAdapter adapter = new OleDbDataAdapter(sqlQuery);
adapter.Fill(dataTable);
disconnectDB();
return dataTable.Rows.Count;
}
}
catch (Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
}
return -1;
}
}
At firt time ... The application work good. I selected a file and other data and I click on button 'Inserisci>>' and all working good.
Next step when i want to insert other data ... when i click on '...' button for attachment a file i have the loop OpenFileDialog
To close, i must kill the process.
I have [STAThread] set on main of the program.
Connect to NAS isn't a problem ... I have try in local .. and i have the same problem..
If i click on btn '...' to OpenFileDialg then not click on button 'Inserisci>>'
OpenFileDialog work good for all time ...
But if i click on button 'Inserisci>>' on the next click on button '...' to OpenFileDialog application loop..
Sorry for bad english ..I'm here for clarification

The use of the runQuery method with an INSERT statement could be the cause of your problems. To insert a record you should use an OleDbCommand with the ExecuteNonQuery. A Fill method is used to fill a DataTable.
The fact that the record is inserted anyway happens because the underlying command used to fill the DataTable (ExecuteReader) ignores its sql command text and executes what you have passed. However after that the Fill method expects to fill a DataTable and not having a select statement could be potentially the cause of your problems.
I would use a different method when you need to Update/Delete or Insert new data
public int runNonQuery(string query)
{
try
{
if (connectionDB())
{
OleDbCommand sqlQuery = new OleDbCommand(query, _OleDBconnection);
int rows = sqlQuery.ExecuteNonQuery();
disconnectDB();
return rows;
}
}
catch(Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
return -1;
}
}
There are other problems in your code and are all connected to the way in which you concatenate together the string to form an sql statement. This is know as the worst practice possible with database code. If you take a bit of your time to investigate how to write a parameterized query you will avoid a lot of future problems.

nested data reader issue mysql c#

I have written a custom class to handle database queries to a remote and local MySQL database, however when I do a nested loop I receive the below error:
MySql.Data.MySqlClient.MySqlException was unhandled
Message=There is already an open DataReader associated with this Connection which must be closed first.
Source=MySql.Data
ErrorCode=-2147467259
Number=0
My class currently looks like this
public class MySQLManager
{
private MySqlConnection _MySQLRemoteConnection { get; set; }
public void setup(string remoteUser, string remotePass, string remoteServerAddress, string remoteDb, string localUser, string localPass, string localServerAddress, string localDb)
{
_remote_server_address = remoteServerAddress;
_remote_database = remoteDb;
_remote_username = remoteUser;
_remote_password = remotePass;
}
public void connect()
{
try
{
_MySQLRemoteConnection = new MySqlConnection() { ConnectionString = string.Format("server={0};database={1};uid={2};password={3};", _remote_server_address, _remote_database, _remote_username, _remote_password) };
_MySQLRemoteConnection.Open();
_RemoteConnection = true;
}
catch (MySqlException ex)
{
_RemoteConnection = false;
}
}
public MySqlCommand run(string query, List<MySqlParameter> dbparams = null)
{
connect();
MySqlCommand sql = getConnection().CreateCommand();
sql.CommandText = query;
if (dbparams != null)
{
if (dbparams.Count > 0)
{
sql.Parameters.AddRange(dbparams.ToArray());
}
}
//disconnect();
return sql;
}
public MySqlDataReader fetch(MySqlCommand cmd)
{
//connect();
var t = cmd.ExecuteReader();
//disconnect();
return t;
}
And the code that I'm running to create the error, now I understand I can do the below example in a single query, this is an EXAMPLE query to re-create the error, writing it into a single query will not work with live examples.
query = "SELECT field1 FROM tmp WHERE field1 < 3";
using (var sql = db.run(query))
{
txtResponse.Text += "Query ran" + nl;
using (var row = db.fetch(sql))
{
txtResponse.Text += "Query fetched" + nl;
db.connect();
while (row.Read())
{
txtResponse.Text += "Row : " + row[0].ToString() + nl;
query = "SELECT val1 FROM tmp2 WHERE field1 = '" + row[0].ToString() + "'";
//db.disconnect();
using (var sql2 = db.run(query))
{
txtResponse.Text += "Query ran" + nl;
db.disconnect();
using (var row2 = db.fetch(sql))
{
txtResponse.Text += "Query fetched" + nl;
db.connect();
while (row.Read())
{
txtResponse.Text += " Val : " + row2[0].ToString() + nl;
}
}
}
}
}
}
So how would I go about getting the second loop to work?

For SQL Server, you could use MultipleActiveResultSets=true on connection string, but this most likely won't work for MySQL.
The other option is to use 2 connections, one for each data reader.