I am trying to update my database while reading data from it, but the reader gets closed and it throws the exception that it can''t read wen reader is closed. Is the update.ExecuteNonQuery() closing the reader method?
If i get rid of linescon.Close(); con.Open(); i get There is already an open DataReader associated with this Connection which must be closed first.
So how can i update my database records while keep the reading opened?
{
public class MySqlReadUpdate
{
public int Id { get; set; }
public string Notes { get; set; }
}
static void Main()
{
List<MySqlReadUpdate> dbData = new List<MySqlReadUpdate>();
var config = "server=localhost;user id=root; database=restaurants; pooling=false;SslMode=none;Pooling=True";
MySqlConnection con = new MySqlConnection(config);
MySqlDataReader reader = null;
string query = "SELECT id, notes FROM customers";
MySqlCommand command = new MySqlCommand(query, con);
con.Open();
reader = command.ExecuteReader();
while (reader.Read())
{
MySqlReadUpdate newMySqlReadUpdate = new MySqlReadUpdate();
newMySqlReadUpdate.Id = (int)reader["id"];
newMySqlReadUpdate.Notes = (string)reader["notes"];
string note = newMySqlReadUpdate.Notes;
var notesplit = note.Split(' ', '\n')[1];
dbData.Add(newMySqlReadUpdate);
Console.WriteLine(newMySqlReadUpdate.Id);
Console.WriteLine(newMySqlReadUpdate.Notes);
Console.WriteLine(note);
Console.WriteLine(notesplit);
con.Close();
con.Open();
string query2 = "UPDATE customers SET notes='" + notesplit + "' WHERE id='" + newMySqlReadUpdate.Id + "';";
MySqlCommand update = new MySqlCommand(query2, con);
update.ExecuteNonQuery();
}
con.Close();
Console.WriteLine("Finished!");
Console.Read();
}
}
}
You cannot close a connection like you are, because the data reader depends on it. Once you call con.Close you break it. That's why you see an exception the next time it gets to reader.Read().
What you want is to add MultipleActiveResultSets=True in the configuration string; however, as we discussed in the comments it's apparently still not supported in MySQL. Therefore, the answer is two connection instances.
List<MySqlReadUpdate> dbData = new List<MySqlReadUpdate>();
var config = "server=localhost;user id=root;database=restaurants;pooling=false;SslMode=none";
MySqlConnection con = new MySqlConnection(config);
MySqlConnection cmdCon = new MySqlConnection(config);
MySqlDataReader reader = null;
string query = "SELECT id, notes FROM customers";
MySqlCommand command = new MySqlCommand(query, con);
con.Open();
cmdCon.Open();
reader = command.ExecuteReader();
while (reader.Read())
{
MySqlReadUpdate newMySqlReadUpdate = new MySqlReadUpdate();
newMySqlReadUpdate.Id = (int)reader["id"];
newMySqlReadUpdate.Notes = (string)reader["notes"];
string note = newMySqlReadUpdate.Notes;
var notesplit = note.Split(' ', '\n')[1];
dbData.Add(newMySqlReadUpdate);
Console.WriteLine(newMySqlReadUpdate.Id);
Console.WriteLine(newMySqlReadUpdate.Notes);
Console.WriteLine(note);
Console.WriteLine(notesplit);
string query2 = "UPDATE customers SET notes='" + notesplit + "' WHERE id='" + newMySqlReadUpdate.Id + "';";
MySqlCommand update = new MySqlCommand(query2, cmdCon);
update.ExecuteNonQuery();
}
con.Close();
cmdCon.Close();
Console.WriteLine("Finished!");
Console.Read();
I would recommend that you also modify your code to use using statements or wrap things in try-finally blocks.
Related
I am trying to store sql data that I have for a voucher id and voucher amount into a variable and display it into a label on a click of a button.
protected void Button1_Click(object sender, EventArgs e)
{
string voucherId = String.Empty;
string voucherAmount = String.Empty;
string queryVoucherId = "select voucherid from ReturnForm where email = '" + Session["username"] + "';";
string queryVoucherAmount = "select voucheramount from ReturnForm where email = '" + Session["username"] + "';";
int index = 0;
using (SqlConnection con = new SqlConnection(str))
{
SqlCommand cmd = new SqlCommand(queryVoucherId, con);
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
while (reader.Read())
{
voucherId = reader[index].ToString();
index++;
}
}
using (SqlConnection con = new SqlConnection(str))
{
SqlCommand cmd = new SqlCommand(queryVoucherAmount, con);
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
while (reader.Read())
{
voucherAmount = reader[index].ToString();
index++;
}
}
if (txtVoucher.Text == voucherId)
{
Label3.Visible = true;
Label3.Text = voucherAmount;
}
}
When I click the button its giving me an error saying that the index is out of bounds.
Building on #JSGarcia's answer - but using parameters as one ALWAYS should - you'd get this code:
string email = Session['username'];
string query = $"SELECT voucherid, voucheramount FROM ReturnFrom WHERE Email = #email";
DataTable dt = new DataTable();
using (SqlConnection conn = new SqlConnection(connectionString))
using (SqlCommand cmd = new SqlCommand(query, conn))
using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
{
// set the parameter before opening connection
// this also defines the type and length of parameter - just a guess here, might need to change this
cmd.Parameters.Add("#email", SqlDbType.VarChar, 100).Value = email;
conn.Open();
sda.Fill(dt);
conn.Close();
}
Personally, I'd rather use a data class like
public class VoucherData
{
public int Id { get; set; }
public Decimal Amount { get; set; }
}
and then get back a List<VoucherData> from your SQL query (using e.g. Dapper):
string query = $"SELECT Id, Amount FROM ReturnFrom WHERE Email = #email";
List<VoucherData> vouchers = conn.Query<VoucherData>(query).ToList();
I'd try to avoid the rather clunky and not very easy to use DataTable construct...
I strongly recommend combining your sql queries into a single one, write it into a datatable and continue your logic from there. IMHO it is much cleaner code:
string email = Session['username'];
string query = $"SELECT voucherid, voucheramount FROM ReturnFrom where Email = '{email}'";
DataTable dt = new DataTable();
using (SqlConnection conn = new SqlConnection(connectionString))
using (SqlCommand cmd = conn.CreateCommand())
using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
{
cmd.CommandText = query;
cmd.CommandType = CommandType.Text;
conn.Open();
sda.Fill(dt);
conn.Close();
}
// Work with DataTable dt from here on
...
Well, one more big tip?
You ONLY as a general rule need a dataadaptor if you going to update the data table.
And you ONLY need a new connection object if you say not using the sql command object.
The sqlcommand object has:
a connection object - no need to create a separate one
a reader - no need to create a separate one.
Note how I did NOT create a seperate connection object, but used the one built into the command object.
And since the parameter is the SAME in both cases? Then why not re-use that too!!
So, we get this:
void TestFun2()
{
String str = "some conneciton???";
DataTable rstVouch = new DataTable();
using (SqlCommand cmdSQL =
new SqlCommand("select voucherid from ReturnForm where email = #email",
new SqlConnection(str)))
{
cmdSQL.Parameters.Add("#email", SqlDbType.NVarChar).Value = Session["username"];
cmdSQL.Connection.Open();
rstVouch.Load(cmdSQL.ExecuteReader());
// now get vouch amount
cmdSQL.CommandText = "select voucheramount from ReturnForm where email = #email";
DataTable rstVouchAmount = new DataTable();
rstVouchAmount.Load(cmdSQL.ExecuteReader());
if (rstVouch.Rows[0]["vourcherid"].ToString() == txtVoucher.Text)
{
Label3.Visible = true;
Label3.Text = rstVouchAmount.Rows[0]["voucheramount"].ToString();
}
}
}
I tried the following in SQL Server Management Studio; I can connect and run query, but not from my project
string s = "Server=LAPTOP-7J47C5JA\SQLEXPRESS;Database=Test;Trusted_Connection=True;";
string queryString = "SELECT * from tbclienti";
cn = new SQLConnection(s);
// Create the Command and Parameter objects.
SqlCommand command = new SqlCommand(queryString, cn);
cn.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Text = reader[0].ToString();
label1.Text = reader[1].ToString()+ " " + reader[2].ToString();
}
reader.Close();
cn.Close();
I posted here whole code what could look like. Try it now.
string s = #"Server=(local)\SQLEXPRESS;Database=Test;Integrated Security=SSPI;";
using(SqlConnection cn = new SqlConnection(s))
{
string queryString = "SELECT * from tbclienti";
try
{
cn.Open();
// Create the Command and Parameter objects.
SqlCommand command = new SqlCommand(queryString, cn);
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Text = reader[0].ToString();
label1.Text = reader[1].ToString()+ " " + reader[2].ToString();
}
reader.Close();
}
catch(Exception ex)
{
// see if error appear
}
finally
{
cn.Close();
}
}
I'm working on application which needs to connect to another database to get some data,
and to do that, I decided to use SqlConnection, reader etc..
And I need to execute few queries, for example first I need to get CARD ID for some user, after that I need to get some data by that CARD ID..
Here is my code:
#region Connection to another Database
SqlConnection sqlConnection1 = new SqlConnection("Data Source=ComputerOne; Initial Catalog=TestDatabase;Integrated Security=False; User ID=test; Password=test123;");
SqlCommand cmd = new SqlCommand();
SqlDataReader reader;
cmd.CommandText = "Select * From Users Where CardID=" + "'" + user.CardID + "'";
cmd.CommandType = CommandType.Text;
cmd.Connection = sqlConnection1;
sqlConnection1.Open();
reader = cmd.ExecuteReader();
string cardID = "";
string quantity="";
while (reader.Read())
{
cardID = reader["CardID"].ToString();
}
//HOW COULD I WRITE ANOTHER QUERY NOW, FOR EXAMPLE, OK I GOT CARDID NOW GIVE ME SOME OTHER THINGS FROM THAT DATABASE BY THAT cardID
//here I tried to change CommandText and to keep working with reader.. but its not working like this because its throwing me exception mention in question title.
cmd.CommandText = "Select T1.CardID, T2.Title, Sum(T1.Quantity) as Quantity From CardTransactions as T1 JOIN Adds as T2 ON T1.AddsID = T2.AddsID Where T1.CardID =" + cardID + "AND T1.Type = 1 Group By T1.CardID, T2.Title";
reader = cmd.ExecuteReader();
while (reader.Read())
{
quantity = reader["Quantity"].ToString();
}
// Data is accessible through the DataReader object here.
sqlConnection1.Close();
#endregion
So guys how could I execute few queries statemens using this example.
Thanks a lot!
Cheers
Your problem is that you are not disposing the objects you are using. For that purpose is better to always use using structure, since it will guarantee you that everithing is gonna be disposed. Try the code below:
SqlConnection sqlConnection1 = new SqlConnection("Data Source=ComputerOne; Initial Catalog=TestDatabase;Integrated Security=False; User ID=test; Password=test123;");
SqlCommand cmd = new SqlCommand();
SqlDataReader reader;
string cardID = "";
string quantity="";
using(sqlConnection1 = new SqlConnection("Data Source=ComputerOne; Initial Catalog=TestDatabase;Integrated Security=False; User ID=test; Password=test123;"))
{
sqlConnection1.Open();
using(cmd = new SqlCommand())
{
cmd.CommandText = "Select * From Users Where CardID=" + "'" + user.CardID + "'";
cmd.CommandType = CommandType.Text;
cmd.Connection = sqlConnection1;
using(reader = cmd.ExecuteReader())
{
while (reader.Read())
{
cardID = reader["CardID"].ToString();
}
} //reader gets disposed right here
} //cmd gets disposed right here
using(cmd = new SqlCommand())
{
cmd.CommandText = "Select T1.CardID, T2.Title, Sum(T1.Quantity) as Quantity From CardTransactions as T1 JOIN Adds as T2 ON T1.AddsID = T2.AddsID Where T1.CardID =" + cardID + "AND T1.Type = 1 Group By T1.CardID, T2.Title";
cmd.CommandType = CommandType.Text;
cmd.Connection = sqlConnection1;
using(reader = cmd.ExecuteReader())
{
while (reader.Read())
{
quantity = reader["Quantity"].ToString();
}
} //reader gets disposed right here
} //cmd gets disposed right here
sqlConnection1.Close();
} //sqlConnection1 gets disposed right here
The reader you opened is still active and open. And you can have just one active reader at a time. You should wrap all Sql... instances in a using to ensure they get closed properly.
using (SqlConnection connection = new SqlConnection(...))
{
using (SqlDataReader reader = cmd.ExecuteReader())
{
// the code using reader
}
}
well ... you receive the error because the used reader for the first call was not closed. You should always call the Close method when you have finished using the DataReader object insuring that the connection used by the reader is returned to the connection pool (the connection is in use exclusively by that DataReader). Partial code:
reader = cmd.ExecuteReader();
try
{
while(myReader.Read())
{
while (reader.Read())
{
cardID = reader["CardID"].ToString();
}
}
finally
{
myReader.Close();
}
...
reader = cmd.ExecuteReader();
try
{
while(myReader.Read())
{
reader = cmd.ExecuteReader();
while (reader.Read())
{
quantity = reader["Quantity"].ToString();
}
}
}
finally
{
myReader.Close();
myConnection.Close();
}
Also... as a clean code rule, separate your calls in different methods (SOLID principles)
I have the following code
public class dthvendas: System.Web.Services.WebService {
public class typVenda
{
//public string campanha;
public string id;
public string contact_moment;
public string nome;
// few more properties
}
[WebMethod][SoapDocumentMethod]
public typVenda getListaVendas(string dt_min, string dt_max)
{
//venda vendas = new List<venda>();
typVenda objVenda = new typVenda();
SqlConnection con = new SqlConnection(#"Data Source=server;Initial Catalog=database;User ID=user;password=password");
//SqlCommand cmd = new SqlCommand("SELECT * FROM dbo where contact_moment >='" + dt_min + "' AND contact_moment <DATEADD(dd, 1, '" + dt_max + "')", con);
SqlCommand cmd = new SqlCommand("SELECT * FROM dbo.vcnosadesoes_getlistavendas", con);
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
if (dr.HasRows)
{
while (dr.Read())
{
//var objVenda = new typVenda();
//objVenda.campanha = dr["id"].ToString();
objVenda.id = dr["id"].ToString();
objVenda.contact_moment = dr["contact_moment"].ToString();
objVenda.nome = dr["nome"].ToString();
objVenda.pacote = dr["pacote"].ToString();
objVenda.telefone = dr["telefone"].ToString();
objVenda.codigo_wc = dr["codigo_wc"].ToString();
//vendas.Add(objVenda);
}
dr.Close();
}
con.Close();
return objVenda;
//return vendas.ToArray();
}
The problem is that is only returning the first row instead of all rows from the table. What could be the problem any ideas?
Also when i return it says "This XML file does not appear to have any style information associated with it. The document tree is shown below." It should have a header like this:
<?xml version="1.0" encoding="UTF‐8" ?>
If you have n fetched rows available in the reader, probably you will get the last row, since the created object's properties ware over writted in each iteration of the while (dr.Read()) and finally return the latest value to the calling method. You should re-define your method to return List<typVenda>, and hence populate the list with objects constructed in each iteration. and finally return the list at the end of iteration.
Few more suggestions For you to improve the Code:
Make use of using while dealing with SqlConnection and SqlCommand; since you need not to bother about the close connection and disposing commands etc. using will take care of these things
Need not to check the reader has rows or not (if (dr.HasRows)) use while (dr.Read()) will not execute the enclosed statements if there are no rows.
Now consider the following code:
public List<typVenda> getListaVendas(string dt_min, string dt_max)
{
List<typVenda> objVendaList = new List<typVenda>();
using (SqlConnection con = new SqlConnection("connection String here"))
{
using (SqlCommand cmd = new SqlCommand("SELECT * FROM dbo.vcnosadesoes_getlistavendas", con))
{
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
var objVenda = new typVenda();
// Assign the values to the properties here
objVendaList.Add(objVenda);
}
dr.Close();
}
}
return objVendaList;
}
public List<typVenda> getListaVendas(string dt_min, string dt_max)
{
venda vendas = new List<typVenda>();
typVenda objVenda = new typVenda();
SqlConnection con = new SqlConnection(#"Data Source=server;Initial Catalog=database;User ID=user;password=password");
//SqlCommand cmd = new SqlCommand("SELECT * FROM dbo where contact_moment >='" + dt_min + "' AND contact_moment <DATEADD(dd, 1, '" + dt_max + "')", con);
SqlCommand cmd = new SqlCommand("SELECT * FROM dbo.vcnosadesoes_getlistavendas", con);
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
if (dr.HasRows)
{
while (dr.Read())
{
var objVenda = new typVenda();
//objVenda.campanha = dr["id"].ToString();
objVenda.id = dr["id"].ToString();
objVenda.contact_moment = dr["contact_moment"].ToString();
objVenda.nome = dr["nome"].ToString();
objVenda.pacote = dr["pacote"].ToString();
objVenda.telefone = dr["telefone"].ToString();
objVenda.codigo_wc = dr["codigo_wc"].ToString();
vendas.Add(objVenda);
}
dr.Close();
}
con.Close();
return vendas;
}
I need to get some mysql data into another mysql reader request anyway to workaround that I apparently can't have 2 readers open at the same time it will all end up in a datagrid
public void DBSelectPraktikanter(object sender)
{
string Command = "SELECT * FROM forlob WHERE firmaid = N'" + firmaid + "'";
MySqlConnection sqlConnection1 = new MySqlConnection(connectionString);
MySqlCommand command = new MySqlCommand(Command, sqlConnection1);
sqlConnection1.Open();
MySqlDataReader reader = command.ExecuteReader();
var items = new List<praktikanter>();
if (reader.HasRows)
{
while (reader.Read())
{
string praktikantid = String.Format("{0}", reader["praktikantid"]);
string Command2 = "SELECT * FROM praktikanter WHERE id = N'" + praktikantid + "'";
MySqlCommand command2 = new MySqlCommand(Command, sqlConnection1);
MySqlDataReader reader2 = command.ExecuteReader();
if (reader.HasRows)
{
while (reader2.Read())
{
Praktikant = String.Format("{0}", reader["Navn"]);
}
}
string Fra = String.Format("{0}", reader["fra"]);
string Til = String.Format("{0}", reader["til"]);
items.Add(new praktikanter(Praktikant, Fra, Til));
}
}
sqlConnection1.Close();
var grid = sender as DataGrid;
grid.ItemsSource = items;
}
Instead of nesting MySqlCommands and looping the first resultset to query again the database to collect all of your data you should really use one query. Also use the using-statement to ensure that the connection gets closed even on error and use sql-parameters to avoid sql-injection issues:
var items = new List<praktikanter>();
string sql = #"SELECT p.*, f. Navn
FROM praktikanter p INNER JOIN forlob f ON p.id = f.praktikantid
WHERE f.firmaid = #firmaid";
using (var con = new MySqlConnection(connectionString))
using (var command = new MySqlCommand(sql, con))
{
command.Parameters.Add(new MySqlParameter("#firmaid", MySqlDbType.VarChar).Value = firmaid);
con.Open();
using (var rd = command.ExecuteReader())
{
while (rd.Read())
{
string praktikant = rd.GetString("Navn");
string fra = rd.GetString("Fra");
string til = rd.GetString("Til");
items.Add(new praktikanter(praktikant, fra, til));
}
}
}