I've just read all the answers about the same problem but they have not helped.
This is a part of my c# code that is too long. It has a lot of SQLConnections and 2 timers.
Indirizzo nuovoInd = new Indirizzo();
SqlConnection cn = new SqlConnection(nuovoInd.OttieniIP());
string strSql = "INSERT INTO Pietanze(nome,prezzo,ingredienti,cod_cat) VALUES ('"+nome+"','"+prezzo+"','"+ingredienti+"','"+contCat+"')";
SqlCommand cmd = new SqlCommand(strSql, cn);
cn.Open();
SqlDataReader dr = cmd.ExecuteReader();
or
public static float GetCoperti(int codOrdine)
{
float copertiTot = 0;
List<Ordine> ordini = new List<Ordine>();
VisualizzaOrdini.Form1.Indirizzo nuovoInd = new VisualizzaOrdini.Form1.Indirizzo();
SqlConnection cn = new SqlConnection(nuovoInd.OttieniIP());
string strSql = "SELECT codo,tavolo,InsertDate,nCoperti,costoCoperti FROM Ordini, Riga_Ordine, Coperti where codo=cod_or and cod_or = '"+ codOrdine + "' ORDER BY InsertDate DESC";
SqlCommand cmd = new SqlCommand(strSql, cn);
cn.Open();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
Ordine currO = new Ordine();
currO.Data = Convert.ToDateTime(dr["InsertDate"]);
currO.Coperti = (int)dr["nCoperti"];
currO.PrezzoCoperto = Convert.ToSingle(dr["costoCoperti"]);
currO.Tavolo = dr["tavolo"].ToString();
currO.Codice = (int)dr["codo"];
copertiTot = (currO.PrezzoCoperto * Convert.ToSingle(currO.Coperti));
ordini.Add(currO);
}
return copertiTot;
}
I'm struggling with the fact that the code is throwing an OutOfMemoryException. What might be causing this? How do I resolve it?
It may be the problem that you are not Closing your SqlDataReader object after fetching records, You have to close it explicitly.
dr.Close();
And also, Close your connection after closing reader, or use using block as suggested by Habib.
cn.Close();
First, having your database connection open for the full execution of code is bad practice. Assign the execute statement to some DataTable. It will provide you the local copy of the database. It's also more convenient to process and you surely don't get out of memory exceptions.
Datatable DTab = cmdexecuteReader();
DataSet DSet = cmdexecuteReader();
Both Will give you expectedd results always.
Related
I have 02 combo box as shown [Combo Boxes]
When i move back and forth for selection of items b/w Combo Boxes(Category and Model No.) i get the following error
enter image description here
My C# sharp code is given below
try
{
con.Open();
string CmdString = "select ProductID from Product where ModelNo='" + comboModel.SelectedItem.ToString() + "'";
SqlCommand cmd = new SqlCommand(CmdString, con);
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt1 = new DataTable("Product");
sda.Fill(dt1);
foreach (DataRow dr in dt1.Rows)
{
txtProductID.Text = dr["ProductID"].ToString();
}
con.Close();
}
catch (Exception exp)
{
MessageBox.Show(exp.ToString());
con.Close();
}
Get rid of con.Open();. Obviously the connection was already open from an earlier operation somewhere else or a prior run of this code.
That being said, you should probably not be keeping connections open unless you need them, because you run the risk that they aren't ever closed properly. You should use the disposable pattern, like this:
using (var con = new SqlConnection(myConnStr))
{
// do your query, etc.
}
This will automatically close the connection and dispose of the resources.
Your connection is opened somewhere else. Try putting it into using block, this way it will be disposed of automatically and is best practice for connections:
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
string CmdString = "select ProductID from Product where ModelNo='" +
comboModel.SelectedItem.ToString() + "'";
SqlCommand cmd = new SqlCommand(CmdString, connection);
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dt1 = new DataTable("Product");
sda.Fill(dt1);
foreach (DataRow dr in dt1.Rows)
{
txtProductID.Text = dr["ProductID"].ToString();
}
}
I'm trying to search my local database table and simply display all it's columns.
I start my sending in
SearchID("1234");
My code so far:
private static void SearchID(string CostumerID)
{
string conStr = #"Data Source = C:\Users\secwp_000\documents\visual studio 2012\Projects\Module5\Module5\Orderdatabase.sdf";
DataSet ds = new DataSet();
SqlCeConnection con = new SqlCeConnection(conStr);
SqlCeCommand cmd = new SqlCeCommand("SELECT * FROM [Order]", con);
SqlCeDataReader dr = cmd.ExecuteReader();
SqlCeDataAdapter adapt = new SqlCeDataAdapter(cmd);
adapt.Fill(ds, "Order");
while (dr.Read())
{
string str = (string)dr[1];
if (str == CostumerID)
{
Console.WriteLine(str);
}
}
}
Where am I thinking wrong?
It stops on
SqlCeDataReader dr = cmd.ExecuteReader();
saying i don't have a connection. But just sounds wierd, because I've just had connection..
You have to open connection using
If(con.state.toString()=="closed")
con.open();
I observe a fault in your query why are you compare your result after fetch from database.you can directly filter in SQL query
Select * from order where table.customer_Id = customerId
You have a connection but you haven't opened it yet:
con.Open();
adapt.Fill(ds, "Order");
con.Close();
In addition you should use using statements for disposable objects like SqlConnection and SqlCommand to make sure they will be disposed properly:
using(SqlCeConnection con = new SqlCeConnection(conStr))
using(SqlCeCommand cmd = new SqlCeCommand("SELECT * FROM [Order]", con))
{
}
I feel so stupid for not seeing this, haha. And it worked! But it wont display anything from the table,
while (dr.Read())
{
string str = (string)dr[1];
if (str == CostumerID)
{
Console.WriteLine(str);
}
}
Following instructions given to me, there is nothing wrong with this code, and it could display Order with costumerID 1234.
I have created an Entity Framework application to retrieve Database values but i want to show them in individual labels instead of a gridview??
EmployEntities2 fd = new EmployEntities2();
int idToupdate = Convert.ToInt32(TextBox1.Text);
var jj = (from bn in fd.Contacts
where bn.Id == idToupdate
select bn);
GridView1.DataSource = jj;
GridView1.DataBind();
Established a connection
SqlConnection con = new SqlConnection("CONNECTION_STRING);
SqlCommand cmd = new SqlCommand();
and then,
cmd.CommandText = "select * from table where Condition ;
cmd.Connection = con
Label1.text = ((string)cmd.ExecuteScalar());
Try this one..
You should use SQLDataReader class. Base on what type of data you have in structure you should call a different method of the SQLDataReader object. For example, if you need to retrieve an integer value and display it in a label, this is the code sinppet to do it:
string queryString = "SELECT integer_value FROM table_name";
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(queryString, connection);
connection.open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
label1.Text = reader.getSqlInt32(0).ToString();
}
reader.close();
}
This is the best I can do since you didn't provide additional info.
Check out this link for info on SqlDataReader class: SqlDataReader reference
I have the following:
String sql = "SELECT * FROM Temp WHERE Temp.collection = '" + Program.collection + "'";
SqlConnection conn = new SqlConnection(connString);
SqlCommand cmd = new SqlCommand(sql, conn);
Program.defaultCollection = (String)cmd.ExecuteScalar();
And I want to get the second column after executing the statement. I know it will return only one row with two columns
I have read online that I will have to read each row of the result, is there any other way?
ExecuteScalar gets the first column from the first row of the result set. If you need access to more than that you'll need to take a different approach. Like this:
DataTable dt = new DataTable();
SqlDataAdapater sda = new SqlDataAdapter(sql, conn);
sda.Fill(dt);
Program.defaultCollection = dt.Rows[0]["defaultCollection"];
Now, I realize that the field name may not be defaultCollection, but you can fill that in.
From the MSDN documentation for ExecuteScalar:
Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.
Now, as a final bit of advice, please wrap all ADO.NET objects in a using statement. Like this:
using (SqlConnection conn = new SqlConnection(connString))
using (SqlDataAdapter sda = new SqlDataAdapter(sql, conn))
{
DataTable dt = new DataTable();
sda.Fill(dt);
// do something with `dt`
}
this will ensure they are properly disposed.
And I want to get the second column after executing the statement
It is not possible with execute scalar.
is there any other way
You have 2 options here either to use SqlDataAdapter or SqlDataReader.
For you using DataReader is a recommended approach as you don't need offline data or do other worh
by using SqlDataAdapter
using (SqlConnection c = new SqlConnection(
youconnectionstring))
{
c.Open();
/
using (SqlDataAdapter a = new SqlDataAdapter(sql, c))
{
DataTable t = new DataTable();
a.Fill(t);
if(t.Rows.Count > 0)
{
string text = t.Rows[0]["yourColumn"].ToString();
}
}
}
by using DataREader
using (SqlConnection connection =
new SqlConnection(connectionString))
{
SqlCommand command =
new SqlCommand(sql, connection);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
//read data here
string text = reader.GetString(1)
}
reader.Close();
}
SqlCommand.ExecuteScalar() can be used only when the result have just one row and one column.
If you need more than one column to be returned, you should use something like this:
String sql = "SELECT * FROM Temp WHERE Temp.collection = '" + Program.collection + "'";
SqlConnection conn = new SqlConnection(connString);
using(SqlCommand cmd = new SqlCommand(sql, conn))
{
using(SqlDataReader rdr = cmd.ExecuteReader())
{
if(rdr.Read())
{
Program.defaultCollection = (String)rdr["Column1"];
Program.someOtherVar = (String)rdr["Column2"];
}
}
rdr.Close();
}
That will be the fastest way.
You can use a DataReader and read only the first column like:
IDataReader cReader = cmd.ExecuteReader();
if(cReader.Read())
{
string cText = cReader.GetString(1); // Second Column
}
ExecuteScalar only returns one value. You have to make sure your query only returns that value.
String sql = "SELECT temp.defaultCollection FROM Temp WHERE Temp.collection = '" + Program.collection + "'";
On a side note, read on SqlParameter. You don't want to concatenate values like that, you'll have a problem when the collection property contains a quote.
In my code below, the cmdquery works but the hrquery does not. How do I get another query to populate a grid view? Do I need to establish a new connection or use the same connection? Can you guys help me? I'm new to C# and asp. Here's some spaghetti code I put together. It may all be wrong so if you have a better way of doing this feel free to share.
if (Badge != String.Empty)
{
string cmdquery = "SELECT * from Employees WHERE Badge ='" + Badge + "'";
string hrquery = "SELECT CLOCK_IN_TIME, CLOCK_OUT_TIME FROM CLOCK_HISTORY WHERE Badge ='" + Badge + "'";
OracleCommand cmd = new OracleCommand(cmdquery);
cmd.Connection = conn;
cmd.CommandType = CommandType.Text;
conn.Open();
OracleDataReader reader = cmd.ExecuteReader();
while (reader.Read())
{
this.xUserNameLabel.Text += reader["EMPLOYEE_NAME"];
this.xDepartmentLabel.Text += reader["REPORT_DEPARTMENT"];
}
OracleCommand Hr = new OracleCommand(hrquery);
Hr.Connection = conn;
Hr.CommandType = CommandType.Text;
OracleDataReader read = Hr.ExecuteReader();
while (read.Read())
{
xHoursGridView.DataSource = hrquery;
xHoursGridView.DataBind();
}
}
conn.Close();
Your data access code should generally look like this:
string sql = "SELECT * FROM Employee e INNER JOIN Clock_History c ON c.Badge = e.Badge WHERE e.Badge = #BadgeID";
using (var cn = new OracleConnection("your connection string here"))
using (var cmd = new OracleCommand(sql, cn))
{
cmd.Parameters.Add("#BadgeID", OracleDbType.Int).Value = Badge;
cn.Open();
xHoursGridView.DataSource = cmd.ExecuteReader();
xHoursGridView.DataBind();
}
Note that this is just the general template. You'll want to tweak it some for your exact needs. The important things to take from this are the using blocks to properly create and dispose your connection object and the parameter to protect against sql injection.
As for the connection question, there are exceptions but you can typically only use a connection for one active result set at a time. So you could reuse your same conn object from your original code, but only after you've completely finished with it from the previous command. It is also okay to open up two connections if you need them. The best option, though, is to combine related queries into single sql statement when possible.
I'm not even going to get into how you should be using usings and methods :p
if (Badge != String.Empty)
{
string cmdquery = "SELECT * from Employees WHERE Badge ='" + Badge + "'";
string hrquery = "SELECT CLOCK_IN_TIME, CLOCK_OUT_TIME FROM CLOCK_HISTORY WHERE Badge ='" + Badge + "'";
OracleCommand cmd = new OracleCommand(cmdquery);
cmd.Connection = conn;
cmd.CommandType = CommandType.Text;
conn.Open();
OracleDataReader reader = cmd.ExecuteReader();
while (reader.Read())
{
this.xUserNameLabel.Text += reader["EMPLOYEE_NAME"];
this.xDepartmentLabel.Text += reader["REPORT_DEPARTMENT"];
}
OracleCommand Hr = new OracleCommand(hrquery);
Hr.Connection = conn;
Hr.CommandType = CommandType.Text;
OracleDataReader read = Hr.ExecuteReader();
//What's this next line? Setting the datasource automatically
// moves through the data.
//while (read.Read())
//{
//I changed this to "read", which is the
//datareader you just created.
xHoursGridView.DataSource = read;
xHoursGridView.DataBind();
//}
}
conn.Close();