Develop Reference

memory low error after caling database class method

I have bellow class in my project that can help me to run SQL commands directly. in my computer it works fine. but when I published to web server after about 5 or 6 times that I called in page I got memory low error. that error cleaned after about 20 minutes. but it happens again and again.
using System;
using System.Linq;
using System.Net;
using System.Net.Mail;
using System.Data;
using System.Data.Linq;
using System.Data.SqlClient;
using System.Data.OleDb;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Globalization;
public class FirstClass
{
SqlConnection con;
public SqlCommand cmd;
DataTable dt;
SqlDataAdapter da;
public FirstClass()
{
con = new SqlConnection(ConfigurationManager.ConnectionStrings["WebSiteConnectionString"].ConnectionString);
cmd = new SqlCommand();
dt = new DataTable();
cmd.Connection = con;
da = new SqlDataAdapter(cmd);
}
public DataTable dbSelect(string sql)
{
DataTable dttt = new DataTable();
try
{
cmd.CommandText = sql;
con.Open();
da.Fill(dt);
con.Close();
return dt;
}
catch
{
return dttt;
}
}
public void exeSp(string spName)
{
con.Open();
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = spName;
cmd.ExecuteNonQuery();
con.Close();
}
public void exeSqlCmd(string sql)
{
try
{
cmd.CommandText = sql;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
catch { }
}
}
This mostly happens when I use the first method. Of course, the number of records that are fetched is also important. The higher the number of records fetched, the faster the memory shortage error occurs. But after about 20 minutes, all the bugs will be fixed automatically and I can run the code again. But unfortunately I get the same error message again. Please help.

The code in the question has several issues. I will only explicitly mention some issues related to use of classes in System.Data.SqlClient, and not mention general issues, though the code shown here solves many of the general issues, but not all.
The classes SqlConnection, SqlCommand, SqlDataAdapter, SqlDataReader and so on, are lightweight, and should be created and released in the innermost scope possible. There is nothing to gain by trying to reuse these by holding on to them across queries. They also need to be properly managed with regards to memory use as well as resource use, not only when execution follows the success path, but also when errors arise. This can be achieved as follows.
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
public static class FirstClass
{
private static string connectionString =
ConfigurationManager.ConnectionStrings["WebSiteConnectionString"].ConnectionString;
private static SqlConnection GetConnection()
{
return new SqlConnection(connectionString);
}
public static DataTable DbSelect(string sql)
{
using (var con = GetConnection())
{
using (var cmd = new SqlCommand(sql, con))
{
using (var adapter = new SqlDataAdapter(cmd))
{
try
{
DataTable result = new DataTable();
adapter.Fill(result);
return result;
}
catch
{
return null;
}
}
}
}
}
public static void ExeSp(string spName)
{
using (var con = GetConnection())
{
using (var cmd = new SqlCommand())
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = spName;
cmd.ExecuteNonQuery();
}
}
}
public static void ExeSqlCmd(string sql)
{
using (var con = GetConnection())
{
using (var cmd = new SqlCommand(sql, con))
{
try
{
cmd.ExecuteNonQuery();
}
catch
{
}
}
}
}
}
The class has been made static, which makes sure all memory and resource management now takes place within each single method. We no longer rely on knowing how the class itself is used elsewhere in order to understand how things work. Within the methods, use of using now clearly tells us how resources, including memory, is allocated and deallocated. We can see that everything is properly disposed, so that there is no longer any way that any resource can be lying around between database calls, whether there's success or error in calls. In the DbSelect method, the DataTable is created as close to its point of use as possible, so that we easily see what it's doing.
It is not clear what the intention of having one local and one class level DataTable was in the original code, which returns one or the other - likely just a temporary glitch while experimenting - but in this new version the caller is responsible for disposing the returned result after use. An alternative is possibly to have the caller offer a DataTable to fill in, if that's easier for the caller. If so, just clear the table before filling.
When it comes to error handling, it can be improved, but I won't go into that.
This code compiles, but I have not verified that it actually works. My intention is to show how to organize these kinds of database calls in general, and you can work on fixing any error I may have overlooked from there on.

C# Error Selecting Table in OleDbCommand ...*LIBL not found

I'm trying to make a connection to a DB2 Database sitting on our AS400 (ISeries). I can connect to is successfully using the connection string but once I try to access the Tables I get this error: CPF9812: File SELECT in library *LIBL not found.
At this point I'm just trying to see if i can access the data in the table GLPCT.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.OleDb;
using System.Data;
namespace Testing_Connection_to_GLDBFA
{
class Program
{
static void Main(string[] args)
{
string connectionstring = "Provider=IBMDARLA.DataSource.1;Data Source=INFINIUM;Persist Security Info=True;Password=MyPassword;User ID=UserID;Initial Catalog=S06947A4;Default Collection=GLDBFA";
string querySTring = "";
DataTable schema;
int i = 0;
using( OleDbConnection cn = new OleDbConnection(connectionstring))
{
querySTring = "SELECT * FROM GLPCT";
OleDbCommand command = new OleDbCommand(querySTring, cn);
cn.Open();
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine(reader[0].ToString());
i++;
if (i == 20)
break;
}
cn.Close();
}
}
}
}
Any help or guidance is greatly appreciated.
Thanks in advance.

I'd expect to see the following error:
CPF9812: File GLPCT in library USERID not found.
As by default when using SQL naming the system will implicitly qualify unqualified table names with the user ID. For details, see here
It appears you are using an OLE DB provider instead of the .NET provider
If you want to use the library list, you'll need use system naming and ensure that the library list is configured on the connection.
For the OLEDB providers, you want to set the Library List and Naming Convention
<connection>.Open('Provider=IBMDA400;Data Source=SystemA;Library List=lib1,lib2, *USRLIBL;Naming Convention=1', 'Userid', 'Password');
For .NET provider, it's LibraryList and Naming properties.
Lastly, if you want to stay with the OLE DB provider, you might consider using the IBMDASQL instead of the IBMDARLA one.

removing form from c# code?

I'm extremely new to C# and programming anything except for SQL. I've gotten the below code to happen on a Form and on a button click. If I wanted to just make this run on open, how would I do that? I'm very new to C# as you can tell (just started today learning it but its pretty exciting!)
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Oracle.DataAccess.Client; // ODP.NET Oracle managed provider
using Oracle.DataAccess.Types;
namespace OraTrigger
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
string oradb = "Data Source=OMP1;User Id=user;Password=pass;";
OracleConnection conn = new OracleConnection(oradb); // C#
conn.Open();
OracleCommand cmd = new OracleCommand();
cmd.Connection = conn;
cmd.CommandText = "SELECT cast(Count(*) as varchar(20)) as trig FROM ZDMSN.TRIGGER_TEST";
//cmd.CommandType = CommandType.Text;
OracleDataReader dr = cmd.ExecuteReader();
dr.Read();
int cnt;
if (int.TryParse(dr.GetString(0), out cnt))
{
if (cnt > 0)
{
System.Diagnostics.Process.Start(#"C:\testfile.bat");
}
}
cmd.CommandText = "TRUNCATE TABLE ZDMSN.TRIGGER_TEST";
conn.Dispose();
}
}
}

If you need to run your code as a scheduled task then a command line application is more suitable.
Just create a new project and select Console Application.
Then move all of your button click code inside the Main method written for you by the Visual Studio IDE.
Rembember to set the references to the Oracle ODP.NET library and import the relevant using statements
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Oracle.DataAccess.Client; // ODP.NET Oracle managed provider
using Oracle.DataAccess.Types;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
string oradb = "Data Source=OMP1;User Id=user;Password=pass;";
using(OracleConnection conn = new OracleConnection(oradb))
using(OracleCommand cmd = new OracleCommand("SELECT Count(*) as trig FROM ZDMSN.TRIGGER_TEST", conn))
{
conn.Open();
int cnt = (int)cmd.ExecuteScalar();
if (cnt > 0)
{
System.Diagnostics.Process.Start(#"C:\testfile.bat");
cmd.CommandText = "TRUNCATE TABLE ZDMSN.TRIGGER_TEST";
cmd.ExecuteNonQuery();
}
}
}
}
}
I have also revised your code to get a single value from the database. For this case is enough to use the Command.ExecuteScalar method that returns the first column of the first row obtained from your sql command text. Because the count(*) should Always return a single row you could easily cast the return value of ExecuteScalar to your record count variable.
EDIT I have added the logic to TRUNCATE the table involved. Please pay attention that you should use the code provided here. Your code will probably fail because you have an open DataReader and when a DataReader is open you cannot execute other commands (This is true for SqlServer without Multiple Active Result Sets enabled, I really don't know if this rules applies also to the Oracle NET Provider)

Subscribe to Shown or Load event of form and move your code to that event handler.
Form.Shown Event Occurs whenever the form is first displayed.
Form.Load Event Occurs before a form is displayed for the first time.
Also I suggest to extract your code to some Data Access related class, or at least to separate method. And call that method from event handler.

Why won't C# show the table

I'm using Visual Web Developer 2010 Express and SQL Server 2008 R2 Management Studio Express
Hey guys,
Pretty new at C# here. I'm trying to follow this C# ADO.NET tutorial (currently on step 2), and I'm stumped. I'm following all the steps, and everything makes sense to me in it, but whenever I try to debug, it does not show anything (in the sense of the c# methods not printing out a table from Northwind database onto my webpage) in WebApplication1's Default.aspx page.
For a while, I thought it was my connection string, conn, and I wasn't naming the "Data Source" attribute, which from my understanding is the name of the server I'm trying to connect to. It is all on a local machine, and I'm putting the correct server name.. I think. Server name is AZUES-221\JDOESQLSERVER
I'm properly escaping the backward slash, but I still don't know. Is there something in my coding that's flawed? Please help!
C# code
using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.Services;
namespace WebApplication1
{
public partial class SqlConnectionDemo : System.Web.UI.Page
{
protected void Main(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection("Data Source=AZUES-221\\JDOESQLSERVER; Initial Catalog=Northwind; Integrated Security=SSPI");
SqlDataReader rdr = null;
try
{
conn.Open();
SqlCommand cmd = new SqlCommand("SELECT * FROM Customers", conn); //passed the connection
rdr = cmd.ExecuteReader(); // get query results
while (rdr.Read()) //prints out whatever was
{ Console.WriteLine(rdr[0]); }//selected in the table
}
finally
{
if (rdr != null)// closes
{ rdr.Close(); }// the reader
if (conn != null)//closes
{ conn.Close(); }// the connection
}
}
}
}
Thanks in advance

As your example seems to be a WebProject try to put your code within Page_Load eventHandler. Afterwards you should try to print your data to the Debug window or to a control within your webPage.
using System;
using System.Data;
// and all the others ...
namespace WebApplication1
{
public partial class SqlConnectionDemo : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection("Data Source=AZUES-221\\JDOESQLSERVER; Initial Catalog=Northwind; Integrated Security=SSPI");
SqlDataReader rdr = null;
try
{
conn.Open();
SqlCommand cmd = new SqlCommand("SELECT * FROM Customers", conn);
rdr = cmd.ExecuteReader(); // get query results
while (rdr.Read()) //prints out whatever was
{
System.Diagnostics.Debug.WriteLine(rdr[0]); // or on the other hand
lblOutput.Text += rdr[0]; // as a "quick and dirty" solution!
}
}
finally
{
if (rdr != null)// closes
{ rdr.Close(); }// the reader
if (conn != null)//closes
{ conn.Close(); }// the connection
}
}
}
}
You may it find very useful to have a look at databound controls or just use another type of project (eg winForm, console, ...)

Create a Console application instead of the Web Application you have created.
Otherwise you will run into similar issues considering you are new to C# (or Visual Studio in general) AND considering the rest of the tutorial uses Console.WriteLine heavily.
Then you can use the same code as shown in the tutorial.
Additonally if you are concerned about the slash in the database server (it is a database server instance), you may wanna try this:
SqlConnection conn = new SqlConnection(#"Server=AZUES-221\JDOESQLSERVER;Database=Northwind;Trusted_Connection=True;");
Source: Connection Strings Reference

why would console.writeline show anything. you are not working on console.
in case just to see your output. use Response.writeline(rdr[0]);

Where/how do I write T-SQL in my C# code and get the result (Visual Studio 2008)

I am trying to write t-sql in C# (visual studio). I have this code to connect to the database:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using Microsoft.SqlServer.Server;
namespace WindowsFormsApplication8
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
string connetionString = null;
SqlConnection cnn;
connetionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=C:\\Users\\Xtreme\\Desktop\\CardsDB.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";
cnn = new SqlConnection(connetionString);
try
{
cnn.Open();
MessageBox.Show("Connection Open ! ");
cnn.Close();
}
catch (Exception ex)
{
MessageBox.Show("Can not open connection ! ");
}
}
}
}
Where/how do I write the T-SQL code and how do I get the result?
Can someone give me an simple select example in my code?

You can use DataAdapter.Fill Method:
try
{
using (SqlDataAdapter a = new SqlDataAdapter("SELECT * FROM Employee", cnn))
{
// Use DataAdapter to fill DataTable
DataTable t = new DataTable();
a.Fill(t);
// Render data onto the screen
dataGridView1.DataSource = t; //if you want.
}
}
catch (Exception ex)
{
MessageBox.Show("Problem!");
}

Create a SqlCommand and set the CommandType to CommandType.Text. Then add your SQL to the CommandText property of the SqlCommand.
SqlCommand command = new SqlCommand(commandName, (SqlConnection)Connection);
command.CommandType = CommandType.Text;
command.CommandText = "SELECT * FROM MyTable";
IDataReader result = command.ExecuteReader();

Ardman already showed you how to execute any arbitary sql command. But what i didn't answer very well, is where to put your sql statement.
I think it is a very bad behaviour and also not very good to read if you put your statement directly into the code.
A better method (in my eyes) is the following:
Within your project create a new folder (maybe called Queries)
Right click this folder and select Add - New Item
In the dialog just select Textfile and give it the name about what this query will do
Make sure you replace the file extension from .txt to .sql
Just put your statement right into this file
In the Resource Editor add this file as a resource
Now you can access this sql statement within your project just by using Properties.Resources.MySqlStatement