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Connection to database

I am trying to create a class that I can use within my application to easily connect to my database and run queries as needed. I found this post but it is not quite working like I expect.
Here is my class:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
//a class that returns a connection to the database
namespace epaCUBE_Utility_Tool
{
public class epaCUBE_DB
{
public static SqlConnection GetConnection()
{
string str = "user id=MyUserName;" +
"password=MyPassword;server=myServer;" +
"database=myDatabase; " +
"connection timeout=30";
SqlConnection con = new SqlConnection(str);
con.Open();
return con;
}
}
}
and here is how I am trying to use it:
private void button1_Click(object sender, EventArgs e)
{
var connection = epaCUBE_DB.GetConnection();
connection.Open();
SqlDataReader rdr = null;
string CommandText = "SELECT Field1, Field2 FROM TableName";
SqlCommand cmd = new SqlCommand(CommandText, connection);
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
this.comboBox1.Items.Add(rdr["Field1"].ToString() +
": " + rdr["Field2"].ToString());
}
connection.Close();
}
when I press the button I get an error
InvalidOperationException: The connection was not closed. The connection's current state is open.
What am I doing wrong?
Thanks,
Leslie

GetConnection calls Open for you, but you're calling it again manually after you called GetConnection. Call it inside GetConnection or outside, but not both places.

Problem is in GetConnection() you already open the connection. All these problems came with your static method.
This is not good way to do this, better to create a new instance of SqlConnection when you need and dispose after use. The underlying connection pooling will be able to manage the physical connections.
separate your UI with Data access, Here you read the data from database and same time adding items to controls. You need to re-factor the code.
You can have method like below to retrieve data
public List<string> GetFields()
{
List<string> fields = new List<string>();
string CommandText = "SELECT Field1, Field2 FROM TableName";
using (var connection = new SqlConnection(epaCUBE_DB.GetConnectionString()))
{
connection.Open();
using (var cmd = new SqlCommand(CommandText, connection))
using (var reader = cmd.ExecuteReader())
{
while (reader.Read())
{
fields.Add(reader["Field1"].ToString() + ": " + reader["Field2"].ToString());
}
}
}
return fields;
}

You're trying to open a connection which is already open, this results in exception.
before opening the connection check the connection status and then open the connection
cmd.Connection.Open();
add the following check/cleanup code:
if (cmd.Connection.State == ConnectionState.Open)
{
cmd.Connection.Close();
}

I program quite defensively; I expect faults to occur and try to handle that gracefully.
As such..
// Define this once in a class and re-use for every connection..
string myConnString = "user id=MyUserName;" +
"password=MyPassword;server=myServer;" +
"database=myDatabase; " +
"connection timeout=30";
using (SqlConnection mySqlConnection = new SqlConnection(myConnString))
{
using (SqlCommand mySQLCommand = new SqlCommand("SELECT Field1, Field2 FROM TableName", mySqlConnection) { CommandType = CommandType.Text})
{
try
{
mySqlConnection.Open();
using (SqlDataReader rdr = mySQLCommand.ExecuteReader())
{
this.comboBox1.Items.Add(rdr["Field1"].ToString() + ": " + rdr["Field2"].ToString());
}
}
catch (Excecption e)
{
// Deal with it as you wish
}
mySqlConnection.Close();
}
}

reading one record from access in C#

My requirement is to read Date column from access file and use one value to append it to a file name, so as to create file with date timestamp using the db value.
I am trying following approach but it gives me exception "No data exists for the row/column":
here's the code
OleDbConnection conn = new OleDbConnection(connectionString);
OleDbConnection conn1 = new OleDbConnection(connectionString);
string dt = "SELECT top 1 Date FROM Events";
OleDbCommand cmd1 = new OleDbCommand(dt, conn1);
conn1.Open();
OleDbDataReader rdr = cmd1.ExecuteReader();
string time_stmp = rdr.GetInt32(0).ToString();
rdr.Close();
conn1.Close();
string path = text_dir + "\\" + time_stmp + "_" + "BWC_Ejournal.txt";

You'll need to call the Read() method on the OleDbDataReader object before accessing its data.
E.g.
OleDbDataReader rdr = cmd1.ExecuteReader();
string time_stmp = "";
if(rdr.Read())
{
time_stmp = rdr.GetInt32(0).ToString();
}
else
{
//handle no data situation here
}
This will also allow to handle a situation where no data is returned more gracefully too.

DATE is a reserved word in ACE/Jet SQL. Try this instead:
string dt = "SELECT TOP 1 [Date] FROM Events";
Edit
On taking a closer look at your code I notice that you create the OleDbCommand object before the connection is opened. I've seen that cause problems as well. FWIW, the following code works for me:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.OleDb;
namespace oleDbTest
{
class Program
{
static void Main(string[] args)
{
using (var con = new OleDbConnection(
"Provider=Microsoft.ACE.OLEDB.12.0;" +
#"Data Source=C:\__tmp\main.accdb;"))
{
con.Open();
using (var cmd = new OleDbCommand(
"SELECT TOP 1 [Date] FROM [Events]", con))
{
string time_stmp = Convert.ToDateTime(cmd.ExecuteScalar()).ToString("yyyyMMdd");
Console.WriteLine(time_stmp.ToString());
}
con.Close();
}
Console.WriteLine("Done.");
System.Threading.Thread.Sleep(2000);
}
}
}

Info repeatedly getting recorded in DB

I have a Form where I am inserting a record into the database. There are two tables, table_1 is called members, and table_2 is called Amount.
I am using two SQL INSERT statements to send records to database , because that’s the way I have figured out -- there might be other ways, which I don’t know.
When I insert the record I get a message that it is inserted successfully, but when I check the database the inserted record replaces the one present , so I have last record in the DB repeated several times. Please assist.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace CemiyetAidatSistem
{
public partial class AddMember : Form
{
public AddMember()
{
InitializeComponent();
}
SqlConnection con = new SqlConnection("Data Source=My-PC\\SQLSERVER;Initial Catalog=FredericiaDernek;Integrated Security=True");
private void btnInsert_Click(object sender, EventArgs e)
{
SqlCommand cmd = new SqlCommand();
string Sql = "INSERT INTO Uyeleri ( dID, FullName, Address, Mobile, Email, Comments ) VALUES ('" + txtdID.Text + "', '" + txtAdiSoyadi.Text + "','" + txtAddress.Text + "','" + txtMobile.Text + "','" + txtEmail.Text + "','" + txtComments.Text + "')";
cmd.CommandText = Sql;
cmd.Connection = con;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
Sql = "INSERT INTO Aidat (dID Year, Amount ) VALUES ('"+ txtdID.Text +"','" + txtYear.Text + "','" + txtAmount.Text + "')";
cmd.CommandText = Sql;
cmd.Connection = con;
con.Open();
cmd.ExecuteNonQuery();
con.Close();
for (int i = 0; i < this.Controls.Count; i++)
{
if (this.Controls[i] is TextBox)
{
this.Controls[i].Text = "";
}
}
MessageBox.Show("Data Added Scuessfully");
}
}
}

I have rewritten your code to correct errors and bad practices
string connString = "Data Source=My-PC\\SQLSERVER;Initial Catalog=FredericiaDernek;Integrated Security=True";
private void btnInsert_Click(object sender, EventArgs e)
{
using(SqlConnection con = new SqlConnection(connString))
{
con.Open();
string Sql = "INSERT INTO Uyeleri (dID, FullName, Address, Mobile, Email, Comments ) " +
"VALUES (#id, #name, #address, #mobile, #email, #comments");
using(SqlCommand cmd = new SqlCommand(Sql, con))
{
cmd.Parameters.AddWithValue("#id", txtdID.Text);
cmd.Parameters.AddWithValue("#name", txtAdiSoyadi.Text);
cmd.Parameters.AddWithValue("#address", txtAddress.Text);
cmd.Parameters.AddWithValue("#mobile", txtMobile.Text);
cmd.Parameters.AddWithValue("#email", txtEmail.Text);
cmd.Parameters.AddWithValue("#comments", txtComments.Text);
cmd.ExecuteNonQuery();
Sql = "INSERT INTO Aidat (dID, [Year], Amount ) VALUES " +
"(#id, #year, #amount)";
cmd.Parameters.Clear();
cmd.CommandText = Sql; // <- missing this in the previous version.....
cmd.Parameters.AddWithValue("#id", txtdID.Text);
cmd.Parameters.AddWithValue("#name", txtYear.Text);
cmd.Parameters.AddWithValue("#amount", txtAmount.Text);
cmd.ExecuteNonQuery();
}
}
What I have changed:
The second insert statement is wrong. Missing a comma between first
and second column
Removed the creation of the SqlConnection at the global level
Added appropriate using statement to dispose the SqlConnection and
SqlCommand also in case of exceptions
Used parameters for the two insert statements
Added square brackets around Year field (Year is a reserved keyword
in T-SQL)
Creating a SqlConnection at the global level is bad, because you grab system resources and you don't dispose them for the lifetime of your application. And the situation could be out of control in case of exceptions not correctly handled.
Now I have some doubt about your tables. The fields dID (both tables) and Amount are of text type (varchar,nvarchar)?. If they are of numeric type it is necessary to add a conversion before adding the values to the Parameters collection

I would also suggest changing your for loop to clear the controls replace this
for (int i = 0; i < this.Controls.Count; i++)
{
if (this.Controls[i] is TextBox)
{
this.Controls[i].Text = "";
}
}
with the following code using linq.
this.Controls.OfType<TextBox>().ToList().ForEach(textBox => textBox.Clear());
keep in mind that 'this' will refer to the name of your Form
so it would be
(YourWinFormsName).Controls.OfType<TextBox>().ToList().ForEach(textBox => textBox.Clear());

display information from sql db to asp.net webpage

I think what I need is simple but I can't achieve it through asp.net because I am a total beginner.
What I need is to display a field from sql db table to my webpage like this example:
Account Information
Your Name is: <Retrieve it from db>
Your Email is: <Retrieve it from db>
How should I do that ?
I already have table members.
I need to do this with c# , I am using Visual Studio Web Express 2010

First step is add the SQL Client namespace:
using System.Data.SqlClient;
DB Connection
Then we create a SqlConnection and specifying the connection string.
SqlConnection myConnection = new SqlConnection("user id=username;" +
"password=password;server=serverurl;" +
"Trusted_Connection=yes;" +
"database=database; " +
"connection timeout=30");
This is the last part of getting connected and is simply executed by the following (remember to make sure your connection has a connection string first):
try
{
myConnection.Open();
}
catch(Exception e)
{
Console.WriteLine(e.ToString());
}
SqlCommand
An SqlCommand needs at least two things to operate. A command string, and a connection. There are two ways to specify the connection, both are illustrated below:
SqlCommand myCommand = new SqlCommand("Command String", myConnection);
// - or -
myCommand.Connection = myConnection;
The connection string can also be specified both ways using the SqlCommand.CommandText property. Now lets look at our first SqlCommand. To keep it simple it will be a simple INSERT command.
SqlCommand myCommand= new SqlCommand("INSERT INTO table (Column1, Column2) " +
"Values ('string', 1)", myConnection);
// - or -
myCommand.CommandText = "INSERT INTO table (Column1, Column2) " +
"Values ('string', 1)";
SqlDataReader
Not only do you need a data reader but you need a SqlCommand. The following code demonstrates how to set up and execute a simple reader:
try
{
SqlDataReader myReader = null;
SqlCommand myCommand = new SqlCommand("select * from table",
myConnection);
myReader = myCommand.ExecuteReader();
while(myReader.Read())
{
Console.WriteLine(myReader["Column1"].ToString());
Console.WriteLine(myReader["Column2"].ToString());
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}

How do I connect to a database and loop over a recordset in C#?

What's the simplest way to connect and query a database for a set of records in C#?

#Goyuix -- that's excellent for something written from memory.
tested it here -- found the connection wasn't opened. Otherwise very nice.
using System.Data.OleDb;
...
using (OleDbConnection conn = new OleDbConnection())
{
conn.ConnectionString = "Provider=sqloledb;Data Source=yourServername\\yourInstance;Initial Catalog=databaseName;Integrated Security=SSPI;";
using (OleDbCommand cmd = new OleDbCommand())
{
conn.Open();
cmd.Connection = conn;
cmd.CommandText = "Select * from yourTable";
using (OleDbDataReader dr = cmd.ExecuteReader())
{
while (dr.Read())
{
Console.WriteLine(dr["columnName"]);
}
}
}
}

Very roughly and from memory since I don't have code on this laptop:
using (OleDBConnection conn = new OleDbConnection())
{
conn.ConnectionString = "Whatever connection string";
using (OleDbCommand cmd = new OleDbCommand())
{
cmd.Connection = conn;
cmd.CommandText = "Select * from CoolTable";
using (OleDbDataReader dr = cmd.ExecuteReader())
{
while (dr.Read())
{
// do something like Console.WriteLine(dr["column name"] as String);
}
}
}
}

That's definitely a good way to do it. But you if you happen to be using a database that supports LINQ to SQL, it can be a lot more fun. It can look something like this:
MyDB db = new MyDB("Data Source=...");
var q = from db.MyTable
select c;
foreach (var c in q)
Console.WriteLine(c.MyField.ToString());

This is an alternative way (DataReader is faster than this one):
string s = "";
SqlConnection conn = new SqlConnection("Server=192.168.1.1;Database=master;Connect Timeout=30;User ID=foobar;Password=raboof;");
SqlDataAdapter da = new SqlDataAdapter("SELECT TOP 5 name, dbid FROM sysdatabases", conn);
DataTable dt = new DataTable();
da.Fill(dt);
for (int i = 0; i < dt.Rows.Count; i++)
{
s += dt.Rows[i]["name"].ToString() + " -- " + dt.Rows[i]["dbid"].ToString() + "\n";
}
MessageBox.Show(s);

If you are intending on reading a large number of columns or records it's also worth caching the ordinals and accessing the strongly-typed methods, e.g.
using (DbDataReader dr = cmd.ExecuteReader()) {
if (dr.Read()) {
int idxColumnName = dr.GetOrdinal("columnName");
int idxSomethingElse = dr.GetOrdinal("somethingElse");
do {
Console.WriteLine(dr.GetString(idxColumnName));
Console.WriteLine(dr.GetInt32(idxSomethingElse));
} while (dr.Read());
}
}

If you are querying a SQL Server database (Version 7 and up) you should replace the OleDb classes with corresponding classes in the System.Data.SqlClient namespace (SqlConnection, SqlCommand and SqlDataReader) as those classes have been optimized to work with SQL Server.
Another thing to note is that you should 'never' select all as this might lead to unexpected results later on if you add or remove columns to this table.

I guess, you can try entity framework.
using (SchoolDBEntities ctx = new SchoolDBEntities())
{
IList<Course> courseList = ctx.GetCoursesByStudentId(1).ToList<Course>();
//do something with courselist here
}

Charge the libraries
using MySql.Data.MySqlClient;
This is the connection:
public static MySqlConnection obtenerconexion()
{
string server = "Server";
string database = "Name_Database";
string Uid = "User";
string pwd = "Password";
MySqlConnection conect = new MySqlConnection("server = " + server + ";" + "database =" + database + ";" + "Uid =" + Uid + ";" + "pwd=" + pwd + ";");
try
{
conect.Open();
return conect;
}
catch (Exception)
{
MessageBox.Show("Error. Ask the administrator", "An error has occurred while trying to connect to the system", MessageBoxButtons.OK, MessageBoxIcon.Error);
return conect;
}
}