Develop Reference

Access SQL server using C# with generic credentials

I have a generic user (username:user and password:user) that has access to my SQL Database.
So, if I use the following code, I can access to it without problems:
using System.Data.SqlClient;
namespace ConsoleApp1
{
Class Program
{
static void Main(string[] args)
{
string conString = "Data source=server; Initial catalog=db; Integrated security=true";
SqlConnection conn = new SqlConnection(conString);
using (conn)
{
conn.Open();
SqlCommand command = new SqlCommand("SELECT * FROM Table", conn);
SqlDataReader reader = command.ExecuteReader();
conn.Close();
}
}
}
}
However, if I change the conString by replacing IntegratedSecurity=true by User ID=user; Password=user, then I have the exception
System.Data.SqlClient.SqlException:'Login failed for user 'user'.'
I would like to hardcode those credentials so every user without access to the database may use those generic credentials, but I cannot solve that exception.

ExecuteNonQuery: Connection property has not been initialized using visual studio 15

I caņ't seem to get around this error message: ExecuteNonQuery: Connection property has not been initialized
It refers to a cmd.ExecuteNonQuery();
I'm not really sure what is going on, maybe the insert is not correct, but here is my code:
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 System.Data.SqlClient;
namespace md2
{
public partial class Form2 : Form
{
SqlConnection cn = new SqlConnection(#"Data Source=.\SQLEXPRESS;Initial Catalog=MD2;Integrated Security=True;Pooling=False");
SqlCommand cmd = new SqlCommand();
SqlDataReader dr;
public Form2()
{
InitializeComponent();
}
private void label2_Click(object sender, EventArgs e)
{
cmd.Connection = cn;
}
private void button2_Click(object sender, EventArgs e)
{
if (izd_adr.Text != "" && izd_nos.Text != "") {
cn.Open();
cmd.CommandText = "insert into Publisher (pu_id, pub_name, adress) values ("+null+"'Elina', 'Kalnina')";
cmd.ExecuteNonQuery();
cmd.Clone();
MessageBox.Show("Ir pievienots");
cn.Close();
new Form1().Show();
}
}
}
}
I followed a tutorial in how to do this, but I'm getting this error.
That Database looks like this:
This seems like a easy mistake somewhere, but is really frustrating...

You need to set the connection property on the command object:
cmd.Connection = cn;
An easier way to manage this is to let the SqlConnection create the command, which associates the SqlCommand with the SqlConnection: ie
cmd = cn.CreateCommand();

move cmd.Connection = cn; into the button click event. When you click the button currently, cmd has no connection property.

You must pass the SqlConnection to the SqlCommand, either with SqlCommand.Connection, pass it in the constructor or use CreateCommand().
I recommend creating a new SqlCommand and SqlConnection object when needed and refrain from caching them. SQL server does connection pooling anyway:
using (SqlConnection connection = new SqlConnection(...))
{
connection.Open();
using (SqlCommand cmd = new SqlCommand("....", connection))
{
}
}

Change the Connection String as given below If you are using Compact 4.0 Database
SqlConnection cn = new SqlConnection(#"Data Source=|DataDirectory|\MD2.sdf");
SqlCommand cmd = new SqlCommand();
SqlDataReader dr;
you can change the Provider Name according to you SQL Server Name.
and Move cmd.Connection = cn; into the button2_click event.

I agree with S. Laurijssen, and would like to emphasize that his example uses using blocks. Because SqlConnection and SqlCommand both implement IDisposable, each is automatically closed properly at the end of the block. My example put this in a class called Common.
My only, additional suggestion would be that you create a public static method that generates a SqlConnection object, opens it, and then returns the instantiated, opened connection. You can then do something like this:
using (SqlConnection cn = Common.GetConnection())
{
using (SqlCommand cmd = new SqlCommand("[your SQL command here]", cn))
{
}
}
With this pattern, you do not need to remember to open or close your SqlConnection, and your code is cleaner.

Execute any Raw SQL Query

IS it possible to execute a raw SQL command of any type (SELECT, UPDATE, DELETE....) in C#. I am looking to add a feature similar to the SQL Server Management Studio query window where I can just type in any SQL command and it executes it. In my case I am not worried about sql injection, I know this risk with this feature. All the connection parameters are passed to me (I have a valid connection string), but I know nothing about the database itself. The SQL command is also syntactically correct before I get the command. I cannot seem to find a solution that will work in all cases, probably just overlooking the obvious solution.

Here is an ADO example for you
using System;
using System.Data;
using System.Data.SqlClient;
class Program
{
static void Main()
{
string connectionString =
"Data Source=(local);Initial Catalog=Northwind;"
+ "Integrated Security=true";
// Provide the query string with a parameter placeholder.
string queryString =
"UPDATE [dbo].[USR_Users] SET [Active] = 1 WHERE Id = 1";
using (SqlConnection connection =
new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(queryString, connection);
try
{
connection.Open();
command.ExecuteNonQuery();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.ReadLine();
}
}

You can simply use ADO .NET and show the results of the query if it executed successfully or not, just put the following code in the event handler when you want to execute your query:
using (SqlConnection conn = ConnectionClass.GetInstance().Connection())
using (SqlCommand cmd = new SqlCommand(TextBoxQuery.Text, conn))
{
conn.Open();
TextBoxNoOfRowEffected.Text = cmd.ExecuteNonQuery().ToString();
}
SqlCommand.ExecuteNonQuery() Documentation

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