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Making SQL queries with C# in ASP.NET

I wanted to make a controller in an ASP.NET project that executes a query to a local db (I am using SQL Server From Visual Studio).
The code is the following:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Data.SqlClient;
public class EsempiController : ApiController
{
[Route ("api/Esempi/Ruoli")]
[HttpGet]
public void GetRuoli()
{
string connectionString = #"Data Source=(LocalDB)\MSSQLLocalDB;Integrated Security=True;AttachDbFilename=C:\Users\Pippo\AppData\Local\Microsoft\Microsoft SQLServer Local DB\Instances\MSSQLLocalDB\TestDB.mdf;Connect Timeout=30;TrustServerCertificate = False";
string query = "SELECT Ruoli FROM [dbo].Ruoli ";
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(query, connection);
connection.Open();
}
}
}
When I try to execute the code and searching on: localhost:44363/api/Esempi/Ruoli I get the following error:
System.Data.SqlClient.SqlException: 'An attempt to attach an auto-named database for file C:\Users\Pippo\AppData\Local\Microsoft\Microsoft SQLServer Local DB\Instances\MSSQLLocalDB\TestDB.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.'
This error is showed when the line connection.Open() is executed.
I have already seen other similar problems here but I can't figure it out...
Thanks for the help
PS: I'm using VS 2019 if this can help to undestand.

You can use this site to help you configure you connection string.
An connection string example I am using to do the same thing is:
"Server= localhost; Database= [TABLE_NAME]; Integrated Security=True;"

Unable to make SQL Client Connection tp SQL Server

I'm using Xamarin to connect to SQL Server while making a mobile application. The application runs on iOS. I am using sql client to establish a connection with the server, but I'm running into weird errors and have exhausted most of my options.
Please do not warn me about security issues of direct connections. This is not the concern.
The error I'm receiving is this: provider: tcp provider, error: 40 - could not open a connection to sql server)
Here is my code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using System.Data;
using System.Data.SqlClient;
namespace EmployeeSnapshot
{
// Learn more about making custom code visible in the Xamarin.Forms previewer
// by visiting https://aka.ms/xamarinforms-previewer
[DesignTimeVisible(false)]
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
}
void Button_Clicked(System.Object sender, System.EventArgs e)
{
var EmployeeID = UserInput.Text;
Console.WriteLine(EmployeeID);
string con = "Data Source ={Server}; Initial Catalog ={database}; Integrated Security = False; User ID ={username}; Password ={password}";
string matchingPerson;
using (SqlConnection connection = new SqlConnection(con))
{
string oString = "SELECT something FROM table WHERE employeeid = #employeeID";
SqlCommand command = new SqlCommand(oString, connection);
command.Parameters.AddWithValue("#employeeID", EmployeeID);
connection.Open();
Console.WriteLine("State: {0}", connection.State);
using (SqlDataReader reader = command.ExecuteReader())
{
matchingPerson = reader["name"].ToString();
}
command.Connection.Close();
}
Console.WriteLine(matchingPerson);
}
}
}
The code errors out at the Connection.open() line.
What I've tried:
changed the connection string around, messed with integrated security, ensured the servers are up and running, etc.
I am making this app on a MacBook. I have parallels, so I can use a virtual machine to go into windows. I decided to take advantage of this, and copied my connection string and pasted it into visual studio on the windows side. I performed a basic select statement and retrieved the data no problem, so the connection string doesn't seem to be the issue.
I almost feel like it has something to do with Xamarin or with the fact I'm on a MacBook.

I was right - the problem was with Xamarin/The visual studio project itself. All I did was clean and rebuild the solution to get everything to work. Xamarin is buggy and when in doubt, from this experience, I have learned to clean and rebuild when libraries aren't acting as expected.

Cannot connect to MySQL database in C#.NET

So I'm following this tutorial: http://support.microsoft.com/kb/314145/
and I get an unexpected error: A first chance exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll
My class looks like this:
class Database
{
public Database()
{
string connectionString = "Password=pass;User ID=userid;Initial Catalog=soksko;Data Source=(local)";
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
Console.WriteLine("ServerVersion: {0}", connection.ServerVersion);
Console.WriteLine("State: {0}", connection.State);
}
Console.WriteLine("Database: OK");
}
}
I googled, but I couldnt find anything valuable. I am using MySQL database, it is on the same computer and I am using VS 2013. I successfully added my database to Server Explorer with the same connection information that I use above, but I get exception, when I try to open the connection.

See this link for how a MySQL connection string should look:
ASP.NET use SqlConnection Connect Mysql
See this link for an explanation of the oft mis-used Data Source=(local):
http://blogs.msdn.com/b/sql_protocols/archive/2008/09/19/understanding-data-source-local-in-sql-server-connection-strings.aspx
hint you're not using SQL-Server so it won't work for you

SqlConnection is for MS SQL Server. For MySql you need to use a MySqlConnection class provided by the MySQL connector (http://dev.mysql.com/doc/connector-net/en/index.html)
using MySql.Data.MySqlClient;
using(MySqlConnection myConnection = new MySqlConnection(myConnectionString))
{
myConnection.Open();
// execute queries, etc
}

The tutorial you're using is for Sql Server, not MySQL.

Connecting C# to SQL Server Compact database

Hi I'm trying to connect an SQL server compact database to my program and I want a button that deletes all entries from the database, when I Press said button the program throws an exception and gives the following error message "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)"
Help Please? =]
Sorry, Code is Below =]
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 System.Data.SqlServerCe;
namespace Booking_system_Final
{
public partial class PendingJobs : Form
{
SqlConnection sc = new SqlConnection("Data Source=C:\\Users\\Administrator\\My Documents\\BMS_Data.sdf");
public PendingJobs()
{
InitializeComponent();
}
private void PendingJobs_Load(object sender, EventArgs e)
{
// TODO: This line of code loads data into the 'bMSDataSet.Bookings' table. You can move, or remove it, as needed.
this.bookingsTableAdapter.Fill(this.bMSDataSet.Bookings);
// TODO: This line of code loads data into the 'bMS_DataDataSet1.Bookings' table. You can move, or remove it, as needed.
}
private void button1_Click(object sender, EventArgs e)
{
sc.Open();
SqlCommand cmd = new SqlCommand("DELETE FROM Bookings");
cmd.Connection = sc;
cmd.ExecuteNonQuery();
sc.Close();
MessageBox.Show("Database Cleared");
}
}
}

Try use SqlCeConnection class rather than SqlConnection:
SqlCeConnection sqlConnection1 = new SqlCeConnection();
sqlConnection1.ConnectionString = "Data Source = C:\\Users\\Administrator\\My Documents\\BMS_Data.sdf;Persist Security Info=False";

If you want to connect to SQL Server Compact, use SqlCeConnection, SqlCeCommand etc. Add a reference to the SQL Server Compact ADO.NET provider, System.Data.SqlServerCe.dll

Have a look at this blog article: SQL SERVER – FIX : ERROR : (provider: Named Pipes Provider, error: 40 – Could not open a connection to SQL Server)
This goes step-by-step through what you might need to do:
In short:
SQL Server should be up and running.
Enable TCP/IP in SQL Server Configuration
Open Port in Windows Firewall
Enable Remote Connection
Enable SQL Server Browser Service
Create exception of sqlbrowser.exe in Firewall
Recreate Alias
About the where and what to do in each step, you will find more in-depth information in the article.
You may also want to have a look at the Connection strings for SQL Server Compact. There you can find other variations of the connection string you could try to play with.

You seems to be using a bad connection string. (Or the file path is wrong). Check out http://www.connectionstrings.com/sql-server-ce for connection string options.

Connection to sql server express with visual studio 2010

I'm new to .net and c# and want to connect Sql server express available in visual studio 2010.
I have searched a lot and read connection strings in connectionstrings.com but still don't know how to connect.
i added a "service-based database" with adding new item and now have a db.mdf with tables.
my code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
namespace ConsoleApplication1
{
class First
{
static void Main()
{
SqlConnection con = new SqlConnection("Data Source=(local);Initial Catalog=db2.mdf;Integrated Security=True");
con.Open();
Console.WriteLine("ok");
Console.ReadLine();
}
}
}
but it does not connect. in fact it executes with no errors , but no output for Console.WriteLine("ok");
how should be the connection-string in my case? specially for "Data source". I don't know what should its value be. please tell me the full connection-string which suits my case.
I'm really new to .net and confused many days for a simple connection.
also tried many other connection strings , but not working...

try with this code
using(var connection = new SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\db2.mdf;Integrated Security=True;User Instance=True")
{
}