I can't connect to SQL Server in C#

Question

class ContactsRepository : IContactsRepository
{
    private string connectionString = "Data Source=(LocalDB);Initial Catalog=Contact_DB;User ID=****;Password=**********";

    public bool Delete(int ContactID)
    {
        throw new NotImplementedException();
    }

    public DataTable SelectAll()
    {
        string query = "Select * From MyContacts";
        SqlConnection connection = new SqlConnection(connectionString);
        Sql command = new SqlCommand(query, connection);
        DataTable data = new DataTable();
        adapter.Fill(data);
        return data;
    }
}

I get this error:

System.Data.SqlClient.SqlException: 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: 51 - An instance name was not specified while connecting to a Local Database Runtime. Specify an instance name in the format (localdb)\instance_name.

Just `(localdb)` isn't a valid server+instance name - see the linked connectionstrings.com site for details - it needs to be something like `(localdb)\v11.0`. You can also create your own named instances in "local db" which you then need to specify in the connection string — marc_s, Oct 10 '21 at 09:53
Instead of "(LocalDB)" in your connection string, use "(LocalDB)/something", where that "something" depends on your particular installation. It *is* running on your local computer, isn't it? — Hans Keﬆing, Oct 10 '21 at 10:55
Side note: you really need `using` blocks on your connection and adapter objects — Charlieface, Oct 10 '21 at 11:06

Kamran Mammadov · Answer 1 · 2021-10-10T10:06:38.803

2

https://www.connectionstrings.com/sql-server-2017/

Check here for correct connection string

and also you need "connection.Open()" before run command

public class PullDataTest
{
    // your data table
    private DataTable dataTable = new DataTable();

    public PullDataTest()
    {
    }

    // your method to pull data from database to datatable   
    public void PullData()
    {
        string connString = @"your connection string here";
        string query = "select * from table";

        SqlConnection conn = new SqlConnection(connString);        
        SqlCommand cmd = new SqlCommand(query, conn);
        conn.Open();

        // create data adapter
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        // this will query your database and return the result to your datatable
        da.Fill(dataTable);
        conn.Close();
        da.Dispose();
    }
}

edited Oct 10 '21 at 10:06

answered Oct 10 '21 at 09:36

Kamran Mammadov

103
6

But Visual Studio gives me error line 15 ***adapter.Fill(data);*** – Arsha Heidarzadeh Oct 10 '21 at 09:48
you need open connection thats why – Kamran Mammadov Oct 10 '21 at 09:50
@arhzw because Fill method does everything for you, like open the connection, run the query and then close the connection – Vivek Nuna Oct 10 '21 at 09:50
@KamranMammadov there’s no need to open the connection explicitly with DataAdapter – Vivek Nuna Oct 10 '21 at 09:51
Can you tell me how to write the code? – Arsha Heidarzadeh Oct 10 '21 at 09:55
@arhzw i edited answer check there – Kamran Mammadov Oct 10 '21 at 10:07
I did all the things you said, but visual studio give me an error – Arsha Heidarzadeh Oct 10 '21 at 10:39

I can't connect to SQL Server in C#

1 Answers1