how do I use a connecting string variable defined in a file reuse in another file in same C# project?

Question

I've a databaseconnectionString variable in file databasetablename.cs and I want to use this databaseconnectionString in my other files without creating the connection string details for each api,following is how my project structure looks like and how I tried to use the variable databaseconnectionString which throws an error doesnot exist in current context ,what am I missing?how to use the databaseconnectionString in product.cs file?

Repository
   --->BuildRepositoryfolder
       Product.cs
   --->DatabaseConnections
       databasetablename.cs


databasetablename.cs

    public class databasetablename
    {
        public string databaseconnectionString = "server=xx.xx.xxx.xxx;database=aci_dev;uid=wciadmin;pwd=adSHEEP91min;";
    }

Product.cs
      public IEnumerable<Info> InfoSearch(LookaheadRunsFilterCriteria filterCriteria)
       {  
            var conn = new MySql.Data.MySqlClient.MySqlConnection();
            conn.ConnectionString = databaseconnectionString; --> throws an error

       }

Answer 1

In C#, to use a variable defined in one class from another there are several requirements. If DatabaseTable is a class with a variable ConnectionString that you want to use inside another class Program , then:

1. The two classes must be in the same assembly/project and ConnectionString must be marked public or internal -- OR -- ConnectionString must be marked public and DatabaseTable must be marked public and the project with Program must reference the project with DatabaseTable .

In one project:

class Program {
    public static void Main() {
        var str = DatabaseTable.ConnectionString;
    }
}

class DatabaseTable {
    internal static string ConnectionString = "test";
}

In separate projects:

class Program {
    public static void Main() {
        var str = DatabaseTable.ConnectionString;
    }
}

public class DatabaseTable {
    public static string ConnectionString = "test";
}

Access modifiers (MSDN)

---

2. If you want ConnectionString to be available to Program by just referencing the DatabaseTable class, without creating an instance of that class, then ConnectionString must be marked static or const .

With instances:

class Program {
    public static void Main() {
        var table = new DatabaseTable();
        var str = table.ConnectionString;
    }
}

public class DatabaseTable {
    public string ConnectionString = "test";
}

With static :

class Program {
    public static void Main() {
        var str = DatabaseTable.ConnectionString;
    }
}

public class DatabaseTable {
    public static string ConnectionString = "test";
}

const (MSDN)

static (MSDN)

Answer 2

我想这就是你想要的：

conn.ConnectionString = databasetable.databaseconnectionString;

Answer 3

You may also try singleton pattern. I will give You example I have in my project already. I am using OleDbConnection , but You may adjust it for Your purpose ( MySqlConnection ). You will have to connect only once. Your methods related to database could be also inside Broker.cs . Later, for example inside form, when needed, You will be using Broker.dajBrokera().methodName() . You will have to add using namespace (name) too. Note private constructor, and dajBrokera() which will create only one instance of Broker class.

public class Broker
{
  OleDbConnection konekcija;

  OleDbCommand komanda;

  void konektujSe()
  {
        konekcija = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\...;Persist Security Info=False;");
        komanda = konekcija.CreateCommand();
  }

  private static Broker broker;

  public static Broker dajBrokera()
  {
      if (broker == null)
      {
          broker = new Broker();
      }
      return broker;
  }

  private Broker()
  {
      konektujSe();
  }
}

Hope this can help. Sorry for using OleDbConnection, instead MySqlConnection.It would take me more time to answer, and I suppose faster answer could be more helpful. Best regards.