Passing connection strings between assemblies

Question

I have two executables that access a DLL containing Data Access Layer objects Each exe can have a different config containing info on server and database name, connection string etc.

How do I pass the config info to the DAL objects?

Obviously I can pass the config strings to the DAL objects every time I instanciate one, but that seems messy and repetitive as every class in the DAL will require Properties for the Config strings..

Can anyone tell me if there is a better way?

I am wondering if there is a way for the instanciated DAL objects to read some properties from the calling object without me having to pass them explicitly?

Answer 1

What about having all DAL classes derive from a base class which contains the connection string property?

In that case, you could call the base's constructor on the child contructor invocation and that base contructor would then be the single place for loading the Connection string.

If you have the same ConfigKey used in both Exe's eg: "DBConnectionString" - then the contructor will just load the values from config files "DBConnection" entry - no matter which exe is calling the dal and the correct value of connection string will be passed to it

Implementation would be something on below lines... Sorry for using C# - like syntax. i last used VB very many years ago.

class BaseDAL
{
  protected String _connectionString;
  BaseDAL ()
  {
    _connectionString = ConfigurationManager.AppSettings("DBConnectionString") 
  }
  ....    
}

class ChildDAL : BaseDal
{
  ChildDAL():base()
  {
  ....
  }
}

Answer 2

Maybe I am missing something but you can just put the connection string into App.config or Web.config.

<appSettings>
    <!-- This sets the server, the username, and the password to connect to the database -->
    <add key="SqlConnectionString"
             value="Data Source=servername;Database=dbname;User ID=username;Password=password;Charset=utf8;"
    />
</appSettings>

Then, in your code you simply read it in:

Shared connectionString As String = ConfigurationManager.AppSettings("SqlConnectionString")

You only have one App.config per EXE I would think.

If you are truly having a different connection string for each instance of an EXE running you could store it in cache instead but I do not imagine that this is what you are doing.

EDIT: The connection string I use in my example would connect to MySQL. Obviously the connection string itself will vary from database to database.