Entity Framework 6 set connection string in code

Question

I have a dll that uses the Entity Framework 6 to do some database operations. I'm using a database first approach. The model and everything concerning the Entity Framework, like the connection string in the App.config, were created via the wizzard in Visual Studio.

So I compiled the dll and put it together with the corresponding .config in the folder where the application using the dll expects it.

Everything works fine until I get to the point where an actual database call is made. There I get the error:

Cannot find connection string for MyDatabaseEntity

The automatically generated connectionstring is, as I said, in the config file of the dll. I cannot change the App.config of the application. But the application hands over an object that has all the information I need to build the connection string myself. So I'm looking for a way to set the connection string in the code without relying on a config file. All the tutorials I find for a database first approach use this method though. I found a post here that says to simply give the connection string as a parameter when creating the Object like

MyDatabaseEntities = new MyDatabaseEntities(dbConnect);

but ´MyDatabaseEntities´ doesn't have a constructor that takes any parameters

public partial class MyDatabaseEntities : DbContext
{
    public MyDatabaseEntities()
        : base("name=MyDatabaseEntities")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

    public virtual DbSet<MyTable> MyTable { get; set; }
}

Answer 1

How about:

public partial class MyDatabaseEntities : DbContext
{
public MyDatabaseEntities(string connectionString)
    : base(connectionString)
{
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    throw new UnintentionalCodeFirstException();
}

public virtual DbSet<MyTable> MyTable { get; set; }

}

Then initialize your database like you did before:

string myConnectionString = "...";
MyDatabaseEntities = new MyDatabaseEntities(myConnectionString);

Answer 2

I had the similar issue. My Edmx and App.Config was in a different project. My startup project was different, had 3 different connection strings, we need to choose one on the fly depending on the environment. So couldn't use a fixed connection string. I created a partial class overload of the Context.cs using the same namespace. Following was my default Context.cs;

namespace CW.Repository.DBModel
{

  public partial class CWEntities : DbContext
  {
      public CWEntities()
        : base("name=CWEntities")
      {
      }

      protected override void OnModelCreating(DbModelBuilder modelBuilder)
      {
        throw new UnintentionalCodeFirstException();
      }
  ...
  ...
  }
}

My partial class overload;

namespace CW.Repository.DBModel
{
    public partial class CWEntities : DbContext
    {
        public CWEntities(string ConnectionString)
            : base(ConnectionString)
        {
        }        
    }
}

Lastly, as my connection strings were not for EF, I converted them to a EF connection string.

public static string GetEntityConnectionString(string connectionString)
    {
        var entityBuilder = new EntityConnectionStringBuilder();

        // WARNING
        // Check app config and set the appropriate DBModel
        entityBuilder.Provider = "System.Data.SqlClient";
        entityBuilder.ProviderConnectionString = connectionString + ";MultipleActiveResultSets=True;App=EntityFramework;";
        entityBuilder.Metadata = @"res://*/DBModel.CWDB.csdl|res://*/DBModel.CWDB.ssdl|res://*/DBModel.CWDB.msl";

        return entityBuilder.ToString();
    }

Lastly, the calling

var Entity = new CWEntities(CWUtilities.GetEntityConnectionString(ConnectionString));