namespace MinimalBlog.Dal.SqlServer

public class SqlServerDbContext : MinimalBlogDbContext
{
        //Sql Server Settings
}

namespace MinimalBlog.Dal.Sqlite

public class SqliteDbContext : MinimalBlogDbContext
{
        //Sqlite Settings
}

var connectionStringKey = Configuration.GetConnectionString("InUseKey");
var connectionString = Configuration.GetConnectionString(connectionStringKey);

switch (connectionStringKey)
{
    case "SqlServerConnection":
        services.AddScoped<MinimalBlogDbContext, SqlServerDbContext>();
        services.AddDbContext<SqlServerDbContext>(options => opt.UseSqlServer(connectionString));
        break;
    case "SqliteConnection":
        services.AddScoped<MinimalBlogDbContext, SqliteDbContext>();
        services.AddDbContext<SqliteDbContext>(options => options.UseSqlite(connectionString));
        break;
    default:
        throw new NotImplementedException($"`{connectionStringKey}` is not defined in `appsettings.json` file.");
}

public class Order
{
    public int Id { get; set; }
    public Customer Customer { get; set; }
}
public class Customer
{
    public int Id { get; set; }
}
......

modelBuilder.Entity<Order>().HasRequired(ff => ff.Customer);

public static string CreateConnectionStringForSQLCe(string dbPath = @"|DataDirectory|\NerdDinners.sdf")
{
   SqlCeConnectionStringBuilder sqlConnection = new SqlCeConnectionStringBuilder();
   sqlConnection.Password = "9023fase93";
   sqlConnection.DataSource = dbPath;

   EntityConnectionStringBuilder connection = new EntityConnectionStringBuilder();
   connection.Metadata = @"res://*/NerdDinnersModel.csdl|res://*/NerdDinnersModel.ssdl|res://*/NerdDinnersModel.msl";
   connection.Provider = "System.Data.SqlServerCe.3.5";
   connection.ProviderConnectionString = sqlConnection.ToString();

   return connection.ToString();
}


public static string CreateConnectionStringForSQLServer()
{
   //Build an SQL connection string
   SqlConnectionStringBuilder sqlString = new SqlConnectionStringBuilder()
   {
      DataSource = "MyPC", // Server name
      InitialCatalog = "db1",  //Database
      UserID = "user1",         //Username
      Password = "mypassword",  //Password
   };
 
   //Build an Entity Framework connection string
   EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder
   {
      Provider = "System.Data.SqlClient",
      Metadata =   "res://*/testModel.csdl|res://*/testModel.ssdl|res://*/testModel.msl",
      ProviderConnectionString = sqlString.ToString()
   };
   return entityString.ConnectionString;
}

  context.CommandTimeout = 180;

                catch (Exception ex)
                {
                    StringBuilder errorMsg = new StringBuilder();
                    for (Exception current = ex; current != null; current = current.InnerException)
                    {
                        if (errorMsg.Length > 0)
                            errorMsg.Append("\n");

                        errorMsg.Append(current.Message.Replace("See the inner exception for details.", string.Empty));
                    }
                    // log
                    errorMsg.ToString();
                }

    private static void ListenToLocalChanges()
    {
        using (var context = new BreakAwayContext())
        {
            context.Destinations.Local.CollectionChanged += (sender, args) =>
            {
                if (args.NewItems != null)
                {
                    foreach (Destination item in args.NewItems)
                    {
                        Console.WriteLine("Added: " + item.Name);
                    }
                }
                if (args.OldItems != null)
                {
                    foreach (Destination item in args.OldItems)
                    {
                        Console.WriteLine("Removed: " + item.Name);
                    }
                }
            };
            context.Destinations.Load();
        }
    }