Test

example.rb

def initialize(opts = {})
      @db_type = if !opts || opts.empty?
                   'sqlite'
                 else
                   opts['database']['type']
                 end
      set_database
    end

    def self.from_config_file
      @@db_path = File.join(Dir.pwd, '/config/database/database_config.yml')
      db_opts = YAML.load_file(@@db_path)
      SSHScan::DatabaseConfig.new(db_opts)
    end

    def set_database
      if @db_type.eql? 'mongodb'
        return SSHScan::Database::MongoDb.from_config_file(@@db_path)
      elsif @db_type.eql? 'sqlite'
        return SSHScan::Database::SQLite.from_config_file(@@db_path)
      end
    end

# Set this in api.rb

set :db, SSHScan::DatabaseConfig.from_config_file

# It shows error:
# NoMethodError - undefined method `add_scan' for #<SSHScan::DatabaseConfig:0x000000022638b8 @db_type="sqlite">

Although I was able to use @db_type instance var. But, it returns SSHScan::DatabaseConfig class.