build an database connection with PG

database.yml

development:
  encoding: utf8
  port: 5432
  database: development
  username: username
  password:
  host: localhost
---
test:
  encoding: utf8
  port: 5432
  database: test 
  username: username
  password:
  host: localhost
---

db.cr

require "yaml"

module Importation
  class DB
    include Importation

    property(db, env)

    def initialize(env)
      @env = env
    end

    def connection
      @db ||= PG.connect(conection_string)
    end

    def conection_string
      config = configuration

      base_string = "postgresql://#{config["host"]}:#{config["port"]}/#{config["database"]}?"
      
      # user=#{config["username"]}&password=#{config["password"]}&client_encoding=#{config["encoding"]}"
      
      config_array = config.map do |key, value|
        next if value.nil?
        "#{key}=#{value}"
      end.compact!

      base_string + config_array.join("&")
    end

    def configuration
      base = base_configuration
      config = configuration_by_env
      base.each { |key, value| config[key] = value unless config.keys.includes?(key) }
      config
    end

    def base_configuration
      {
        "encoding" => "utf8",
        "port" => "5432",
        "database" => "default",
        "username" => "root",
        "password" => "",
        "host" => "localhost"
      }
    end

    def configuration_by_env
      data[@env] as Hash
    end

    def data
      YAML.load(File.read("#{root}/config/database.yml")) as Hash
    end
  end
end

error.log

Error in macro 'pp' /usr/local/Cellar/crystal-lang/0.9.0/src/macros.cr:52, line 2:

  1.   
  2.     ::puts "#{ "database.conection_string" } = #{ (database.conection_string).inspect }"
  3.   

    ::puts "#{ "database.conection_string" } = #{ (database.conection_string).inspect }"
                                                            ^~~~~~~~~~~~~~~~

instantiating 'Importation::DB#conection_string()'
in ./app/importation/db.cr:24: instantiating 'Hash(YAML::Type, YAML::Type)#map()'

      config_array = config.map do |key, value|
                            ^~~

in /usr/local/Cellar/crystal-lang/0.9.0/src/hash.cr:444: instantiating 'each()'

    each do |k, v|
    ^~~~

in /usr/local/Cellar/crystal-lang/0.9.0/src/hash.cr:444: instantiating 'each()'

    each do |k, v|
    ^~~~

in /usr/local/Cellar/crystal-lang/0.9.0/src/hash.cr:445: instantiating 'Array(String)#push(String?)'

      array.push yield k, v
            ^~~~

in /usr/local/Cellar/crystal-lang/0.9.0/src/array.cr:1251: instantiating '{String?}#each()'

    values.each do |value|
           ^~~~

in /usr/local/Cellar/crystal-lang/0.9.0/src/array.cr:1251: instantiating '{String?}#each()'

    values.each do |value|
           ^~~~

in /usr/local/Cellar/crystal-lang/0.9.0/src/array.cr:1252: no overload matches 'Array(String)#<<' with types String?
Overloads are:
 - Array(String)#<<(value : String)
Couldn't find overloads for these types:
 - Array(String)#<<(value : Nil)

      self << value
           ^~

================================================================================

Nil trace:

  /usr/local/Cellar/crystal-lang/0.9.0/src/array.cr:1251

        values.each do |value|
                        ^~~~~

  macro macro_4427918288 (in /usr/local/Cellar/crystal-lang/0.9.0/src/tuple.cr:163):2

          yield self[0]

importation.cr

require "./importation/*"

module Importation
  def root
    ROOT
  end

  def files_path
    "#{root}/files"
  end

end

reduced.cr

h = {
  "a" => "a",
  "b" => "",
  "c" => "a",
  "d" => "",
  "e" => "a",
}

e = h.map do |k, v|
      next if v.nil? || v.empty?
      "#{k}=#{v}"
    end
pp e

root.cr

ROOT = __DIR__