standardize database_configuration to a hash

make connection_url_to_hash a class method

This als prevents loading database.yml if it doesn't exist
but DATABASE_URL does

activerecord/lib/active_record/connection_adapters/connection_specification.rb

@@ -38,7 +38,7 @@ def spec
         private
         def resolve_string_connection(spec) # :nodoc:
           hash = configurations.fetch(spec) do |k|
-            connection_url_to_hash(k)
+            self.class.connection_url_to_hash(k)
           end
 
           raise(AdapterNotSpecified, "#{spec} database is not configured") unless hash
@@ -69,7 +69,7 @@ def resolve_hash_connection(spec) # :nodoc:
         SIMPLE_INT = /\A\d+\z/
         SIMPLE_FLOAT = /\A\d+\.\d+\z/
 
-        def connection_url_to_hash(url) # :nodoc:
+        def self.connection_url_to_hash(url) # :nodoc:
           config = URI.parse url
           adapter = config.scheme
           adapter = "postgresql" if adapter == "postgres"

activerecord/lib/active_record/railtie.rb

@@ -141,9 +141,7 @@ class Railtie < Rails::Railtie # :nodoc:
     # and then establishes the connection.
     initializer "active_record.initialize_database" do |app|
       ActiveSupport.on_load(:active_record) do
-        unless ENV['DATABASE_URL']
-          self.configurations = app.config.database_configuration
-        end
+        self.configurations = app.config.database_configuration
         establish_connection
       end
     end

railties/lib/rails/application/configuration.rb

@@ -101,8 +101,12 @@ def threadsafe!
       # contents of the file are processed via ERB before being sent through
       # YAML::load.
       def database_configuration
-        require 'erb'
-        YAML.load ERB.new(IO.read(paths["config/database"].first)).result
+        if ENV['DATABASE_URL']
+          {Rails.env => ActiveRecord::ConnectionAdapters::ConnectionSpecification::Resolver.connection_url_to_hash(ENV['DATABASE_URL']).stringify_keys}
+        else
+          require 'erb'
+          YAML.load ERB.new(IO.read(paths["config/database"].first)).result
+        end
       rescue Psych::SyntaxError => e
         raise "YAML syntax error occurred while parsing #{paths["config/database"].first}. " \
               "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \