Allow 3-level DB configs to group connections by environment

[Arthur Nogueira Neves & Matthew Draper]

activerecord/lib/active_record/connection_adapters/connection_specification.rb

@@ -149,9 +149,18 @@ def resolve(config)
         # Expands each key in @configurations hash into fully resolved hash
         def resolve_all
           config = configurations.dup
+
+          if env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+            env_config = config[env] if config[env].is_a?(Hash) && !(config[env].key?("adapter") || config[env].key?("url"))
+          end
+
+          config.reject! { |k, v| v.is_a?(Hash) && !(v.key?("adapter") || v.key?("url")) }
+          config.merge! env_config if env_config
+
           config.each do |key, value|
             config[key] = resolve(value) if value
           end
+
           config
         end
 

activerecord/test/cases/connection_adapters/connection_handler_test.rb

@@ -20,6 +20,66 @@ def test_establish_connection_uses_spec_name
         @handler.remove_connection("readonly")
       end
 
+      def test_establish_connection_using_3_levels_config
+        previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+        config = {
+          "default_env" => {
+            "readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" },
+            "primary"  => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" }
+          },
+          "another_env" => {
+            "readonly" => { "adapter" => "sqlite3", "database" => "db/bad-readonly.sqlite3" },
+            "primary"  => { "adapter" => "sqlite3", "database" => "db/bad-primary.sqlite3" }
+          },
+          "common" => { "adapter" => "sqlite3", "database" => "db/common.sqlite3" }
+        }
+        @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+        @handler.establish_connection(:common)
+        @handler.establish_connection(:primary)
+        @handler.establish_connection(:readonly)
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("readonly")
+        assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("primary")
+        assert_equal "db/primary.sqlite3", pool.spec.config[:database]
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("common")
+        assert_equal "db/common.sqlite3", pool.spec.config[:database]
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+        ENV["RAILS_ENV"] = previous_env
+      end
+
+      def test_establish_connection_using_two_level_configurations
+        config = { "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" } }
+        @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+        @handler.establish_connection(:development)
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("development")
+        assert_equal "db/primary.sqlite3", pool.spec.config[:database]
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+      end
+
+      def test_establish_connection_using_top_level_key_in_two_level_config
+        config = {
+          "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" },
+          "development_readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
+        }
+        @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+        @handler.establish_connection(:development_readonly)
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("development_readonly")
+        assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+      end
+
       def test_retrieve_connection
         assert @handler.retrieve_connection(@spec_name)
       end