1 files changed, 24 insertions, 6 deletions
diff --git a/activerecord/lib/active_record/database_configurations.rb b/activerecord/lib/active_record/database_configurations.rb
index 73adf66684..c36b87829e 100644
--- a/activerecord/lib/active_record/database_configurations.rb
+++ b/activerecord/lib/active_record/database_configurations.rb
@@ -102,6 +102,7 @@ module ActiveRecord
 
       def build_configs(configs)
         return configs.configurations if configs.is_a?(DatabaseConfigurations)
+        return configs if configs.is_a?(Array)
 
         build_db_config = configs.each_pair.flat_map do |env_name, config|
           walk_configs(env_name.to_s, "primary", config)
@@ -166,21 +167,38 @@ module ActiveRecord
       end
 
       def method_missing(method, *args, &blk)
-        if Hash.method_defined?(method)
-          ActiveSupport::Deprecation.warn \
-            "Returning a hash from ActiveRecord::Base.configurations is deprecated. Therefore calling `#{method}` on the hash is also deprecated. Please switch to using the `configs_for` method instead to collect and iterate over database configurations."
-        end
-
         case method
         when :each, :first
+          throw_getter_deprecation(method)
           configurations.send(method, *args, &blk)
         when :fetch
+          throw_getter_deprecation(method)
           configs_for(env_name: args.first)
         when :values
+          throw_getter_deprecation(method)
           configurations.map(&:config)
+        when :[]=
+          throw_setter_deprecation(method)
+
+          env_name = args[0]
+          config = args[1]
+
+          remaining_configs = configurations.reject { |db_config| db_config.env_name == env_name }
+          new_config = build_configs(env_name => config)
+          new_configs = remaining_configs + new_config
+
+          ActiveRecord::Base.configurations = new_configs
         else
-          super
+          raise NotImplementedError, "`ActiveRecord::Base.configurations` in Rails 6 now returns an object instead of a hash. The #{method} method is not supported. Please use `configs_for` or consult the documentation for supported methods."
         end
       end
+
+      def throw_setter_deprecation(method)
+        ActiveSupport::Deprecation.warn("Setting `ActiveRecord::Base.configurations` with `#{method}` is deprecated. Use `ActiveRecord::Base.configurations=` directly to set the configurations instead.")
+      end
+
+      def throw_getter_deprecation(method)
+        ActiveSupport::Deprecation.warn("`ActiveRecord::Base.configurations` no longer returns a hash. Methods that act on the hash like `#{method}` are deprecated and will be removed in Rails 6.1. Use the `configs_for` method to collect and iterate over the database configurations.")
+      end
   end
 end