Add opportunity for chain of configuration from initializers to concerns and models. Based on railsadminteam#1781

Author: semenovDL

lib/rails_admin/config.rb

@@ -226,11 +226,9 @@ def model(entity, &block)
           end
         end
 
-        if block
-          @registry[key] = RailsAdmin::Config::LazyModel.new(entity, &block)
-        else
-          @registry[key] ||= RailsAdmin::Config::LazyModel.new(entity)
-        end
+        @registry[key] ||= RailsAdmin::Config::LazyModel.new(entity)
+        @registry[key].add_deferred_block(&block) if block
+        @registry[key]
       end
 
       def default_hidden_fields=(fields)

lib/rails_admin/config/lazy_model.rb

@@ -5,13 +5,48 @@ module Config
     class LazyModel < BasicObject
       def initialize(entity, &block)
         @entity = entity
-        @deferred_block = block
+        @deferred_blocks = [*block]
+      end
+
+      def add_deferred_block(&block)
+        @deferred_blocks << block
       end
 
       def target
         unless @model
           @model = ::RailsAdmin::Config::Model.new(@entity)
-          @model.instance_eval(&@deferred_block) if @deferred_block
+          # When evaluating multiple configuration blocks, the order of
+          # execution is important. As one would expect (in my opinion),
+          # options defined within a resource should take precedence over
+          # more general options defined in an initializer. This way,
+          # general settings for a number of resources could be specified
+          # in the initializer, while models could override these settings
+          # later, if required.
+          #
+          # CAVEAT: It cannot be guaranteed that blocks defined in an initializer
+          # will be loaded (and adde to @deferred_blocks) first. For instance, if
+          # the initializer references a model class before defining
+          # a RailsAdmin configuration block, the configuration from the
+          # resource will get added to @deferred_blocks first:
+          #
+          #     # app/models/some_model.rb
+          #     class SomeModel
+          #       rails_admin do
+          #         :
+          #       end
+          #     end
+          #
+          #     # config/initializers/rails_admin.rb
+          #     model = 'SomeModel'.constantize # blocks from SomeModel get loaded
+          #     model.config model do           # blocks from initializer gets loaded
+          #       :
+          #     end
+          #
+          # Thus, sort all blocks to excute for a resource by Proc.source_path,
+          # to guarantee that blocks from 'config/initializers' evaluate before
+          # blocks defined within a model class.
+          @deferred_blocks.partition { |block| block.source_location.first =~ /config\/initializers/ }
+                          .flatten.each { |block| @model.instance_eval(&block) }
         end
         @model
       end