Use subqueries to find nested members more efficiently

app/controllers/api/nodes/relations_controller.rb

@@ -6,13 +6,12 @@ module Api
       before_action :set_request_formats
 
       def index
-        relation_ids = RelationMember.where(:member_type => "Node", :member_id => params[:node_id]).collect(&:relation_id).uniq
+        @relations = Relation
-
+                     .visible
-        @relations = []
+                     .where(:id => RelationMember.where(
-
+                       :member_type => "Node",
-        Relation.find(relation_ids).each do |relation|
+                       :member_id => params[:node_id]
-          @relations << relation if relation.visible
+                     ).select(:relation_id))
-        end
 
         # Render the result
         respond_to do |format|

app/controllers/api/nodes/ways_controller.rb

@@ -10,9 +10,11 @@ module Api
       # :node_id parameter. note that this used to return deleted ways as well, but
       # this seemed not to be the expected behaviour, so it was removed.
       def index
-        way_ids = WayNode.where(:node_id => params[:node_id]).collect { |ws| ws.id[0] }.uniq
+        @ways = Way
-
+                .visible
-        @ways = Way.where(:id => way_ids, :visible => true)
+                .where(:id => WayNode.where(
+                  :node_id => params[:node_id]
+                ).select(:way_id))
 
         # Render the result
         respond_to do |format|

app/controllers/api/relations/relations_controller.rb

@@ -6,13 +6,12 @@ module Api
       before_action :set_request_formats
 
       def index
-        relation_ids = RelationMember.where(:member_type => "Relation", :member_id => params[:relation_id]).collect(&:relation_id).uniq
+        @relations = Relation
-
+                     .visible
-        @relations = []
+                     .where(:id => RelationMember.where(
-
+                       :member_type => "Relation",
-        Relation.find(relation_ids).each do |relation|
+                       :member_id => params[:relation_id]
-          @relations << relation if relation.visible
+                     ).select(:relation_id))
-        end
 
         # Render the result
         respond_to do |format|

app/controllers/api/ways/relations_controller.rb

@@ -6,13 +6,12 @@ module Api
       before_action :set_request_formats
 
       def index
-        relation_ids = RelationMember.where(:member_type => "Way", :member_id => params[:way_id]).collect(&:relation_id).uniq
+        @relations = Relation
-
+                     .visible
-        @relations = []
+                     .where(:id => RelationMember.where(
-
+                       :member_type => "Way",
-        Relation.find(relation_ids).each do |relation|
+                       :member_id => params[:way_id]
-          @relations << relation if relation.visible
+                     ).select(:relation_id))
-        end
 
         # Render the result
         respond_to do |format|