Allow categories with null position, which means sort them based on activity. Mix absolutely positioned (position is not null) categories with null position categories.

app/assets/javascripts/discourse/controllers/edit_category_controller.js

@@ -12,6 +12,7 @@ Discourse.EditCategoryController = Discourse.ObjectController.extend(Discourse.M
   securitySelected: Ember.computed.equal('selectedTab', 'security'),
   settingsSelected: Ember.computed.equal('selectedTab', 'settings'),
   foregroundColors: ['FFFFFF', '000000'],
+  defaultPosition:  false,
 
   parentCategories: function() {
     return Discourse.Category.list().filter(function (c) {
@@ -22,6 +23,7 @@ Discourse.EditCategoryController = Discourse.ObjectController.extend(Discourse.M
   onShow: function() {
     this.changeSize();
     this.titleChanged();
+    this.set('defaultPosition', this.get('position') === null);
   },
 
   changeSize: function() {
@@ -127,6 +129,17 @@ Discourse.EditCategoryController = Discourse.ObjectController.extend(Discourse.M
       this.get('model').removePermission(permission);
     },
 
+    toggleDefaultPosition: function() {
+      this.toggleProperty('defaultPosition');
+    },
+
+    disableDefaultPosition: function() {
+      this.set('defaultPosition', false);
+      Em.run.schedule('afterRender', function() {
+        this.$('.position-input').focus();
+      });
+    },
+
     saveCategory: function() {
       var self = this,
           model = this.get('model'),
@@ -134,6 +147,7 @@ Discourse.EditCategoryController = Discourse.ObjectController.extend(Discourse.M
 
       this.set('saving', true);
       model.set('parentCategory', parentCategory);
+      if (this.get('defaultPosition')) { model.set('position', 'default'); }
 
       self.set('saving', false);
       this.get('model').save().then(function(result) {

app/assets/javascripts/discourse/templates/modal/edit_category.js.handlebars

@@ -100,7 +100,12 @@
 
         <section class='field'>
           <label>{{i18n category.position}}</label>
-          {{textField value=position}}
+          <span {{action disableDefaultPosition}}>{{textField value=position disabled=defaultPosition class="position-input"}}</span>
+          &nbsp;{{i18n or}}&nbsp;
+          <button {{bindAttr class=":btn defaultPosition:btn-primary"}} {{action toggleDefaultPosition}}>
+            <span {{bindAttr class="defaultPosition::hidden"}}><i class="fa fa-check"></i></span>
+            {{i18n category.default_position}}
+          </button>
         </section>
 
         <section class='field'>

app/controllers/categories_controller.rb

@@ -60,7 +60,9 @@ class CategoriesController < ApplicationController
   def update
     guardian.ensure_can_edit!(@category)
     json_result(@category, serializer: CategorySerializer) { |cat|
-      cat.move_to(category_params[:position].to_i) if category_params[:position]
+      if category_params[:position]
+        category_params[:position] == 'default' ? cat.use_default_position : cat.move_to(category_params[:position].to_i)
+      end
       category_params.delete(:position)
       cat.update_attributes(category_params)
     }

app/models/category.rb

@@ -364,7 +364,7 @@ end
 #  post_count         :integer          default(0), not null
 #  latest_post_id     :integer
 #  latest_topic_id    :integer
-#  position           :integer          not null
+#  position           :integer
 #  parent_category_id :integer
 #
 # Indexes

app/models/category_list.rb

@@ -53,23 +53,36 @@ class CategoryList
 
     # Find a list of all categories to associate the topics with
     def find_categories
-      @categories = Category
+      @absolute_position_categories = Category
-                      .includes(:featured_users)
+                                        .includes(:featured_users)
-                      .secured(@guardian)
+                                        .secured(@guardian)
-                      .order('position ASC')
+                                        .where('position IS NOT NULL')
+                                        .order('position ASC')
+      @default_position_categories = Category
+                                        .includes(:featured_users)
+                                        .secured(@guardian)
+                                        .where('position IS NULL')
+                                        .order('COALESCE(categories.posts_week, 0) DESC')
+                                        .order('COALESCE(categories.posts_month, 0) DESC')
+                                        .order('COALESCE(categories.posts_year, 0) DESC')
 
       if latest_post_only?
-        @categories = @categories.includes(:latest_post => {:topic => :last_poster} )
+        @absolute_position_categories = @absolute_position_categories.includes(:latest_post => {:topic => :last_poster} )
-      # else
+        @default_position_categories  = @default_position_categories.includes(:latest_post => {:topic => :last_poster} )
-      #   # This is only for the old 2-column layout.
-      #   # Use this when we support "organic" positioning of some/all categories.
-      #   @categories = @categories
-      #                   .order('COALESCE(categories.topics_week, 0) DESC')
-      #                   .order('COALESCE(categories.topics_month, 0) DESC')
-      #                   .order('COALESCE(categories.topics_year, 0) DESC')
       end
 
-      @categories = @categories.to_a
+      @default_position_categories = @default_position_categories.to_a
+      @categories = []
+      index = 0
+      @absolute_position_categories.to_a.each do |c|
+        if c.position > index
+          @categories.push(*(@default_position_categories.shift(c.position - index)))
+        end
+        @categories << c
+        index = c.position + 1 if c.position >= index # handles duplicate position values
+      end
+      @categories.push *@default_position_categories # Whatever is left is put on the end
+
 
       subcategories = {}
       to_delete = Set.new

config/locales/client.en.yml

@@ -1007,6 +1007,7 @@ en:
       add_permission: "Add Permission"
       this_year: "this year"
       position: "position"
+      default_position: "Default Position"
       parent: "Parent Category"
 
     flagging:

db/migrate/20131216164557_make_position_nullable_in_categories.rb

@@ -0,0 +1,10 @@
+class MakePositionNullableInCategories < ActiveRecord::Migration
+  def up
+    change_column :categories, :position, :integer, null: true
+  end
+
+  def down
+    execute "update categories set position=0 where position is null"
+    change_column :categories, :position, :integer, null: false
+  end
+end

lib/concern/positionable.rb

@@ -2,36 +2,38 @@ module Concern
   module Positionable
     extend ActiveSupport::Concern
 
-    included do
+    def move_to(position_arg)
-      before_save do
+
-        self.position ||= self.class.count
+      position = [[position_arg, 0].max, self.class.count - 1].min
+
+      if self.position.nil? or position > self.position
+        self.exec_sql "
+        UPDATE #{self.class.table_name}
+        SET position = position - 1
+        WHERE position > :current_position and position <= :new_position",
+        {current_position: self.position, new_position: position}
+      elsif position < self.position
+        self.exec_sql "
+        UPDATE #{self.class.table_name}
+        SET position = position + 1
+        WHERE position >= :new_position and position < :current_position",
+        {current_position: self.position, new_position: position}
+      else
+        # Not moving to a new position
+        return
       end
-    end
-
-    def move_to(position)
-
-      self.exec_sql "
-      UPDATE #{self.class.table_name}
-      SET position = position - 1
-      WHERE position > :position AND position > 0", {position: self.position}
 
       self.exec_sql "
       UPDATE #{self.class.table_name}
       SET position = :position
       WHERE id = :id", {id: id, position: position}
+    end
 
+    def use_default_position
       self.exec_sql "
-      UPDATE #{self.class.table_name} t
+      UPDATE #{self.class.table_name}
-      SET position = x.position - 1
+      SET POSITION = null
-      FROM (
+      WHERE id = :id", {id: id}
-        SELECT i.id, row_number()
-          OVER(ORDER BY i.position asc,
-                        CASE WHEN i.id = :id THEN 0 ELSE 1 END ASC) AS position
-        FROM #{self.class.table_name} i
-        WHERE i.position IS NOT NULL
-      ) x
-      WHERE x.id = t.id AND t.position <> x.position - 1
-      ", {id: id}
     end
   end
 end

spec/components/category_list_spec.rb

@@ -4,11 +4,11 @@ require 'category_list'
 describe CategoryList do
 
   let(:user) { Fabricate(:user) }
+  let(:admin) { Fabricate(:admin) }
   let(:category_list) { CategoryList.new(Guardian.new user) }
 
   context "security" do
     it "properly hide secure categories" do
-      admin = Fabricate(:admin)
       user = Fabricate(:user)
 
       cat = Fabricate(:category)
@@ -73,4 +73,35 @@ describe CategoryList do
 
   end
 
+  describe 'category order' do
+    let(:category_ids) { CategoryList.new(Guardian.new(admin)).categories.map(&:id) - [SiteSetting.uncategorized_category_id] }
+
+    before do
+      uncategorized = Category.find(SiteSetting.uncategorized_category_id)
+      uncategorized.position = 100
+      uncategorized.save
+    end
+
+    it "returns topics in specified order" do
+      cat1, cat2 = Fabricate(:category, position: 1), Fabricate(:category, position: 0)
+      category_ids.should == [cat2.id, cat1.id]
+    end
+
+    it "returns default order categories" do
+      cat1, cat2 = Fabricate(:category, position: nil), Fabricate(:category, position: nil)
+      category_ids.should include(cat1.id)
+      category_ids.should include(cat2.id)
+    end
+
+    it "mixes default order categories with absolute position categories" do
+      cat1, cat2, cat3 = Fabricate(:category, position: 0), Fabricate(:category, position: 2), Fabricate(:category, position: nil)
+      category_ids.should == [cat1.id, cat3.id, cat2.id]
+    end
+
+    it "handles duplicate position values" do
+      cat1, cat2, cat3, cat4 = Fabricate(:category, position: 0), Fabricate(:category, position: 0), Fabricate(:category, position: nil), Fabricate(:category, position: 0)
+      category_ids.should == [cat1.id, cat2.id, cat4.id, cat3.id]
+    end
+  end
+
 end

spec/components/concern/positionable_spec.rb

@@ -37,8 +37,7 @@ describe Concern::Positionable do
       TestItem.find(3).move_to(1)
       positions.should == [0,3,1,2,4]
 
-      # this is somewhat odd, but when there is not positioning
+      # this is somewhat odd, but when there is no such position, not much we can do
-      # not much we can do
       TestItem.find(1).move_to(5)
       positions.should == [0,3,2,4,1]
 
@@ -47,7 +46,34 @@ describe Concern::Positionable do
       item = TestItem.new
       item.id = 7
       item.save
-      item.position.should == 5
+      item.position.should be_nil
+    end
+
+    it "can set records to have null position" do
+      5.times do |i|
+        Topic.exec_sql("insert into test_items(id,position) values(#{i}, #{i})")
+      end
+
+      TestItem.find(2).use_default_position
+      TestItem.find(2).position.should be_nil
+
+      TestItem.find(1).move_to(4)
+      TestItem.order('id ASC').pluck(:position).should == [0,4,nil,2,3]
+    end
+
+    it "can maintain null positions when moving things around" do
+      5.times do |i|
+        Topic.exec_sql("insert into test_items(id,position) values(#{i}, null)")
+      end
+
+      TestItem.find(2).move_to(0)
+      TestItem.order('id asc').pluck(:position).should == [nil,nil,0,nil,nil]
+      TestItem.find(0).move_to(4)
+      TestItem.order('id asc').pluck(:position).should == [4,nil,0,nil,nil]
+      TestItem.find(2).move_to(1)
+      TestItem.order('id asc').pluck(:position).should == [4,nil,1,nil,nil]
+      TestItem.find(0).move_to(1)
+      TestItem.order('id asc').pluck(:position).should == [1,nil,2,nil,nil]
     end
   end
 end

spec/controllers/categories_controller_spec.rb

@@ -105,6 +105,8 @@ describe CategoriesController do
 
 
     describe "logged in" do
+      let(:valid_attrs) { {id: @category.id, name: "hello", color: "ff0", text_color: "fff"} }
+
       before do
         @user = log_in(:moderator)
         @category = Fabricate(:category, user: @user)
@@ -146,7 +148,6 @@ describe CategoriesController do
       describe "success" do
 
         it "updates the group correctly" do
-
           readonly = CategoryGroup.permission_types[:readonly]
           create_post = CategoryGroup.permission_types[:create_post]
 
@@ -167,7 +168,13 @@ describe CategoriesController do
           @category.color.should == "ff0"
           @category.hotness.should == 2
           @category.auto_close_hours.should == 72
+        end
 
+        it "can set category to use default position" do
+          xhr :put, :update, valid_attrs.merge(position: 'default')
+          response.should be_success
+          @category.reload
+          @category.position.should be_nil
         end
       end
     end