FIX: removing a group from a user was not removing primary group

app/controllers/admin/groups_controller.rb

@@ -93,9 +93,12 @@ class Admin::GroupsController < Admin::AdminController
 
     return can_not_modify_automatic if group.automatic
 
+    user = User.find(user_id)
+    user.primary_group_id = nil if user.primary_group_id == group.id
+
     group.users.delete(user_id)
 
-    if group.save
+    if group.save && user.save
       render json: success_json
     else
       render_json_error(group)

app/models/group.rb

@@ -279,6 +279,7 @@ class Group < ActiveRecord::Base
 
   def remove(user)
     self.group_users.where(user: user).each(&:destroy)
+    user.update_columns(primary_group_id: nil) if user.primary_group_id == self.id
   end
 
   def appoint_manager(user)

spec/controllers/admin/groups_controller_spec.rb

@@ -137,11 +137,17 @@ describe Admin::GroupsController do
       group.add(user)
       group.save
 
+      user.primary_group_id = group.id
+      user.save
+
       xhr :delete, :remove_member, id: group.id, user_id: user.id
 
       expect(response).to be_success
       group.reload
       expect(group.users.count).to eq(0)
+
+      user.reload
+      expect(user.primary_group_id).to eq(nil)
     end
 
   end

spec/models/group_spec.rb

@@ -47,6 +47,24 @@ describe Group do
     Group[:staff].user_ids - [-1]
   end
 
+  it "Correctly handles primary group" do
+    group = Fabricate(:group)
+    user = Fabricate(:user)
+    group.add(user)
+    group.save
+
+    user.primary_group = group
+    user.save
+
+    group.reload
+
+    group.remove(user)
+    group.save
+
+    user.reload
+    expect(user.primary_group).to eq nil
+  end
+
   it "Can update moderator/staff/admin groups correctly" do
 
     admin = Fabricate(:admin)