Merge branch 'dz-nested-groups' into 'master'

Add nested groups support on data level

## What does this MR do?

- [x] Add  `parent_id` field to `Namespace`model. 
- [x] Create new database table `routes` that keeps information about full path to each group or project
- [x] Remove uniq index from `namespaces.path`
- [x] Add uniq index on `routes.path`
- [x] Fill routes table with path data from namespaces and projects
- [x] Change Namespace/Project URL lookup by routes table
- [x] Rename related routes (nested groups, projects) when parent path changes

This is solely backend preparation. UI, Permissions and API support will be added in separate merge request.   
 
## Are there points in the code the reviewer needs to double check?

migrations, Route model, Routable concern

Will require downtime. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7121#note_19490281 discussion

## Why was this MR needed?

One step further to full nested groups support

## Screenshots (if relevant)

No UI changes in this merge request so far

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added~~
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/2772

See merge request !7121

1 files changed, 17 insertions, 1 deletions

diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index 7a545f752b6..37374044551 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -4,12 +4,16 @@ class Namespace < ActiveRecord::Base
   include CacheMarkdownField
   include Sortable
   include Gitlab::ShellAdapter
+  include Routable
 
   cache_markdown_field :description, pipeline: :description
 
   has_many :projects, dependent: :destroy
   belongs_to :owner, class_name: "User"
 
+  belongs_to :parent, class_name: "Namespace"
+  has_many :children, class_name: "Namespace", foreign_key: :parent_id
+
   validates :owner, presence: true, unless: ->(n) { n.type == "Group" }
   validates :name,
     presence: true,
@@ -86,7 +90,7 @@ class Namespace < ActiveRecord::Base
   end
 
   def to_param
-    path
+    full_path
   end
 
   def human_name
@@ -150,6 +154,14 @@ class Namespace < ActiveRecord::Base
     Gitlab.config.lfs.enabled
   end
 
+  def full_path
+    if parent
+      parent.full_path + '/' + path
+    else
+      path
+    end
+  end
+
   private
 
   def repository_storage_paths
@@ -185,4 +197,8 @@ class Namespace < ActiveRecord::Base
       where(projects: { namespace_id: id }).
       find_each(&:refresh_members_authorized_projects)
   end
+
+  def full_path_changed?
+    path_changed? || parent_id_changed?
+  end
 end