[MODEL] Add warning and documentation about STI support being deprecated (elastic#895)

* [MODEL] Add warning and documentation about STI support being deprecated

* [MODEL] Minor change to STI deprecation warning

* [MODEL] Freeze string constant depreaction warning

Author: estolfo

elasticsearch-model/README.md

@@ -732,13 +732,8 @@ module and its submodules for technical information.
 
 The module provides a common `settings` method to customize various features.
 
-At the moment, the only supported setting is `:inheritance_enabled`, which makes the class receiving the module
-respect index names and document types of a super-class, eg. in case you're using "single table inheritance" (STI)
-in Rails:
-
-```ruby
-Elasticsearch::Model.settings[:inheritance_enabled] = true
-```
+Before version 7.0.0 of the gem, the only supported setting was `:inheritance_enabled`. This setting has been deprecated
+and removed.
 
 ## Development and Community
 
@@ -756,6 +751,15 @@ curl -# https://download.elasticsearch.org/elasticsearch/elasticsearch/elasticse
 SERVER=start TEST_CLUSTER_COMMAND=$PWD/tmp/elasticsearch-1.0.0.RC1/bin/elasticsearch bundle exec rake test:all
 ```
 
+### Single Table Inheritance support
+
+Versions < 7.0.0 of this gem supported inheritance-- more specifically, `Single Table Inheritance`. With this feature,
+settings on a parent model could be inherited by a child model leading to different model documents being indexed
+into the same Elasticsearch index. This feature depended on the ability to set a `type` for a document in Elasticsearch.
+The Elasticsearch team has deprecated support for `types`, as is described [here](https://www.elastic.co/guide/en/elasticsearch/reference/current/removal-of-types.html)
+so this gem has also removed support as it encourages an anti-pattern. Please save different model documents in
+separate indices or implement an artificial `type` field manually in each document.
+
 ## License
 
 This software is licensed under the Apache 2 license, quoted below.

elasticsearch-model/lib/elasticsearch/model.rb

@@ -121,12 +121,6 @@ class << self
       Registry.add(base) if base.is_a?(Class)
     end
 
-    # Access the module settings
-    #
-    def self.settings
-      @settings ||= {}
-    end
-
     module ClassMethods
       # Get the client common for all models
       #
@@ -183,7 +177,7 @@ def search(query_or_payload, models=[], options={})
       # @note Inheritance is disabled by default.
       #
       def inheritance_enabled
-        @inheritance_enabled ||= false
+        @settings[:inheritance_enabled] ||= false
       end
 
       # Enable inheritance of index_name and document_type
@@ -193,8 +187,21 @@ def inheritance_enabled
       #     Elasticsearch::Model.inheritance_enabled = true
       #
       def inheritance_enabled=(inheritance_enabled)
-        @inheritance_enabled = inheritance_enabled
+        warn STI_DEPRECATION_WARNING
+        @settings[:inheritance_enabled] = inheritance_enabled
+      end
+
+      # Access the module settings
+      #
+      def settings
+        @settings ||= {}
       end
+
+      private
+
+      STI_DEPRECATION_WARNING = "DEPRECATION WARNING: Support for Single Table Inheritance (STI) is deprecated " +
+        "and will be removed in version 7.0.0.\nPlease save different model documents in separate indices and refer " +
+        "to the Elasticsearch documentation for more information.".freeze
     end
     extend ClassMethods
 

elasticsearch-model/spec/elasticsearch/model/naming_inheritance_spec.rb

@@ -61,10 +61,10 @@ module ::MyNamespace
     end
 
     around(:all) do |example|
-      original_value = Elasticsearch::Model.settings[:inheritance_enabled]
-      Elasticsearch::Model.settings[:inheritance_enabled] = true
+      original_value = Elasticsearch::Model.inheritance_enabled
+      Elasticsearch::Model.inheritance_enabled = true
       example.run
-      Elasticsearch::Model.settings[:inheritance_enabled] = original_value
+      Elasticsearch::Model.inheritance_enabled = original_value
     end