Add references schema statements

Examples:

    add_reference :products, :supplier, polymorphic: true, index: true
    remove_reference :products, :user

`add_belongs_to` and `remove_belongs_to` are
acceptable.

1 files changed, 37 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 2b0ba2f479..8e43193f4b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -441,6 +441,43 @@ module ActiveRecord
         indexes(table_name).detect { |i| i.name == index_name }
       end
 
+      # Adds a reference. Optionally adds a +type+ column, if <tt>:polymorphic</tt> option is provided.
+      # <tt>add_reference</tt> and <tt>add_belongs_to</tt> are acceptable.
+      #
+      # ====== Create a user_id column
+      #  add_reference(:products, :user)
+      #
+      # ====== Create a supplier_id and supplier_type columns
+      #  add_belongs_to(:products, :supplier, polymorphic: true)
+      #
+      # ====== Create a supplier_id, supplier_type columns and appropriate index
+      #  add_reference(:products, :supplier, polymorphic: true, index: true)
+      #
+      def add_reference(table_name, ref_name, options = {})
+        polymorphic = options.delete(:polymorphic)
+        index_options = options.delete(:index)
+        add_column(table_name, "#{ref_name}_id", :integer, options)
+        add_column(table_name, "#{ref_name}_type", :string, polymorphic.is_a?(Hash) ? polymorphic : options) if polymorphic
+        add_index(table_name, polymorphic ? %w[id type].map{ |t| "#{ref_name}_#{t}" } : "#{ref_name}_id", index_options.is_a?(Hash) ? index_options : nil) if index_options
+      end
+      alias :add_belongs_to :add_reference
+
+      # Removes the reference(s). Also removes a +type+ column if one exists.
+      # <tt>remove_reference</tt>, <tt>remove_references</tt> and <tt>remove_belongs_to</tt> are acceptable.
+      #
+      # ====== Remove the reference
+      #  remove_reference(:products, :user, index: true)
+      #
+      # ====== Remove polymorphic reference
+      #  remove_reference(:products, :supplier, polymorphic: true)
+      #
+      def remove_reference(table_name, ref_name, options = {})
+        polymorphic = options.delete(:polymorphic)
+        remove_column(table_name, "#{ref_name}_id")
+        remove_column(table_name, "#{ref_name}_type") if polymorphic
+      end
+      alias :remove_belongs_to :remove_reference
+
       # Returns a string of <tt>CREATE TABLE</tt> SQL statement(s) for recreating the
       # entire structure of the database.
       def structure_dump