Virtual/generated column support for MySQL 5.7.5+ and MariaDB 5.2.0+

MySQL generated columns: https://dev.mysql.com/doc/refman/5.7/en/create-table-generated-columns.html
MariaDB virtual columns: https://mariadb.com/kb/en/mariadb/virtual-computed-columns/

Declare virtual columns with `t.virtual name, type: …, as: "expression"`.
Pass `stored: true` to persist the generated value (false by default).

Example:

    create_table :generated_columns do |t|
      t.string  :name
      t.virtual :upper_name, type: :string,  as: "UPPER(name)"
      t.virtual :name_length, type: :integer, as: "LENGTH(name)", stored: true
      t.index :name_length  # May be indexed, too!
    end

Closes #22589

1 files changed, 14 insertions, 10 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
index f1ba0cb708..76ebd0bf6c 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
@@ -3,8 +3,7 @@ module ActiveRecord
     module MySQL
       module ColumnMethods
         def primary_key(name, type = :primary_key, **options)
-          options[:auto_increment] = true if [:primary_key, :integer, :bigint].include?(type) && !options.key?(:default)
-          options[:limit] = 8 if [:primary_key].include?(type)
+          options[:auto_increment] = true if [:integer, :bigint].include?(type) && !options.key?(:default)
           super
         end
 
@@ -58,24 +57,29 @@ module ActiveRecord
       end
 
       class ColumnDefinition < ActiveRecord::ConnectionAdapters::ColumnDefinition
-        attr_accessor :charset, :unsigned
+        attr_accessor :charset, :unsigned, :stored
       end
 
       class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         include ColumnMethods
 
         def new_column_definition(name, type, options) # :nodoc:
-          column = super
-          case column.type
+          case type
+          when :virtual
+            type = options[:type]
           when :primary_key
-            column.type = :integer
-            column.auto_increment = true
+            type = :integer
+            options[:limit] ||= 8
+            options[:auto_increment] = true
+            options[:primary_key] = true
           when /\Aunsigned_(?<type>.+)\z/
-            column.type = $~[:type].to_sym
-            column.unsigned = true
+            type = $~[:type].to_sym
+            options[:unsigned] = true
           end
-          column.unsigned ||= options[:unsigned]
+          column = super
+          column.unsigned = options[:unsigned]
           column.charset = options[:charset]
+          column.stored = options[:stored]
           column
         end