Support creating a table migration generator

Sometimes you want to create a table without an associated model and
test, which is also not a join table. With this commit, you can now
do that.

Example:

    rails g migration create_posts title:string
or
    rails g migration CreatePosts title:string

This commit also moves the template the model generator uses for the
migration to the migration templates folder, as it seems a more
sensible place for it now that it is shared code.

activerecord/CHANGELOG.md

@@ -1,5 +1,15 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Added support for creating a table via Rails migration generator.
+    For example, 
+
+        rails g migration create_books title:string content:text
+
+    will generate a migration that creates a table called books with 
+    the listed attributes, without creating a model. 
+
+    *Sammy Larbi*
+
 *   Fix bug that raises the wrong exception when the exception handled by PostgreSQL adapter
     doesn't respond to `#result`.
     Fixes #8617.
@@ -362,7 +372,7 @@
     deprecated and removed in future versions of Rails.
 
     *Amparo Luna + Guillermo Iguaran*
-
+    
 *   `after_commit` and `after_rollback` now validate the `:on` option and raise an `ArgumentError`
     if it is not one of `:create`, `:destroy` or `:update`
 
@@ -1549,4 +1559,5 @@
 
     *Aaron Patterson*
 
+
 Please check [3-2-stable](https://github.com/rails/rails/blob/3-2-stable/activerecord/CHANGELOG.md) for previous changes.

activerecord/lib/rails/generators/active_record/migration/migration_generator.rb

@@ -8,13 +8,14 @@ module ActiveRecord
       def create_migration_file
         set_local_assigns!
         validate_file_name!
-        migration_template "migration.rb", "db/migrate/#{file_name}.rb"
+        migration_template @migration_template, "db/migrate/#{file_name}.rb"
       end
 
       protected
       attr_reader :migration_action, :join_tables
 
       def set_local_assigns!
+        @migration_template = "migration.rb"
         case file_name
         when /^(add|remove)_.*_(?:to|from)_(.*)/
           @migration_action = $1
@@ -26,6 +27,9 @@ module ActiveRecord
 
             set_index_names
           end
+        when /^create_(.+)/
+          @table_name = $1.pluralize
+          @migration_template = "create_table_migration.rb"
         end
       end
 
@@ -44,7 +48,10 @@ module ActiveRecord
       end
 
       private
-
+        def attributes_with_index
+          attributes.select { |a| !a.reference? && a.has_index? }
+        end
+        
         def validate_file_name!
           unless file_name =~ /^[_a-z0-9]+$/
             raise IllegalMigrationNameError.new(file_name)

activerecord/lib/rails/generators/active_record/model/model_generator.rb

@@ -15,7 +15,7 @@ module ActiveRecord
       def create_migration_file
         return unless options[:migration] && options[:parent].nil?
         attributes.each { |a| a.attr_options.delete(:index) if a.reference? && !a.has_index? } if options[:indexes] == false
-        migration_template "migration.rb", "db/migrate/create_#{table_name}.rb"
+        migration_template "../../migration/templates/create_table_migration.rb", "db/migrate/create_#{table_name}.rb"
       end
 
       def create_model_file

guides/source/migrations.md

@@ -179,6 +179,27 @@ class AddDetailsToProducts < ActiveRecord::Migration
 end
 ```
 
+If the migration name is of the form "CreateXXX" and is
+followed by a list of column names and types then a migration creating the table 
+XXX with the columns listed will be generated. For example:
+
+```bash
+$ rails generate migration CreateProducts name:string part_number:string
+```
+
+generates
+
+```ruby
+class CreateProducts < ActiveRecord::Migration
+  def change
+    create_table :products do |t|
+      t.string :name
+      t.string :part_number
+    end
+  end
+end
+```
+
 As always, what has been generated for you is just a starting point. You can add
 or remove from it as you see fit by editing the
 `db/migrate/YYYYMMDDHHMMSS_add_details_to_products.rb` file.

railties/test/generators/migration_generator_test.rb

@@ -172,8 +172,19 @@ class MigrationGeneratorTest < Rails::Generators::TestCase
     end
   end
 
-  def test_should_create_empty_migrations_if_name_not_start_with_add_or_remove
-    migration = "create_books"
+  def test_create_table_migration
+    run_generator ["create_books", "title:string", "content:text"]
+    assert_migration "db/migrate/create_books.rb" do |content|
+      assert_method :change, content do |change|
+        assert_match(/create_table :books/, change)
+        assert_match(/  t\.string :title/, change)
+        assert_match(/  t\.text :content/, change)
+      end
+    end
+  end
+
+  def test_should_create_empty_migrations_if_name_not_start_with_add_or_remove_or_create
+    migration = "delete_books"
     run_generator [migration, "title:string", "content:text"]
 
     assert_migration "db/migrate/#{migration}.rb" do |content|
@@ -182,7 +193,7 @@ class MigrationGeneratorTest < Rails::Generators::TestCase
       end
     end
   end
-
+  
   def test_properly_identifies_usage_file
     assert generator_class.send(:usage_path)
   end