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Diffstat (limited to 'guides')
| -rw-r--r-- | guides/source/migrations.textile | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/guides/source/migrations.textile b/guides/source/migrations.textile index 342b5a4d57..06e85e5914 100644 --- a/guides/source/migrations.textile +++ b/guides/source/migrations.textile @@ -111,6 +111,7 @@ Active Record provides methods that perform common data definition tasks in a database independent way (you'll read about them in detail later): * +add_column+ +* +add_reference+ * +add_index+ * +change_column+ * +change_table+ @@ -120,6 +121,7 @@ database independent way (you'll read about them in detail later): * +remove_column+ * +remove_index+ * +rename_column+ +* +remove_reference+ If you need to perform tasks specific to your database (for example create a "foreign key":#active-record-and-referential-integrity constraint) then the @@ -332,6 +334,51 @@ NOTE: The generated migration file for destructive migrations will still be old-style using the +up+ and +down+ methods. This is because Rails needs to know the original data types defined when you made the original changes. +Also the generator accepts column type as +references+(also available as +belongs_to+), for instance + +<shell> +$ rails generate migration AddUserRefToProducts user:references +</shell> + +generates + +<ruby> +class AddUserRefToProducts < ActiveRecord::Migration + def change + add_reference :products, :user, :index => true + end +end +</ruby> + +This migration will create a user_id column and appropriate index. + +h4. Supported type modifiers + +You can also specify some options just after the field type between curly braces. You can use the +following modifiers: + +* +limit+ Sets the maximum size of the +string/text/binary/integer+ fields +* +precision+ Defines the precision for the +decimal+ fields +* +scale+ Defines the scale for the +decimal+ fields +* +polymorphic+ Adds a +type+ column for +belongs_to+ associations + +For instance running + +<shell> +$ rails generate migration AddDetailsToProducts price:decimal{5,2} supplier:references{polymorphic} +</shell> + +will produce a migration that looks like this + +<ruby> +class AddDetailsToProducts < ActiveRecord::Migration + def change + add_column :products, :price, :precision => 5, :scale => 2 + add_reference :products, :user, :polymorphic => true, :index => true + end +end +</ruby> + h3. Writing a Migration Once you have created your migration using one of the generators it's time to |