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Majority of cases, where Active Record knows how to reverse the migrationĪutomatically. The change method is the primary way of writing migrations. (which provides the methods available on the object yielded by change_table). (which provides the methods available on the object yielded by create_table) (which provides the methods available in the change, up and down methods),ĪctiveRecord::ConnectionAdapters::TableDefinition execute ( "UPDATE products SET price = 'free' WHERE 1=1" ) Copyįor more details and examples of individual methods, check the API documentation.ĪctiveRecord::ConnectionAdapters::SchemaStatements Representing the number of digits after the decimal point.
Note that if youĪre using a dynamic value (such as a date), the default will only be calculated default Allows to set a default value on the column.collation Specifies the collation for a string or text column.3.5 Column ModifiersĬolumn modifiers can be applied when creating or changing a column: You could also write the above change_column_default migration asĬhange_column_default :products, :approved, false, but unlike the previousĮxample, this would make your migration irreversible. Of course, calculating timestamps is no fun, so Active Record provides a Should be run and in what order, so if you're copying a migration from anotherĪpplication or generate a file yourself, be aware of its position in the order. Rails uses this timestamp to determine which migration For exampleĢ0080906120000_create_products.rb should define class CreateProducts andĢ0080906120001_add_details_to_products.rb should defineĪddDetailsToProducts. Should match the latter part of the file name. The name of the migration class (CamelCased version) Identifying the migration followed by an underscore followed by the name YYYYMMDDHHMMSS_create_products.rb, that is to say a UTC timestamp Migrations are stored as files in the db/migrate directory, one for each change :price, :integer end end end Copy 2 Creating a Migration 2.1 Creating a Standalone Migration
change :price, :string end end def down change_table :products do | t | t. You will have to rollback the changes that were made by hand.Ĭlass ChangeProductsPrice < ActiveRecord :: Migration def up change_table :products do | t | t. Then when a migration fails the parts of it that succeeded will not be rolledīack. On databases that support transactions with statements that change the schema, This migration back, it will remove the table. Active Record knows how to reverse this migration as well: if we roll Note that we define the change that we want to happen moving forward in time.īefore this migration is run, there will be no table. These special columns are automatically managed by Active Record The timestamps macro adds two columns, created_at and Will also be added implicitly, as it's the default primary key for all Active Name and a text column called description. This migration adds a table called products with a string column called Class CreateProducts < ActiveRecord :: Migration def change create_table :products do | t | t.
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