Merge branch 'master' of github.com:lifo/docrails

2022-11-09 12:12:34 -05:00 · 2011-12-04 23:56:46 +05:30 · 2011-12-04 23:56:46 +05:30 · 3134b467f0
commit 3134b467f0
parent 91a3e92cc2 69341d3686
2 changed files with 415 additions and 151 deletions
--- a/railties/guides/source/layouts_and_rendering.textile
+++ b/railties/guides/source/layouts_and_rendering.textile
@ -671,19 +671,33 @@ There are three tag options available for the +auto_discovery_link_tag+:
 h5. Linking to JavaScript Files with the +javascript_include_tag+
-The +javascript_include_tag+ helper returns an HTML +script+ tag for each source provided. Rails looks in +public/javascripts+ for these files by default, but you can specify a full path relative to the document root, or a URL, if you prefer. For example, to include +public/javascripts/main.js+:
+The +javascript_include_tag+ helper returns an HTML +script+ tag for each source provided.
 If you are using Rails with the "Asset Pipeline":http://guides.rubyonrails.org/asset_pipeline.html enabled, this helper will generate a link to +/assets/javascripts/+ rather than +public/javascripts+ which was used in earlier versions of Rails. This link is then served by the Sprockets gem, which was introduced in Rails 3.1.
 A JavaScript file within a Rails application or Rails engine goes in one of three locations: +app/assets+, +lib/assets+ or +vendor/assets+. These locations are explained in detail in the "Asset Organisation section in the Asset Pipeline Guide":http://guides.rubyonrails.org/asset_pipeline.html#asset-organization
 You can specify a full path relative to the document root, or a URL, if you prefer. For example, to link to a JavaScript file that is inside a directory called +javascripts+ inside of one of +app/assets+, +lib/assets+ or +vendor/assets+, you would do this:
 <erb>
 <%= javascript_include_tag "main" %>
 </erb>
-To include +public/javascripts/main.js+ and +public/javascripts/columns.js+:
+Rails will then output a +script+ tag such as this:
 <html>
 <script src='/assets/main.js' type="text/javascript"></script>
 </html>
 The request to this asset is then served by the Sprockets gem.
 To include multiple files such as +app/assets/javascripts/main.js+ and +app/assets/javascripts/columns.js+ at the same time:
 <erb>
 <%= javascript_include_tag "main", "columns" %>
 </erb>
-To include +public/javascripts/main.js+ and +public/photos/columns.js+:
+To include +app/assets/javascripts/main.js+ and +app/assets/javascripts/photos/columns.js+:
 <erb>
 <%= javascript_include_tag "main", "/photos/columns" %>
@ -701,15 +715,38 @@ If the application does not use the asset pipeline, the +:defaults+ option loads
 <%= javascript_include_tag :defaults %>
 </erb>
-And you can in any case override the expansion in <tt>config/application.rb</tt>:
+Outputting +script+ tags such as this:
 <html>
 <script src="/javascripts/jquery.js" type="text/javascript"></script>
 <script src="/javascripts/jquery_ujs.js" type="text/javascript"></script>
 </html>
 These two files for jQuery, +jquery.js+ and +jquery_ujs.js+ must be placed inside +public/javascripts+ if the application doesn't use the asset pipeline. These files can be downloaded from the "jquery-rails repository on GitHub":https://github.com/indirect/jquery-rails/tree/master/vendor/assets/javascripts
 WARNING: If you are using the Asset Pipeline, this tag will render a +script+ tag for an asset called +defaults.js+, which would not exist in your application unless you've explicitly defined it to be.
 And you can in any case override the +:defaults+ expansion in <tt>config/application.rb</tt>:
 <ruby>
 config.action_view.javascript_expansions[:defaults] = %w(foo.js bar.js)
 </ruby>
 You can also define new defaults:
 <ruby>
 config.action_view.javascript_expansions[:projects] = %w(projects.js tickets.js)
 </ruby>
 And use them by referencing them exactly like +:defaults+:
 <erb>
 <%= javascript_include_tag :projects %>
 </erb>
 When using <tt>:defaults</tt>, if an <tt>application.js</tt> file exists in <tt>public/javascripts</tt> it will be included as well at then end.
-Also, the +:all+ option loads every JavaScript file in +public/javascripts+:
+Also, if the Asset Pipeline is disabled, the +:all+ expansion loads every JavaScript file in +public/javascripts+:
 <erb>
 <%= javascript_include_tag :all %>
--- a/railties/guides/source/migrations.textile
+++ b/railties/guides/source/migrations.textile
@ -1,12 +1,24 @@
 h2. Migrations
-Migrations are a convenient way for you to alter your database in a structured and organized manner. You could edit fragments of SQL by hand but you would then be responsible for telling other developers that they need to go and run them. You'd also have to keep track of which changes need to be run against the production machines next time you deploy.
+Migrations are a convenient way for you to alter your database in a structured
 and organized manner. You could edit fragments of SQL by hand but you would then
 be responsible for telling other developers that they need to go and run them.
 You'd also have to keep track of which changes need to be run against the
 production machines next time you deploy.
-Active Record tracks which migrations have already been run so all you have to do is update your source and run +rake db:migrate+. Active Record will work out which migrations should be run. It will also update your +db/schema.rb+ file to match the structure of your database.
+Active Record tracks which migrations have already been run so all you have to
 do is update your source and run +rake db:migrate+. Active Record will work out
 which migrations should be run. It will also update your +db/schema.rb+ file to
 match the structure of your database.
-Migrations also allow you to describe these transformations using Ruby. The great thing about this is that (like most of Active Record's functionality) it is database independent: you don't need to worry about the precise syntax of +CREATE TABLE+ any more than you worry about variations on +SELECT *+ (you can drop down to raw SQL for database specific features). For example you could use SQLite3 in development, but MySQL in production.
+Migrations also allow you to describe these transformations using Ruby. The
 great thing about this is that (like most of Active Record's functionality) it
 is database independent: you don't need to worry about the precise syntax of
 +CREATE TABLE+ any more than you worry about variations on +SELECT *+ (you can
 drop down to raw SQL for database specific features). For example you could use
 SQLite3 in development, but MySQL in production.
-You'll learn all about migrations including:
+In this guide, you'll learn all about migrations including:
 * The generators you can use to create them
 * The methods Active Record provides to manipulate your database
@ -17,7 +29,8 @@ endprologue.
 h3. Anatomy of a Migration
-Before we dive into the details of a migration, here are a few examples of the sorts of things you can do:
+Before we dive into the details of a migration, here are a few examples of the
 sorts of things you can do:
 <ruby>
 class CreateProducts < ActiveRecord::Migration
@ -36,9 +49,15 @@ class CreateProducts < ActiveRecord::Migration
 end
 </ruby>
-This migration adds a table called +products+ with a string column called +name+ and a text column called +description+. A primary key column called +id+ will also be added, however since this is the default we do not need to ask for this. The timestamp columns +created_at+ and +updated_at+ which Active Record populates automatically will also be added. Reversing this migration is as simple as dropping the table.
+This migration adds a table called +products+ with a string column called +name+
 and a text column called +description+. A primary key column called +id+ will
 also be added, however since this is the default we do not need to ask for this.
 The timestamp columns +created_at+ and +updated_at+ which Active Record
 populates automatically will also be added. Reversing this migration is as
 simple as dropping the table.
-Migrations are not limited to changing the schema. You can also use them to fix bad data in the database or populate new fields:
+Migrations are not limited to changing the schema. You can also use them to fix
 bad data in the database or populate new fields:
 <ruby>
 class AddReceiveNewsletterToUsers < ActiveRecord::Migration
@ -55,12 +74,18 @@ class AddReceiveNewsletterToUsers < ActiveRecord::Migration
 end
 </ruby>
-NOTE: Some "caveats":#using-models-in-your-migrations apply to using models in your migrations.
+NOTE: Some "caveats":#using-models-in-your-migrations apply to using models in
 your migrations.
-This migration adds a +receive_newsletter+ column to the +users+ table. We want it to default to +false+ for new users, but existing users are considered
+This migration adds a +receive_newsletter+ column to the +users+ table. We want
-to have already opted in, so we use the User model to set the flag to +true+ for existing users.
+it to default to +false+ for new users, but existing users are considered to
 have already opted in, so we use the User model to set the flag to +true+ for
 existing users.
-Rails 3.1 makes migrations smarter by providing a new <tt>change</tt> method. This method is preferred for writing constructive migrations (adding columns or tables). The migration knows how to migrate your database and reverse it when the migration is rolled back without the need to write a separate +down+ method.
+Rails 3.1 makes migrations smarter by providing a new <tt>change</tt> method.
 This method is preferred for writing constructive migrations (adding columns or
 tables). The migration knows how to migrate your database and reverse it when
 the migration is rolled back without the need to write a separate +down+ method.
 <ruby>
 class CreateProducts < ActiveRecord::Migration
@ -77,64 +102,111 @@ end
 h4. Migrations are Classes
-A migration is a subclass of <tt>ActiveRecord::Migration</tt> that implements two methods: +up+ (perform the required transformations) and +down+ (revert them).
+A migration is a subclass of <tt>ActiveRecord::Migration</tt> that implements
 two methods: +up+ (perform the required transformations) and +down+ (revert
 them).
-Active Record provides methods that perform common data definition tasks in a database independent way (you'll read about them in detail later):
+Active Record provides methods that perform common data definition tasks in a
 database independent way (you'll read about them in detail later):
 * +create_table+
 * +change_table+
 * +drop_table+
 * +add_column+
 * +change_column+
 * +rename_column+
 * +remove_column+
 * +add_index+
 * +change_column+
 * +change_table+
 * +create_table+
 * +drop_table+
 * +remove_column+
 * +remove_index+
 * +rename_column+
-If you need to perform tasks specific to your database (for example create a "foreign key":#active-record-and-referential-integrity constraint) then the +execute+ method allows you to execute arbitrary SQL. A migration is just a regular Ruby class so you're not limited to these functions. For example after adding a column you could write code to set the value of that column for existing records (if necessary using your models).
+If you need to perform tasks specific to your database (for example create a
 "foreign key":#active-record-and-referential-integrity constraint) then the
 +execute+ method allows you to execute arbitrary SQL. A migration is just a
 regular Ruby class so you're not limited to these functions. For example after
 adding a column you could write code to set the value of that column for
 existing records (if necessary using your models).
-On databases that support transactions with statements that change the schema (such as PostgreSQL or SQLite3), migrations are wrapped in a transaction. If the database does not support this (for example MySQL) then when a migration fails the parts of it that succeeded will not be rolled back. You will have to unpick the changes that were made by hand.
+On databases that support transactions with statements that change the schema
 (such as PostgreSQL or SQLite3), migrations are wrapped in a transaction. If the
 database does not support this (for example MySQL) then when a migration fails
 the parts of it that succeeded will not be rolled back. You will have to rollback
 the changes that were made by hand.
 h4. What's in a Name
-Migrations are stored in files in +db/migrate+, one for each migration class. The name of the file is of the form +YYYYMMDDHHMMSS_create_products.rb+, that is to say a UTC timestamp identifying the migration followed by an underscore followed by the name of the migration. The name of the migration class (CamelCased version) should match the latter part of the file name. For example +20080906120000_create_products.rb+ should define class +CreateProducts+ and +20080906120001_add_details_to_products.rb+ should define +AddDetailsToProducts+. If you do feel the need to change the file name then you <em>have to</em> update the name of the class inside or Rails will complain about a missing class.
+Migrations are stored as files in the +db/migrate+ directory, one for each
 migration class. The name of the file is of the form
 +YYYYMMDDHHMMSS_create_products.rb+, that is to say a UTC timestamp
 identifying the migration followed by an underscore followed by the name
 of the migration. The name of the migration class (CamelCased version)
 should match the latter part of the file name. For example
 +20080906120000_create_products.rb+ should define class +CreateProducts+ and
 +20080906120001_add_details_to_products.rb+ should define
 +AddDetailsToProducts+. If you do feel the need to change the file name then you
 <em>have to</em> update the name of the class inside or Rails will complain
 about a missing class.
-Internally Rails only uses the migration's number (the timestamp) to identify them. Prior to Rails 2.1 the migration number started at 1 and was incremented each time a migration was generated. With multiple developers it was easy for these to clash requiring you to rollback migrations and renumber them. With Rails 2.1 this is largely avoided by using the creation time of the migration to identify them. You can revert to the old numbering scheme by adding the following line to +config/application.rb+.
+Internally Rails only uses the migration's number (the timestamp) to identify
 them. Prior to Rails 2.1 the migration number started at 1 and was incremented
 each time a migration was generated. With multiple developers it was easy for
 these to clash requiring you to rollback migrations and renumber them. With
 Rails 2.1+ this is largely avoided by using the creation time of the migration
 to identify them. You can revert to the old numbering scheme by adding the
 following line to +config/application.rb+.
 <ruby>
 config.active_record.timestamped_migrations = false
 </ruby>
-The combination of timestamps and recording which migrations have been run allows Rails to handle common situations that occur with multiple developers.
+The combination of timestamps and recording which migrations have been run
 allows Rails to handle common situations that occur with multiple developers.
-For example Alice adds migrations +20080906120000+ and +20080906123000+ and Bob adds +20080906124500+ and runs it. Alice finishes her changes and checks in her migrations and Bob pulls down the latest changes. Rails knows that it has not run Alice's two migrations so +rake db:migrate+ would run them (even though Bob's migration with a later timestamp has been run), and similarly migrating down would not run their +down+ methods.
+For example Alice adds migrations +20080906120000+ and +20080906123000+ and Bob
 adds +20080906124500+ and runs it. Alice finishes her changes and checks in her
 migrations and Bob pulls down the latest changes. When Bob runs +rake db:migrate+,
 Rails knows that it has not run Alice's two migrations so it executes the +up+ method for each migration.
-Of course this is no substitution for communication within the team. For example, if Alice's migration removed a table that Bob's migration assumed to exist, then trouble would certainly strike.
+Of course this is no substitution for communication within the team. For
 example, if Alice's migration removed a table that Bob's migration assumed to
 exist, then trouble would certainly strike.
 h4. Changing Migrations
-Occasionally you will make a mistake when writing a migration. If you have already run the migration then you cannot just edit the migration and run the migration again: Rails thinks it has already run the migration and so will do nothing when you run +rake db:migrate+. You must rollback the migration (for example with +rake db:rollback+), edit your migration and then run +rake db:migrate+ to run the corrected version.
+Occasionally you will make a mistake when writing a migration. If you have
 already run the migration then you cannot just edit the migration and run the
 migration again: Rails thinks it has already run the migration and so will do
 nothing when you run +rake db:migrate+. You must rollback the migration (for
 example with +rake db:rollback+), edit your migration and then run +rake db:migrate+ to run the corrected version.
-In general editing existing migrations is not a good idea: you will be creating extra work for yourself and your co-workers and cause major headaches if the existing version of the migration has already been run on production machines. Instead, you should write a new migration that performs the changes you require. Editing a freshly generated migration that has not yet been committed to source control (or, more generally, which has not been propagated beyond your development machine) is relatively harmless.
+In general editing existing migrations is not a good idea: you will be creating
 extra work for yourself and your co-workers and cause major headaches if the
 existing version of the migration has already been run on production machines.
 Instead, you should write a new migration that performs the changes you require.
 Editing a freshly generated migration that has not yet been committed to source
 control (or, more generally, which has not been propagated beyond your
 development machine) is relatively harmless.
 h4. Supported Types
-Active Record supports the following types:
+Active Record supports the following database column types:
 * +:binary+
 * +:boolean+
 * +:date+
 * +:datetime+
 * +:decimal+
 * +:float+
 * +:integer+
 * +:primary_key+
 * +:string+
 * +:text+
 * +:integer+
 * +:float+
 * +:decimal+
 * +:datetime+
 * +:timestamp+
 * +:time+
-* +:date+
+* +:timestamp+
 * +:binary+
 * +:boolean+
-These will be mapped onto an appropriate underlying database type. For example, with MySQL the type +:string+ is mapped to +VARCHAR(255)+. You can create columns of types not supported by Active Record when using the non-sexy syntax, for example
+These will be mapped onto an appropriate underlying database type. For example,
 with MySQL the type +:string+ is mapped to +VARCHAR(255)+. You can create
 columns of types not supported by Active Record when using the non-sexy syntax,
 for example
 <ruby>
 create_table :products do |t|
@ -148,7 +220,10 @@ h3. Creating a Migration
 h4. Creating a Model
-The model and scaffold generators will create migrations appropriate for adding a new model. This migration will already contain instructions for creating the relevant table. If you tell Rails what columns you want, then statements for adding these columns will also be created. For example, running
+The model and scaffold generators will create migrations appropriate for adding
 a new model. This migration will already contain instructions for creating the
 relevant table. If you tell Rails what columns you want, then statements for
 adding these columns will also be created. For example, running
 <shell>
 $ rails generate model Product name:string description:text
@ -169,12 +244,15 @@ class CreateProducts < ActiveRecord::Migration
 end
 </ruby>
-You can append as many column name/type pairs as you want. By default +t.timestamps+ (which creates the +updated_at+ and +created_at+ columns that
+You can append as many column name/type pairs as you want. By default, the
-are automatically populated by Active Record) will be added for you.
+generated migration will include +t.timestamps+ (which creates the
 +updated_at+ and +created_at+ columns that are automatically populated
 by Active Record).
 h4. Creating a Standalone Migration
-If you are creating migrations for other purposes (for example to add a column to an existing table) then you can use the migration generator:
+If you are creating migrations for other purposes (for example to add a column
 to an existing table) then you can also use the migration generator:
 <shell>
 $ rails generate migration AddPartNumberToProducts
@ -189,7 +267,9 @@ class AddPartNumberToProducts < ActiveRecord::Migration
 end
 </ruby>
-If the migration name is of the form "AddXXXToYYY" or "RemoveXXXFromYYY" and is followed by a list of column names and types then a migration containing the appropriate +add_column+ and +remove_column+ statements will be created.
+If the migration name is of the form "AddXXXToYYY" or "RemoveXXXFromYYY" and is
 followed by a list of column names and types then a migration containing the
 appropriate +add_column+ and +remove_column+ statements will be created.
 <shell>
 $ rails generate migration AddPartNumberToProducts part_number:string
@ -242,17 +322,23 @@ class AddDetailsToProducts < ActiveRecord::Migration
 end
 </ruby>
-As always, what has been generated for you is just a starting point. You can add or remove from it as you see fit.
+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.
-NOTE: The generated migration file for destructive migrations will still be old-style using the +up+ and +down+ methods. This is because Rails doesn't know the original data types defined when you made the original changes.
+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.
 h3. Writing a Migration
-Once you have created your migration using one of the generators it's time to get to work!
+Once you have created your migration using one of the generators it's time to
 get to work!
 h4. Creating a Table
-Migration method +create_table+ will be one of your workhorses. A typical use would be
+Migration method +create_table+ will be one of your workhorses. A typical use
 would be
 <ruby>
 create_table :products do |t|
@ -260,9 +346,11 @@ create_table :products do |t|
 end
 </ruby>
-which creates a +products+ table with a column called +name+ (and as discussed below, an implicit +id+ column).
+which creates a +products+ table with a column called +name+ (and as discussed
 below, an implicit +id+ column).
-The object yielded to the block allows you to create columns on the table. There are two ways of doing it. The first (traditional) form looks like
+The object yielded to the block allows you to create columns on the table. There
 are two ways of doing it. The first (traditional) form looks like
 <ruby>
 create_table :products do |t|
@ -270,7 +358,9 @@ create_table :products do |t|
 end
 </ruby>
-The second form, the so called "sexy" migration, drops the somewhat redundant +column+ method. Instead, the +string+, +integer+, etc. methods create a column of that type. Subsequent parameters are the same.
+The second form, the so called "sexy" migration, drops the somewhat redundant
 +column+ method. Instead, the +string+, +integer+, etc. methods create a column
 of that type. Subsequent parameters are the same.
 <ruby>
 create_table :products do |t|
@ -278,7 +368,12 @@ create_table :products do |t|
 end
 </ruby>
-By default, +create_table+ will create a primary key called +id+. You can change the name of the primary key with the +:primary_key+ option (don't forget to update the corresponding model) or, if you don't want a primary key at all (for example for a HABTM join table), you can pass the option +:id => false+. If you need to pass database specific options you can place an SQL fragment in the +:options+ option. For example,
+By default, +create_table+ will create a primary key called +id+. You can change
 the name of the primary key with the +:primary_key+ option (don't forget to
 update the corresponding model) or, if you don't want a primary key at all (for
 example for a HABTM join table), you can pass the option +:id => false+. If you
 need to pass database specific options you can place an SQL fragment in the
 +:options+ option. For example,
 <ruby>
 create_table :products, :options => "ENGINE=BLACKHOLE" do |t|
@ -286,11 +381,14 @@ create_table :products, :options => "ENGINE=BLACKHOLE" do |t|
 end
 </ruby>
-will append +ENGINE=BLACKHOLE+ to the SQL statement used to create the table (when using MySQL, the default is +ENGINE=InnoDB+).
+will append +ENGINE=BLACKHOLE+ to the SQL statement used to create the table
 (when using MySQL, the default is +ENGINE=InnoDB+).
 h4. Changing Tables
-A close cousin of +create_table+ is +change_table+, used for changing existing tables. It is used in a similar fashion to +create_table+ but the object yielded to the block knows more tricks. For example
+A close cousin of +create_table+ is +change_table+, used for changing existing
 tables. It is used in a similar fashion to +create_table+ but the object yielded
 to the block knows more tricks. For example
 <ruby>
 change_table :products do |t|
@ -301,28 +399,23 @@ change_table :products do |t|
 end
 </ruby>
-removes the +description+ and +name+ columns, creates a +part_number+ column and adds an index on it. Finally it renames the +upccode+ column. This is the same as doing
+removes the +description+ and +name+ columns, creates a +part_number+ string
-
+column and adds an index on it. Finally it renames the +upccode+ column.
 <ruby>
 remove_column :products, :description
 remove_column :products, :name
 add_column :products, :part_number, :string
 add_index :products, :part_number
 rename_column :products, :upccode, :upc_code
 </ruby>
 You don't have to keep repeating the table name and it groups all the statements related to modifying one particular table. The individual transformation names are also shorter, for example +remove_column+ becomes just +remove+ and +add_index+ becomes just +index+.
 h4. Special Helpers
-Active Record provides some shortcuts for common functionality. It is for example very common to add both the +created_at+ and +updated_at+ columns and so there is a method that does exactly that:
+Active Record provides some shortcuts for common functionality. It is for
 example very common to add both the +created_at+ and +updated_at+ columns and so
 there is a method that does exactly that:
 <ruby>
 create_table :products do |t|
  t.timestamps
 end
 </ruby>
-will create a new products table with those two columns (plus the +id+ column) whereas
+
 will create a new products table with those two columns (plus the +id+ column)
 whereas
 <ruby>
 change_table :products do |t|
@ -331,7 +424,8 @@ end
 </ruby>
 adds those columns to an existing table.
-The other helper is called +references+ (also available as +belongs_to+). In its simplest form it just adds some readability
+Another helper is called +references+ (also available as +belongs_to+). In its
 simplest form it just adds some readability.
 <ruby>
 create_table :products do |t|
@ -339,24 +433,42 @@ create_table :products do |t|
 end
 </ruby>
-will create a +category_id+ column of the appropriate type. Note that you pass the model name, not the column name. Active Record adds the +_id+ for you. If you have polymorphic +belongs_to+ associations then +references+ will add both of the columns required:
+will create a +category_id+ column of the appropriate type. Note that you pass
 the model name, not the column name. Active Record adds the +_id+ for you. If
 you have polymorphic +belongs_to+ associations then +references+ will add both
 of the columns required:
 <ruby>
 create_table :products do |t|
  t.references :attachment, :polymorphic => {:default => 'Photo'}
 end
 </ruby>
 will add an +attachment_id+ column and a string +attachment_type+ column with a default value of 'Photo'.
-NOTE: The +references+ helper does not actually create foreign key constraints for you. You will need to use +execute+ or a plugin that adds "foreign key support":#active-record-and-referential-integrity.
+will add an +attachment_id+ column and a string +attachment_type+ column with
 a default value of 'Photo'.
-If the helpers provided by Active Record aren't enough you can use the +execute+ method to execute arbitrary SQL.
+NOTE: The +references+ helper does not actually create foreign key constraints
 for you. You will need to use +execute+ or a plugin that adds "foreign key
 support":#active-record-and-referential-integrity.
-For more details and examples of individual methods, check the API documentation, in particular the documentation for "<tt>ActiveRecord::ConnectionAdapters::SchemaStatements</tt>":http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html (which provides the methods available in the +up+ and +down+ methods), "<tt>ActiveRecord::ConnectionAdapters::TableDefinition</tt>":http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/TableDefinition.html (which provides the methods available on the object yielded by +create_table+) and "<tt>ActiveRecord::ConnectionAdapters::Table</tt>":http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/Table.html (which provides the methods available on the object yielded by +change_table+).
+If the helpers provided by Active Record aren't enough you can use the +execute+
 method to execute arbitrary SQL.
-h4. Writing Your +change+ Method
+For more details and examples of individual methods, check the API documentation,
 in particular the documentation for
 "<tt>ActiveRecord::ConnectionAdapters::SchemaStatements</tt>":http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html
 (which provides the methods available in the +up+ and +down+ methods),
 "<tt>ActiveRecord::ConnectionAdapters::TableDefinition</tt>":http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/TableDefinition.html
 (which provides the methods available on the object yielded by +create_table+)
 and
 "<tt>ActiveRecord::ConnectionAdapters::Table</tt>":http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/Table.html
 (which provides the methods available on the object yielded by +change_table+).
-The +change+ method removes the need to write both +up+ and +down+ methods in those cases that Rails know how to revert the changes automatically. Currently, the +change+ method supports only these migration definitions:
+h4. Using the +change+ Method
 The +change+ method removes the need to write both +up+ and +down+ methods in
 those cases that Rails know how to revert the changes automatically. Currently,
 the +change+ method supports only these migration definitions:
 * +add_column+
 * +add_index+
@ -367,15 +479,20 @@ The +change+ method removes the need to write both +up+ and +down+ methods in th
 * +rename_index+
 * +rename_table+
-If you're going to use other methods, you'll have to write the +up+ and +down+ methods normally.
+If you're going to need to use any other methods, you'll have to write the
 +up+ and +down+ methods instead of using the +change+ method.
-h4. Writing Your +down+ Method
+h4. Using the +up+/+down+ Methods
-The +down+ method of your migration should revert the transformations done by the +up+ method. In other words, the database schema should be unchanged if you do an +up+ followed by a +down+. For example, if you create a table in the +up+ method, you should drop it in the +down+ method. It is wise to reverse the transformations in precisely the reverse order they were made in the +up+ method. For example,
+The +down+ method of your migration should revert the transformations done by
 the +up+ method. In other words, the database schema should be unchanged if you
 do an +up+ followed by a +down+. For example, if you create a table in the +up+
 method, you should drop it in the +down+ method. It is wise to reverse the
 transformations in precisely the reverse order they were made in the +up+
 method. For example,
 <ruby>
 class ExampleMigration < ActiveRecord::Migration
  def up
    create_table :products do |t|
      t.references :category
@ -387,47 +504,69 @@ class ExampleMigration < ActiveRecord::Migration
        FOREIGN KEY (category_id)
        REFERENCES categories(id)
    SQL
    add_column :users, :home_page_url, :string
    rename_column :users, :email, :email_address
  end
  def down
    rename_column :users, :email_address, :email
    remove_column :users, :home_page_url
-    execute "ALTER TABLE products DROP FOREIGN KEY fk_products_categories"
+    execute <<-SQL
      ALTER TABLE products
        DROP FOREIGN KEY fk_products_categories
    SQL
    drop_table :products
  end
 end
 </ruby>
-Sometimes your migration will do something which is just plain irreversible; for example, it might destroy some data. In such cases, you can raise +ActiveRecord::IrreversibleMigration+ from your +down+ method. If someone tries to revert your migration, an error message will be displayed saying that it can't be done.
+Sometimes your migration will do something which is just plain irreversible; for
 example, it might destroy some data. In such cases, you can raise
 +ActiveRecord::IrreversibleMigration+ from your +down+ method. If someone tries
 to revert your migration, an error message will be displayed saying that it
 can't be done.
 h3. Running Migrations
-Rails provides a set of rake tasks to work with migrations which boil down to running certain sets of migrations. The very first migration related rake task you will use will probably be +db:migrate+. In its most basic form it just runs the +up+ method for all the migrations that have not yet been run. If there are no such migrations, it exits.
+Rails provides a set of rake tasks to work with migrations which boil down to
 running certain sets of migrations.
-Note that running the +db:migrate+ also invokes the +db:schema:dump+ task, which will update your db/schema.rb file to match the structure of your database.
+The very first migration related rake task you will use will probably be
 +rake db:migrate+. In its most basic form it just runs the +up+ or +change+
 method for all the migrations that have not yet been run. If there are
 no such migrations, it exits. It will run these migrations in order based
 on the date of the migration.
-If you specify a target version, Active Record will run the required migrations (up or down) until it has reached the specified version. The
+Note that running the +db:migrate+ also invokes the +db:schema:dump+ task, which
-version is the numerical prefix on the migration's filename. For example, to migrate to version 20080906120000 run
+will update your db/schema.rb file to match the structure of your database.
 If you specify a target version, Active Record will run the required migrations
 (up or down or change) until it has reached the specified version. The version
 is the numerical prefix on the migration's filename. For example, to migrate
 to version 20080906120000 run
 <shell>
 $ rake db:migrate VERSION=20080906120000
 </shell>
-If version 20080906120000 is greater than the current version (i.e., it is migrating upwards), this will run the +up+ method on all migrations up to and including 20080906120000. If migrating downwards, this will run the +down+ method on all the migrations down to, but not including, 20080906120000.
+If version 20080906120000 is greater than the current version (i.e., it is
 migrating upwards), this will run the +up+ method on all migrations up to and
 including 20080906120000, and will not execute any later migrations. If
 migrating downwards, this will run the +down+ method on all the migrations
 down to, but not including, 20080906120000.
 h4. Rolling Back
-A common task is to rollback the last migration, for example if you made a mistake in it and wish to correct it. Rather than tracking down the version number associated with the previous migration you can run
+A common task is to rollback the last migration, for example if you made a
 mistake in it and wish to correct it. Rather than tracking down the version
 number associated with the previous migration you can run
 <shell>
 $ rake db:rollback
 </shell>
-This will run the +down+ method from the latest migration. If you need to undo several migrations you can provide a +STEP+ parameter:
+This will run the +down+ method from the latest migration. If you need to undo
 several migrations you can provide a +STEP+ parameter:
 <shell>
 $ rake db:rollback STEP=3
@ -435,46 +574,65 @@ $ rake db:rollback STEP=3
 will run the +down+ method from the last 3 migrations.
-The +db:migrate:redo+ task is a shortcut for doing a rollback and then migrating back up again. As with the +db:rollback+ task, you can use the +STEP+ parameter if you need to go more than one version back, for example
+The +db:migrate:redo+ task is a shortcut for doing a rollback and then migrating
 back up again. As with the +db:rollback+ task, you can use the +STEP+ parameter
 if you need to go more than one version back, for example
 <shell>
 $ rake db:migrate:redo STEP=3
 </shell>
-Neither of these Rake tasks do anything you could not do with +db:migrate+. They are simply more convenient, since you do not need to explicitly specify the version to migrate to.
+Neither of these Rake tasks do anything you could not do with +db:migrate+. They
 are simply more convenient, since you do not need to explicitly specify the
 version to migrate to.
-Lastly, the +db:reset+ task will drop the database, recreate it and load the current schema into it.
+h4. Resetting the database
-NOTE: This is not the same as running all the migrations - see the section on "schema.rb":#schema-dumping-and-you.
+The +rake db:reset+ task will drop the database, recreate it and load the
 current schema into it.
-h4. Being Specific
+NOTE: This is not the same as running all the migrations - see the section on
 "schema.rb":#schema-dumping-and-you.
-If you need to run a specific migration up or down, the +db:migrate:up+ and +db:migrate:down+ tasks will do that. Just specify the appropriate version and the corresponding migration will have its +up+ or +down+ method invoked, for example,
+h4. Running specific migrations
 If you need to run a specific migration up or down, the +db:migrate:up+ and
 +db:migrate:down+ tasks will do that. Just specify the appropriate version and
 the corresponding migration will have its +up+ or +down+ method invoked, for
 example,
 <shell>
 $ rake db:migrate:up VERSION=20080906120000
 </shell>
-will run the +up+ method from the 20080906120000 migration. These tasks check whether the migration has already run, so for example +db:migrate:up VERSION=20080906120000+ will do nothing if Active Record believes that 20080906120000 has already been run.
+will run the +up+ method from the 20080906120000 migration. These tasks still
 check whether the migration has already run, so for example +db:migrate:up
 VERSION=20080906120000+ will do nothing if Active Record believes that
 20080906120000 has already been run.
-h4. Being Talkative
+h4. Changing the output of running migrations
-By default migrations tell you exactly what they're doing and how long it took. A migration creating a table and adding an index might produce output like this
+By default migrations tell you exactly what they're doing and how long it took.
 A migration creating a table and adding an index might produce output like this
 <shell>
-20080906170109 CreateProducts: migrating
+==  CreateProducts: migrating =================================================
 -- create_table(:products)
-   -> 0.0021s
+   -> 0.0028s
-- add_index(:products, :name)
+==  CreateProducts: migrated (0.0028s) ========================================
   -> 0.0026s
 20080906170109 CreateProducts: migrated (0.0059s)
 </shell>
-Several methods are provided that allow you to control all this:
+Several methods are provided in migrations that allow you to control all this:
-* +suppress_messages+ takes a block as an argument and suppresses any output generated by the block.
+|_.Method             |_.Purpose|
-* +say+ takes a message argument and outputs it as is. A second boolean argument can be passed to specify whether to indent or not.
+|suppress_messages    |Takes a block as an argument and suppresses any output
-* +say_with_time+ outputs text along with how long it took to run its block. If the block returns an integer it assumes it is the number of rows affected.
+                       generated by the block.|
 |say                  |Takes a message argument and outputs it as is. A second
                       boolean argument can be passed to specify whether to
                       indent or not.|
 |say_with_time        |Outputs text along with how long it took to run its
                       block. If the block returns an integer it assumes it
                       is the number of rows affected.|
 For example, this migration
@ -502,37 +660,46 @@ end
 generates the following output
 <shell>
-20080906170109 CreateProducts: migrating
+==  CreateProducts: migrating =================================================
-  Created a table
+-- Created a table
   -> and an index!
-  Waiting for a while
+-- Waiting for a while
-   -> 10.0001s
+   -> 10.0013s
   -> 250 rows
-20080906170109 CreateProducts: migrated (10.0097s)
+==  CreateProducts: migrated (10.0054s) =======================================
 </shell>
-If you just want Active Record to shut up, then running +rake db:migrate VERBOSE=false+ will suppress all output.
+If you want Active Record to not output anything, then running +rake db:migrate
 VERBOSE=false+ will suppress all output.
 h3. Using Models in Your Migrations
-When creating or updating data in a migration it is often tempting to use one of your models. After all, they exist to provide easy access to the underlying data. This can be done, but some caution should be observed.
+When creating or updating data in a migration it is often tempting to use one of
 your models. After all, they exist to provide easy access to the underlying
 data. This can be done, but some caution should be observed.
-For example, problems occur when the model uses database columns which are (1) not currently in the database and (2) will be created by this or a subsequent migration.
+For example, problems occur when the model uses database columns which are (1)
 not currently in the database and (2) will be created by this or a subsequent
 migration.
-Consider this example, where Alice and Bob are working on the same code base which contains a +Product+ model:
+Consider this example, where Alice and Bob are working on the same code base
 which contains a +Product+ model:
 Bob goes on vacation.
-Alice creates a migration for the +products+ table which adds a new column and initializes it.
+Alice creates a migration for the +products+ table which adds a new column and
-She also adds a validation to the +Product+ model for the new column.
+initializes it.  She also adds a validation to the +Product+ model for the new
 column.
 <ruby>
 # db/migrate/20100513121110_add_flag_to_product.rb
 class AddFlagToProduct < ActiveRecord::Migration
  def change
-    add_column :products, :flag, :int
+    add_column :products, :flag, :boolean
-    Product.all.each { |f| f.update_attributes!(:flag => 'false') }
+    Product.all.each do |product|
      product.update_attributes!(:flag => 'false')
    end
  end
 end
 </ruby>
@ -545,7 +712,9 @@ class Product < ActiveRecord::Base
 end
 </ruby>
-Alice adds a second migration which adds and initializes another column to the +products+ table and also adds a validation to the +Product+ model for the new column.
+Alice adds a second migration which adds and initializes another column to the
 +products+ table and also adds a validation to the +Product+ model for the new
 column.
 <ruby>
 # db/migrate/20100515121110_add_fuzz_to_product.rb
@ -553,7 +722,9 @@ Alice adds a second migration which adds and initializes another column to the +
 class AddFuzzToProduct < ActiveRecord::Migration
  def change
    add_column :products, :fuzz, :string
-    Product.all.each { |f| f.update_attributes! :fuzz => 'fuzzy' }
+    Product.all.each do |product|
      product.update_attributes! :fuzz => 'fuzzy'
    end
  end
 end
 </ruby>
@ -570,10 +741,14 @@ Both migrations work for Alice.
 Bob comes back from vacation and:
-# updates the source - which contains both migrations and the latests version of the Product model.
+# Updates the source - which contains both migrations and the latests version of
-# runs outstanding migrations with +rake db:migrate+, which includes the one that updates the +Product+ model.
+the Product model.
 # Runs outstanding migrations with +rake db:migrate+, which
 includes the one that updates the +Product+ model.
-The migration crashes because when the model attempts to save, it tries to validate the second added column, which is not in the database when the _first_ migration runs:
+The migration crashes because when the model attempts to save, it tries to
 validate the second added column, which is not in the database when the _first_
 migration runs:
 <plain>
 rake aborted!
@ -582,9 +757,12 @@ An error has occurred, this and all later migrations canceled:
 undefined method `fuzz' for #<Product:0x000001049b14a0>
 </plain>
-A fix for this is to create a local model within the migration. This keeps rails from running the validations, so that the migrations run to completion.
+A fix for this is to create a local model within the migration. This keeps rails
 from running the validations, so that the migrations run to completion.
-When using a faux model, it's a good idea to call +Product.reset_column_information+ to refresh the +ActiveRecord+ cache for the +Product+ model prior to updating data in the database.
+When using a faux model, it's a good idea to call
 +Product.reset_column_information+ to refresh the +ActiveRecord+ cache for the
 +Product+ model prior to updating data in the database.
 If Alice had done this instead, there would have been no problem:
@ -596,9 +774,11 @@ class AddFlagToProduct < ActiveRecord::Migration
  end
  def change
-    add_column :products, :flag, :int
+    add_column :products, :flag, :integer
    Product.reset_column_information
-    Product.all.each { |f| f.update_attributes!(:flag => false) }
+    Product.all.each do |product|
      product.update_attributes!(:flag => false)
    end
  end
 end
 </ruby>
@ -609,32 +789,50 @@ end
 class AddFuzzToProduct < ActiveRecord::Migration
  class Product < ActiveRecord::Base
  end
  def change
    add_column :products, :fuzz, :string
    Product.reset_column_information
-    Product.all.each { |f| f.update_attributes! :fuzz => 'fuzzy' }
+    Product.all.each do |product|
      product.update_attributes!(:fuzz => 'fuzzy')
    end
  end
 end
 </ruby>
 h3. Schema Dumping and You
 h4. What are Schema Files for?
-Migrations, mighty as they may be, are not the authoritative source for your database schema. That role falls to either +db/schema.rb+ or an SQL file which Active Record generates by examining the database. They are not designed to be edited, they just represent the current state of the database.
+Migrations, mighty as they may be, are not the authoritative source for your
 database schema. That role falls to either +db/schema.rb+ or an SQL file which
 Active Record generates by examining the database. They are not designed to be
 edited, they just represent the current state of the database.
-There is no need (and it is error prone) to deploy a new instance of an app by replaying the entire migration history. It is much simpler and faster to just load into the database a description of the current schema.
+There is no need (and it is error prone) to deploy a new instance of an app by
 replaying the entire migration history. It is much simpler and faster to just
 load into the database a description of the current schema.
-For example, this is how the test database is created: the current development database is dumped (either to +db/schema.rb+ or +db/development.sql+) and then loaded into the test database.
+For example, this is how the test database is created: the current development
 database is dumped (either to +db/schema.rb+ or +db/development.sql+) and then
 loaded into the test database.
-Schema files are also useful if you want a quick look at what attributes an Active Record object has. This information is not in the model's code and is frequently spread across several migrations, but is summed up in the schema file. The "annotate_models":https://github.com/ctran/annotate_models gem automatically adds and updates comments at the top of each model summarizing the schema if you desire that functionality.
+Schema files are also useful if you want a quick look at what attributes an
 Active Record object has. This information is not in the model's code and is
 frequently spread across several migrations, but the information is nicely
 summed up in the schema file. The
 "annotate_models":https://github.com/ctran/annotate_models gem automatically
 adds and updates comments at the top of each model summarizing the schema if
 you desire that functionality.
 h4. Types of Schema Dumps
-There are two ways to dump the schema. This is set in +config/application.rb+ by the +config.active_record.schema_format+ setting, which may be either +:sql+ or +:ruby+.
+There are two ways to dump the schema. This is set in +config/application.rb+ by
 the +config.active_record.schema_format+ setting, which may be either +:sql+ or
 +:ruby+.
-If +:ruby+ is selected then the schema is stored in +db/schema.rb+. If you look at this file you'll find that it looks an awful lot like one very big migration:
+If +:ruby+ is selected then the schema is stored in +db/schema.rb+. If you look
 at this file you'll find that it looks an awful lot like one very big migration:
 <ruby>
 ActiveRecord::Schema.define(:version => 20080906171750) do
@ -646,28 +844,57 @@ ActiveRecord::Schema.define(:version => 20080906171750) do
  create_table "products", :force => true do |t|
    t.string   "name"
-    t.text     "description"
+    t.text "description"
    t.datetime "created_at"
    t.datetime "updated_at"
-    t.string   "part_number"
+    t.string "part_number"
  end
 end
 </ruby>
-In many ways this is exactly what it is. This file is created by inspecting the database and expressing its structure using +create_table+, +add_index+, and so on. Because this is database-independent, it could be loaded into any database that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases.
+In many ways this is exactly what it is. This file is created by inspecting the
 database and expressing its structure using +create_table+, +add_index+, and so
 on. Because this is database-independent, it could be loaded into any database
 that Active Record supports. This could be very useful if you were to distribute
 an application that is able to run against multiple databases.
-There is however a trade-off: +db/schema.rb+ cannot express database specific items such as foreign key constraints, triggers, or stored procedures. While in a migration you can execute custom SQL statements, the schema dumper cannot reconstitute those statements from the database. If you are using features like this, then you should set the schema format to +:sql+.
+There is however a trade-off: +db/schema.rb+ cannot express database specific
 items such as foreign key constraints, triggers, or stored procedures. While in
 a migration you can execute custom SQL statements, the schema dumper cannot
 reconstitute those statements from the database. If you are using features like
 this, then you should set the schema format to +:sql+.
-Instead of using Active Record's schema dumper, the database's structure will be dumped using a tool specific to the database (via the +db:structure:dump+ Rake task) into +db/structure.sql+. For example, for the PostgreSQL RDBMS, the +pg_dump+ utility is used. For MySQL, this file will contain the output of +SHOW CREATE TABLE+ for the various tables. Loading these schemas is simply a question of executing the SQL statements they contain. By definition, this will create a perfect copy of the database's structure. Using the +:sql+ schema format will, however, prevent loading the schema into a RDBMS other than the one used to create it.
+Instead of using Active Record's schema dumper, the database's structure will be
 dumped using a tool specific to the database (via the +db:structure:dump+ Rake task)
 into +db/structure.sql+. For example, for the PostgreSQL RDBMS, the
 +pg_dump+ utility is used. For MySQL, this file will contain the output of +SHOW
 CREATE TABLE+ for the various tables. Loading these schemas is simply a question
 of executing the SQL statements they contain. By definition, this will create a
 perfect copy of the database's structure. Using the +:sql+ schema format will,
 however, prevent loading the schema into a RDBMS other than the one used to
 create it.
 h4. Schema Dumps and Source Control
-Because schema dumps are the authoritative source for your database schema, it is strongly recommended that you check them into source control.
+Because schema dumps are the authoritative source for your database schema, it
 is strongly recommended that you check them into source control.
 h3. Active Record and Referential Integrity
-The Active Record way claims that intelligence belongs in your models, not in the database. As such, features such as triggers or foreign key constraints, which push some of that intelligence back into the database, are not heavily used.
+The Active Record way claims that intelligence belongs in your models, not in
 the database. As such, features such as triggers or foreign key constraints,
 which push some of that intelligence back into the database, are not heavily
 used.
-Validations such as +validates :foreign_key, :uniqueness => true+ are one way in which models can enforce data integrity. The +:dependent+ option on associations allows models to automatically destroy child objects when the parent is destroyed. Like anything which operates at the application level, these cannot guarantee referential integrity and so some people augment them with foreign key constraints.
+Validations such as +validates :foreign_key, :uniqueness => true+ are one way in
 which models can enforce data integrity. The +:dependent+ option on associations
 allows models to automatically destroy child objects when the parent is
 destroyed. Like anything which operates at the application level, these cannot
 guarantee referential integrity and so some people augment them with foreign key
 constraints in the database.
-Although Active Record does not provide any tools for working directly with such features, the +execute+ method can be used to execute arbitrary SQL. You could also use some plugin like "foreigner":https://github.com/matthuhiggins/foreigner which add foreign key support to Active Record (including support for dumping foreign keys in +db/schema.rb+).
+Although Active Record does not provide any tools for working directly with such
 features, the +execute+ method can be used to execute arbitrary SQL. You could
 also use some plugin like "foreigner":https://github.com/matthuhiggins/foreigner
 which add foreign key support to Active Record (including support for dumping
 foreign keys in +db/schema.rb+).