439 lines
11 KiB
Markdown
439 lines
11 KiB
Markdown
Active Record and PostgreSQL
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============================
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This guide covers PostgreSQL specific usage of Active Record.
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After reading this guide, you will know:
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* How to use PostgreSQL's datatypes.
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* How to use UUID primary keys.
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* How to implement full text search with PostgreSQL.
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* How to back your Active Record models with database views.
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--------------------------------------------------------------------------------
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In order to use the PostgreSQL adapter you need to have at least version 8.2
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installed. Older versions are not supported.
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To get started with PostgreSQL have a look at the
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[configuring Rails guide](configuring.html#configuring-a-postgresql-database).
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It describes how to properly setup Active Record for PostgreSQL.
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Datatypes
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---------
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PostgreSQL offers a number of specific datatypes. Following is a list of types,
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that are supported by the PostgreSQL adapter.
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### Bytea
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-binary.html)
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* [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-binarystring.html)
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```ruby
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# db/migrate/20140207133952_create_documents.rb
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create_table :documents do |t|
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t.binary 'payload'
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end
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# app/models/document.rb
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class Document < ActiveRecord::Base
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end
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# Usage
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data = File.read(Rails.root + "tmp/output.pdf")
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Document.create payload: data
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```
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### Array
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* [type definition](http://www.postgresql.org/docs/9.3/static/arrays.html)
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* [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-array.html)
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```ruby
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# db/migrate/20140207133952_create_books.rb
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create_table :books do |t|
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t.string 'title'
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t.string 'tags', array: true
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t.integer 'ratings', array: true
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end
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add_index :books, :tags, using: 'gin'
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add_index :books, :ratings, using: 'gin'
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# app/models/book.rb
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class Book < ActiveRecord::Base
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end
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# Usage
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Book.create title: "Brave New World",
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tags: ["fantasy", "fiction"],
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ratings: [4, 5]
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## Books for a single tag
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Book.where("'fantasy' = ANY (tags)")
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## Books for multiple tags
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Book.where("tags @> ARRAY[?]::varchar[]", ["fantasy", "fiction"])
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## Books with 3 or more ratings
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Book.where("array_length(ratings, 1) >= 3")
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```
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### Hstore
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* [type definition](http://www.postgresql.org/docs/9.3/static/hstore.html)
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```ruby
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# db/migrate/20131009135255_create_profiles.rb
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ActiveRecord::Schema.define do
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create_table :profiles do |t|
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t.hstore 'settings'
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end
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end
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# app/models/profile.rb
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class Profile < ActiveRecord::Base
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end
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# Usage
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Profile.create(settings: { "color" => "blue", "resolution" => "800x600" })
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profile = Profile.first
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profile.settings # => {"color"=>"blue", "resolution"=>"800x600"}
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profile.settings = {"color" => "yellow", "resolution" => "1280x1024"}
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profile.save!
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## you need to call _will_change! if you are editing the store in place
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profile.settings["color"] = "green"
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profile.settings_will_change!
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profile.save!
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```
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### JSON
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-json.html)
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* [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-json.html)
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```ruby
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# db/migrate/20131220144913_create_events.rb
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create_table :events do |t|
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t.json 'payload'
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end
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# app/models/event.rb
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class Event < ActiveRecord::Base
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end
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# Usage
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Event.create(payload: { kind: "user_renamed", change: ["jack", "john"]})
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event = Event.first
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event.payload # => {"kind"=>"user_renamed", "change"=>["jack", "john"]}
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## Query based on JSON document
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# The -> operator returns the original JSON type (which might be an object), whereas ->> returns text
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Event.where("payload->>'kind' = ?", "user_renamed")
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```
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### Range Types
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* [type definition](http://www.postgresql.org/docs/9.3/static/rangetypes.html)
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* [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-range.html)
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This type is mapped to Ruby [`Range`](http://www.ruby-doc.org/core-2.1.1/Range.html) objects.
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```ruby
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# db/migrate/20130923065404_create_events.rb
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create_table :events do |t|
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t.daterange 'duration'
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end
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# app/models/event.rb
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class Event < ActiveRecord::Base
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end
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# Usage
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Event.create(duration: Date.new(2014, 2, 11)..Date.new(2014, 2, 12))
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event = Event.first
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event.duration # => Tue, 11 Feb 2014...Thu, 13 Feb 2014
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## All Events on a given date
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Event.where("duration @> ?::date", Date.new(2014, 2, 12))
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## Working with range bounds
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event = Event.
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select("lower(duration) AS starts_at").
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select("upper(duration) AS ends_at").first
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event.starts_at # => Tue, 11 Feb 2014
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event.ends_at # => Thu, 13 Feb 2014
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```
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### Composite Types
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* [type definition](http://www.postgresql.org/docs/9.3/static/rowtypes.html)
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Currently there is no special support for composite types. They are mapped to
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normal text columns:
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```sql
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CREATE TYPE full_address AS
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(
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city VARCHAR(90),
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street VARCHAR(90)
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);
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```
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```ruby
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# db/migrate/20140207133952_create_contacts.rb
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execute <<-SQL
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CREATE TYPE full_address AS
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(
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city VARCHAR(90),
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street VARCHAR(90)
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);
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SQL
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create_table :contacts do |t|
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t.column :address, :full_address
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end
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# app/models/contact.rb
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class Contact < ActiveRecord::Base
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end
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# Usage
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Contact.create address: "(Paris,Champs-Élysées)"
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contact = Contact.first
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contact.address # => "(Paris,Champs-Élysées)"
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contact.address = "(Paris,Rue Basse)"
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contact.save!
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```
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### Enumerated Types
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-enum.html)
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Currently there is no special support for enumerated types. They are mapped as
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normal text columns:
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```ruby
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# db/migrate/20131220144913_create_events.rb
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execute <<-SQL
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CREATE TYPE article_status AS ENUM ('draft', 'published');
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SQL
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create_table :articles do |t|
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t.column :status, :article_status
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end
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# app/models/article.rb
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class Article < ActiveRecord::Base
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end
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# Usage
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Article.create status: "draft"
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article = Article.first
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article.status # => "draft"
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article.status = "published"
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article.save!
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```
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### UUID
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-uuid.html)
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* [generator functions](http://www.postgresql.org/docs/9.3/static/uuid-ossp.html)
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```ruby
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# db/migrate/20131220144913_create_revisions.rb
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create_table :revisions do |t|
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t.column :identifier, :uuid
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end
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# app/models/revision.rb
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class Revision < ActiveRecord::Base
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end
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# Usage
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Revision.create identifier: "A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11"
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revision = Revision.first
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revision.identifier # => "a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11"
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```
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### Bit String Types
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-bit.html)
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* [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-bitstring.html)
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```ruby
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# db/migrate/20131220144913_create_users.rb
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create_table :users, force: true do |t|
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t.column :settings, "bit(8)"
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end
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# app/models/device.rb
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class User < ActiveRecord::Base
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end
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# Usage
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User.create settings: "01010011"
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user = User.first
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user.settings # => "(Paris,Champs-Élysées)"
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user.settings = "0xAF"
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user.settings # => 10101111
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user.save!
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```
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### Network Address Types
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-net-types.html)
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The types `inet` and `cidr` are mapped to Ruby
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[`IPAddr`](http://www.ruby-doc.org/stdlib-2.1.1/libdoc/ipaddr/rdoc/IPAddr.html)
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objects. The `macaddr` type is mapped to normal text.
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```ruby
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# db/migrate/20140508144913_create_devices.rb
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create_table(:devices, force: true) do |t|
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t.inet 'ip'
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t.cidr 'network'
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t.macaddr 'address'
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end
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# app/models/device.rb
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class Device < ActiveRecord::Base
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end
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# Usage
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macbook = Device.create(ip: "192.168.1.12",
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network: "192.168.2.0/24",
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address: "32:01:16:6d:05:ef")
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macbook.ip
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# => #<IPAddr: IPv4:192.168.1.12/255.255.255.255>
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macbook.network
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# => #<IPAddr: IPv4:192.168.2.0/255.255.255.0>
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macbook.address
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# => "32:01:16:6d:05:ef"
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```
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### Geometric Types
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* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-geometric.html)
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All geometric types, with the exception of `points` are mapped to normal text.
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A point is casted to an array containing `x` and `y` coordinates.
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UUID Primary Keys
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-----------------
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NOTE: you need to enable the `uuid-ossp` extension to generate UUIDs.
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```ruby
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# db/migrate/20131220144913_create_devices.rb
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enable_extension 'uuid-ossp' unless extension_enabled?('uuid-ossp')
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create_table :devices, id: :uuid, default: 'uuid_generate_v4()' do |t|
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t.string :kind
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end
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# app/models/device.rb
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class Device < ActiveRecord::Base
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end
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# Usage
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device = Device.create
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device.id # => "814865cd-5a1d-4771-9306-4268f188fe9e"
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```
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Full Text Search
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----------------
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```ruby
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# db/migrate/20131220144913_create_documents.rb
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create_table :documents do |t|
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t.string 'title'
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t.string 'body'
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end
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execute "CREATE INDEX documents_idx ON documents USING gin(to_tsvector('english', title || ' ' || body));"
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# app/models/document.rb
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class Document < ActiveRecord::Base
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end
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# Usage
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Document.create(title: "Cats and Dogs", body: "are nice!")
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## all documents matching 'cat & dog'
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Document.where("to_tsvector('english', title || ' ' || body) @@ to_tsquery(?)",
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"cat & dog")
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```
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Database Views
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--------------
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* [view creation](http://www.postgresql.org/docs/9.3/static/sql-createview.html)
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Imagine you need to work with a legacy database containing the following table:
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```
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rails_pg_guide=# \d "TBL_ART"
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Table "public.TBL_ART"
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Column | Type | Modifiers
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------------+-----------------------------+------------------------------------------------------------
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INT_ID | integer | not null default nextval('"TBL_ART_INT_ID_seq"'::regclass)
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STR_TITLE | character varying |
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STR_STAT | character varying | default 'draft'::character varying
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DT_PUBL_AT | timestamp without time zone |
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BL_ARCH | boolean | default false
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Indexes:
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"TBL_ART_pkey" PRIMARY KEY, btree ("INT_ID")
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```
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This table does not follow the Rails conventions at all.
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Because simple PostgreSQL views are updateable by default,
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we can wrap it as follows:
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```ruby
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# db/migrate/20131220144913_create_articles_view.rb
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execute <<-SQL
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CREATE VIEW articles AS
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SELECT "INT_ID" AS id,
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"STR_TITLE" AS title,
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"STR_STAT" AS status,
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"DT_PUBL_AT" AS published_at,
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"BL_ARCH" AS archived
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FROM "TBL_ART"
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WHERE "BL_ARCH" = 'f'
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SQL
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# app/models/article.rb
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class Article < ActiveRecord::Base
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self.primary_key = "id"
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def archive!
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update_attribute :archived, true
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end
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end
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# Usage
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first = Article.create! title: "Winter is coming",
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status: "published",
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published_at: 1.year.ago
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second = Article.create! title: "Brace yourself",
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status: "draft",
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published_at: 1.month.ago
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Article.count # => 1
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first.archive!
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Article.count # => 2
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```
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NOTE: This application only cares about non-archived `Articles`. A view also
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allows for conditions so we can exclude the archived `Articles` directly.
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