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