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<h2>Active Record and PostgreSQL</h2><p>This guide covers PostgreSQL specific usage of Active Record.</p><p>After reading this guide, you will know:</p>
<ul>
<li>How to use PostgreSQL's datatypes.</li>
<li>How to use UUID primary keys.</li>
<li>How to implement full text search with PostgreSQL.</li>
<li>How to back your Active Record models with database views.</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li>
<a href="#datatypes">Datatypes</a>
<ul>
<li><a href="#bytea">Bytea</a></li>
<li><a href="#array">Array</a></li>
<li><a href="#hstore">Hstore</a></li>
<li><a href="#json">JSON</a></li>
<li><a href="#range-types">Range Types</a></li>
<li><a href="#composite-types">Composite Types</a></li>
<li><a href="#enumerated-types">Enumerated Types</a></li>
<li><a href="#uuid">UUID</a></li>
<li><a href="#bit-string-types">Bit String Types</a></li>
<li><a href="#network-address-types">Network Address Types</a></li>
<li><a href="#geometric-types">Geometric Types</a></li>
</ul>
</li>
<li><a href="#uuid-primary-keys">UUID Primary Keys</a></li>
<li><a href="#full-text-search">Full Text Search</a></li>
<li><a href="#database-views">Database Views</a></li>
</ol>
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<p>In order to use the PostgreSQL adapter you need to have at least version 8.2
installed. Older versions are not supported.</p><p>To get started with PostgreSQL have a look at the
<a href="configuring.html#configuring-a-postgresql-database">configuring Rails guide</a>.
It describes how to properly setup Active Record for PostgreSQL.</p><h3 id="datatypes">1 Datatypes</h3><p>PostgreSQL offers a number of specific datatypes. Following is a list of types,
that are supported by the PostgreSQL adapter.</p><h4 id="bytea">1.1 Bytea</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-binary.html">type definition</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-binarystring.html">functions and operators</a></li>
</ul>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
</pre>
</div>
<h4 id="array">1.2 Array</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/arrays.html">type definition</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-array.html">functions and operators</a></li>
</ul>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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")
</pre>
</div>
<h4 id="hstore">1.3 Hstore</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/hstore.html">type definition</a></li>
</ul>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# db/migrate/20131009135255_create_profiles.rb
ActiveRecord::Schema.define do
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!
## you need to call _will_change! if you are editing the store in place
profile.settings["color"] = "green"
profile.settings_will_change!
profile.save!
</pre>
</div>
<h4 id="json">1.4 JSON</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-json.html">type definition</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-json.html">functions and operators</a></li>
</ul>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
Event.where("payload->'kind' = ?", "user_renamed")
</pre>
</div>
<h4 id="range-types">1.5 Range Types</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/rangetypes.html">type definition</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-range.html">functions and operators</a></li>
</ul>
<p>This type is mapped to Ruby <a href="http://www.ruby-doc.org/core-2.1.1/Range.html"><code>Range</code></a> objects.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
</pre>
</div>
<h4 id="composite-types">1.6 Composite Types</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/rowtypes.html">type definition</a></li>
</ul>
<p>Currently there is no special support for composite types. They are mapped to
normal text columns:</p><div class="code_container">
<pre class="brush: sql; gutter: false; toolbar: false">
CREATE TYPE full_address AS
(
city VARCHAR(90),
street VARCHAR(90)
);
</pre>
</div>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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!
</pre>
</div>
<h4 id="enumerated-types">1.7 Enumerated Types</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-enum.html">type definition</a></li>
</ul>
<p>Currently there is no special support for enumerated types. They are mapped as
normal text columns:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# db/migrate/20131220144913_create_events.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!
</pre>
</div>
<h4 id="uuid">1.8 UUID</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-uuid.html">type definition</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/uuid-ossp.html">generator functions</a></li>
</ul>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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"
</pre>
</div>
<h4 id="bit-string-types">1.9 Bit String Types</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-bit.html">type definition</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-bitstring.html">functions and operators</a></li>
</ul>
<div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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 # => "(Paris,Champs-Élysées)"
user.settings = "0xAF"
user.settings # => 10101111
user.save!
</pre>
</div>
<h4 id="network-address-types">1.10 Network Address Types</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-net-types.html">type definition</a></li>
</ul>
<p>The types <code>inet</code> and <code>cidr</code> are mapped to Ruby
<a href="http://www.ruby-doc.org/stdlib-2.1.1/libdoc/ipaddr/rdoc/IPAddr.html"><code>IPAddr</code></a>
objects. The <code>macaddr</code> type is mapped to normal text.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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"
</pre>
</div>
<h4 id="geometric-types">1.11 Geometric Types</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-geometric.html">type definition</a></li>
</ul>
<p>All geometric types, with the exception of <code>points</code> are mapped to normal text.
A point is casted to an array containing <code>x</code> and <code>y</code> coordinates.</p><h3 id="uuid-primary-keys">2 UUID Primary Keys</h3><div class="note"><p>you need to enable the <code>uuid-ossp</code> extension to generate UUIDs.</p></div><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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"
</pre>
</div>
<h3 id="full-text-search">3 Full Text Search</h3><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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")
</pre>
</div>
<h3 id="database-views">4 Database Views</h3>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/sql-createview.html">view creation</a></li>
</ul>
<p>Imagine you need to work with a legacy database containing the following table:</p><div class="code_container">
<pre class="brush: plain; gutter: false; toolbar: false">
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")
</pre>
</div>
<p>This table does not follow the Rails conventions at all.
Because simple PostgreSQL views are updateable by default,
we can wrap it as follows:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
# 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
</pre>
</div>
<div class="note"><p>This application only cares about non-archived <code>Articles</code>. A view also
allows for conditions so we can exclude the archived <code>Articles</code> directly.</p></div>
<h3>反馈</h3>
<p>
欢迎帮忙改善指南质量。
</p>
<p>
如发现任何错误，欢迎修正。开始贡献前，可先行阅读<a href="http://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#contributing-to-the-rails-documentation">贡献指南：文档</a>。
</p>
<p>翻译如有错误，深感抱歉，欢迎 <a href="https://github.com/ruby-china/guides/fork">Fork</a> 修正，或至此处<a href="https://github.com/ruby-china/guides/issues/new">回报</a>。</p>
<p>
文章可能有未完成或过时的内容。请先检查 <a href="http://edgeguides.rubyonrails.org">Edge Guides</a> 来确定问题在 master 是否已经修掉了。再上 master 补上缺少的文件。内容参考 <a href="ruby_on_rails_guides_guidelines.html">Ruby on Rails 指南准则</a>来了解行文风格。
</p>
<p>最后，任何关于 Ruby on Rails 文档的讨论，欢迎到 <a href="http://groups.google.com/group/rubyonrails-docs">rubyonrails-docs 邮件群组</a>。
</p>
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