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<h2>Active Record PostgreSQL</h2><p>本篇介紹 Active Record PostgreSQL 的具體用法。</p><p>讀完本篇，您將了解：</p>
<ul>
<li>如何使用 PostgreSQL 的資料類型。</li>
<li>如何使用 UUID 主鍵。</li>
<li>如何在 PostgreSQL 實作全文搜索。</li>
<li>如何用 資料庫的 View 來支援 Active Record Model。</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li>
<a href="#%E8%B3%87%E6%96%99%E9%A1%9E%E5%9E%8B">資料類型</a>
<ul>
<li><a href="#bytea-%E9%A1%9E%E5%9E%8B">Bytea 類型</a></li>
<li><a href="#%E9%99%A3%E5%88%97%E9%A1%9E%E5%9E%8B">陣列類型</a></li>
<li><a href="#hstore-%E9%A1%9E%E5%9E%8B">Hstore 類型</a></li>
<li><a href="#json-%E9%A1%9E%E5%9E%8B">JSON 類型</a></li>
<li><a href="#range-%E9%A1%9E%E5%9E%8B">Range 類型</a></li>
<li><a href="#%E8%A4%87%E5%90%88%E9%A1%9E%E5%9E%8B">複合類型</a></li>
<li><a href="#%E6%9E%9A%E8%88%89%E9%A1%9E%E5%9E%8B">枚舉類型</a></li>
<li><a href="#uuid-%E9%A1%9E%E5%9E%8B">UUID 類型</a></li>
<li><a href="#%E4%BD%8D%E5%85%83%E5%AD%97%E4%B8%B2%E9%A1%9E%E5%9E%8B">位元字串類型</a></li>
<li><a href="#%E7%B6%B2%E8%B7%AF%E4%BD%8D%E5%9D%80%E9%A1%9E%E5%9E%8B">網路位址類型</a></li>
<li><a href="#%E5%B9%BE%E4%BD%95%E9%A1%9E%E5%9E%8B">幾何類型</a></li>
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<li><a href="#%E5%85%A8%E6%96%87%E6%90%9C%E7%B4%A2">全文搜索</a></li>
<li><a href="#%E8%B3%87%E6%96%99%E5%BA%AB-views">資料庫 Views</a></li>
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<p>PostgreSQL 的最低版本要求為 8.2。舊版不支援。</p><p>開始使用 PostgreSQL 之前，請先看看<a href="configuring.html#configuring-a-postgresql-database">如何為 Active Record 設定 PostgreSQL 資料庫</a>。</p><h3 id="資料類型">1 資料類型</h3><p>PostgreSQL 提供許多具體的資料類型。以下是 PostgreSQL 連接器所支援的類型列表。</p><h4 id="bytea-類型">1.1 Bytea 類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-binary.html">類型定義</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-binarystring.html">函式與運算元</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
# 用途
data = File.read(Rails.root + "tmp/output.pdf")
Document.create payload: data
</pre>
</div>
<h4 id="陣列類型">1.2 陣列類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/arrays.html">類型定義</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-array.html">函式與運算元</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
# 用途
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-類型">1.3 Hstore 類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/hstore.html">類型定義</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
# 用途
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-類型">1.4 JSON 類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-json.html">類型定義</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-json.html">函式與運算元</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
# 用途
Event.create(payload: { kind: "user_renamed", change: ["jack", "john"]})
event = Event.first
event.payload # => {"kind"=>"user_renamed", "change"=>["jack", "john"]}
## 基於 JSON 文件的查詢
Event.where("payload->'kind' = ?", "user_renamed")
</pre>
</div>
<h4 id="range-類型">1.5 Range 類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/rangetypes.html">類型定義</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-range.html">函式與運算元</a></li>
</ul>
<p>此類型映射到 Ruby 的 <a href="http://www.ruby-doc.org/core-2.1.1/Range.html"><code>Range</code></a> 物件</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
# 用途
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
## 找出特定日期的所有活動
Event.where("duration @> ?::date", Date.new(2014, 2, 12))
## 使用 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="複合類型">1.6 複合類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/rowtypes.html">類型定義</a></li>
</ul>
<p>複合類型映射到一般的 <code>text</code> 欄位。</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
# 用途
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="枚舉類型">1.7 枚舉類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-enum.html">類型定義</a></li>
</ul>
<p>枚舉類型映射到一般的 <code>text</code> 欄位。</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
# 用途
Article.create status: "draft"
article = Article.first
article.status # => "draft"
article.status = "published"
article.save!
</pre>
</div>
<h4 id="uuid-類型">1.8 UUID 類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-uuid.html">類型定義</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/uuid-ossp.html">產生器函式</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
# 用途
Revision.create identifier: "A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11"
revision = Revision.first
revision.identifier # => "a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11"
</pre>
</div>
<h4 id="位元字串類型">1.9 位元字串類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-bit.html">類型定義</a></li>
<li><a href="http://www.postgresql.org/docs/9.3/static/functions-bitstring.html">函式與運算元</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
# 用途
User.create settings: "01010011"
user = User.first
user.settings # => "(Paris,Champs-Élysées)"
user.settings = "0xAF"
user.settings # => 10101111
user.save!
</pre>
</div>
<h4 id="網路位址類型">1.10 網路位址類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-net-types.html">類型定義</a></li>
</ul>
<p><code>inet</code> 與 <code>cidr</code> 類型映射到 Ruby 的 <a href="http://www.ruby-doc.org/stdlib-2.1.1/libdoc/ipaddr/rdoc/IPAddr.html"><code>IPAddr</code></a> 物件。<code>macaddr</code> 類型映射到一般的 <code>text</code> 欄位。</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="幾何類型">1.11 幾何類型</h4>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/datatype-geometric.html">類型定義</a></li>
</ul>
<p>幾何類型（除了 <code>points</code>）映射到一般的 <code>text</code> 欄位。
<code>point</code> 會轉成陣列，陣列裡有 x、y 軸。</p><h3 id="uuid-主鍵">2 UUID 主鍵</h3><div class="note"><p>需要啟用 <code>uuid-ossp</code> 擴充功能才可以產生 UUID。</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
# 用途
device = Device.create
device.id # => "814865cd-5a1d-4771-9306-4268f188fe9e"
</pre>
</div>
<h3 id="全文搜索">3 全文搜索</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
# 用途
Document.create(title: "Cats and Dogs", body: "are nice!")
## 所有匹配 `cat & dog` 的文件
Document.where("to_tsvector('english', title || ' ' || body) @@ to_tsquery(?)",
"cat & dog")
</pre>
</div>
<h3 id="資料庫-views">4 資料庫 Views</h3>
<ul>
<li><a href="http://www.postgresql.org/docs/9.3/static/sql-createview.html">建立 View</a></li>
</ul>
<p>假設需要處理老舊的資料庫，資料表如下：</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>這張資料表完全沒有遵循 Rails 的慣例。
因為簡單的 PostgreSQL View 預設便可以更新了，可以像下面這樣包起來：</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>這個應用程式只專注在尚未歸檔的 <code>Articles</code>。View 也允許使用條件式，所以我們可以直接排除掉已歸檔的 <code>Articles</code>。</p></div>
<h3>反饋</h3>
<p>
歡迎幫忙改善指南的品質。
</p>
<p>
如發現任何錯誤之處，歡迎修正。開始貢獻前，可以先閱讀<a href="http://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#contributing-to-the-rails-documentation">貢獻指南：文件</a>。
</p>
<p>翻譯如有錯誤，深感抱歉，歡迎 <a href="https://github.com/docrails-tw/guides/fork">Fork</a> 修正，或至此處<a href="https://github.com/docsrails-tw/guides/issues/new">回報</a>。</p>
<p>
文章可能有未完成或過時的內容。請先檢查 <a href="http://edgeguides.rubyonrails.org">Edge Guides</a> 來確定問題在 master 是否已經修掉了。再上 master 補上缺少的文件。內容參考 <a href="ruby_on_rails_guides_guidelines.html">Ruby on Rails 指南準則</a>來了解行文風格。
</p>
<p>最後，任何關於 Ruby on Rails 文件的討論，歡迎至 <a href="http://groups.google.com/group/rubyonrails-docs">rubyonrails-docs 郵件論壇</a>。
</p>
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