pg guide, datatypes and examples. [ci skip]

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+eActive Record and PostgreSQL
+============================
+
+This guide goes over PostgreSQL specific usage of Active Record.
+
+How to use the PostgreSQL adapter for Active Record is described in the
+[configuring Rails guide](configuring.html#configuring-a-postgresql-database).
+
+In order to use the PostgreSQL adapter you need to have at least version 8.2
+installed. Older versions are not supported.
+
+Datatypes
+---------
+
+PostgreSQL offers a number of specific datatypes. Following is a list of types,
+that are supported by the PostgreSQL adapter.
+
+### Bytea
+
+* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-binary.html)
+* [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-binarystring.html)
+
+```ruby
+# 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
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/arrays.html)
+  * [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-array.html)
+
+```ruby
+# db/migrate/20140207133952_create_books.rb
+create_table :book do |t|
+  t.string 'title'
+  t.string 'tags', array: true
+  t.integer 'ratings', array: true
+end
+
+# 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
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/hstore.html)
+
+```ruby
+# 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", "resulution" => "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!
+```
+
+### Json
+
+ * [type definition](http://www.postgresql.org/docs/9.3/static/datatype-json.html)
+ * [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-json.html)
+
+```ruby
+# 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")
+```
+
+### Range Types
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/rangetypes.html)
+  * [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-range.html)
+
+This type is mapped to Ruby [`Range`]() objects.
+
+```ruby
+# 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
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/rowtypes.html)
+
+Currently there is no special support for composite types. They are mapped to as
+normal text columns:
+
+```sql
+CREATE TYPE full_address AS
+(
+  city VARCHAR(90),
+  street VARCHAR(90)
+);
+```
+
+```ruby
+# 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
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/datatype-enum.html)
+
+Currently there is no special support for enumerated types. They are mapped as
+normal text columns:
+
+```ruby
+# 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!
+```
+
+### UUID
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/datatype-uuid.html)
+  * [generator functions](http://www.postgresql.org/docs/9.3/static/uuid-ossp.html)
+
+
+```ruby
+# 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"
+```
+
+#### as primary key
+
+```ruby
+# 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"
+```
+
+### Bit String Types
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/datatype-bit.html)
+  * [functions and operators](http://www.postgresql.org/docs/9.3/static/functions-bitstring.html)
+
+```ruby
+# 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!
+```
+
+### Network Address Types
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/datatype-net-types.html)
+
+The types `inet` and `cidr` are mapped to Ruby [`IPAddr`]() objects. The
+`macaddr` type is mapped to normal text.
+
+### Geometric Types
+
+  * [type definition](http://www.postgresql.org/docs/9.3/static/datatype-geometric.html)
+
+All geometric types are mapped to normal text.
+
+Views
+-----