Active Record and PostgreSQL
============================

This guide covers PostgreSQL specific usage of Active Record.

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](configuring.html#configuring-a-postgresql-database).
It describes how to properly setup Active Record for PostgreSQL.

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.

--------------------------------------------------------------------------------

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", "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!
```

### 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`](http://www.ruby-doc.org/core-2.1.1/Range.html) 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"
```

### 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`](http://www.ruby-doc.org/stdlib-2.1.1/libdoc/ipaddr/rdoc/IPAddr.html) objects. The
`macaddr` type is mapped to normal text.

```ruby
# 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

* [type definition](http://www.postgresql.org/docs/9.3/static/datatype-geometric.html)

All geometric types are mapped to normal text.


UUID Primary Keys
-----------------

NOTE: you need to enable the `uuid-ossp` extension to generate UUIDs.

```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"
```

Full Text Search
----------------

```ruby
# 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")
```

Views
-----

* [view creation](http://www.postgresql.org/docs/9.3/static/sql-createview.html)

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:

```ruby
# 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!
p 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.