pg_search

DESCRIPTION

PgSearch builds named scopes that take advantage of PostgreSQL's full text search.

Read the blog post introducing PgSearch at https://tanzu.vmware.com/content/blog/pg-search-how-i-learned-to-stop-worrying-and-love-postgresql-full-text-search

REQUIREMENTS

Ruby 2.6+
ActiveRecord 5.2+
PostgreSQL 9.2+
PostgreSQL extensions for certain features

INSTALL

$ gem install pg_search

or add this line to your Gemfile:

gem 'pg_search'

Non-Rails projects

In addition to installing and requiring the gem, you may want to include the PgSearch rake tasks in your Rakefile. This isn't necessary for Rails projects, which gain the Rake tasks via a Railtie.

load "pg_search/tasks.rb"

USAGE

To add PgSearch to an Active Record model, simply include the PgSearch module.

class Shape < ActiveRecord::Base
  include PgSearch::Model
end

Multi-search vs. search scopes

pg_search supports two different techniques for searching, multi-search and search scopes.

The first technique is multi-search, in which records of many different Active Record classes can be mixed together into one global search index across your entire application. Most sites that want to support a generic search page will want to use this feature.

The other technique is search scopes, which allow you to do more advanced searching against only one Active Record class. This is more useful for building things like autocompleters or filtering a list of items in a faceted search.

Multi-search

Setup

Before using multi-search, you must generate and run a migration to create the pg_search_documents database table.

$ rails g pg_search:migration:multisearch
$ rake db:migrate

multisearchable

To add a model to the global search index for your application, call multisearchable in its class definition.

class EpicPoem < ActiveRecord::Base
  include PgSearch::Model
  multisearchable against: [:title, :author]
end

class Flower < ActiveRecord::Base
  include PgSearch::Model
  multisearchable against: :color
end

If this model already has existing records, you will need to reindex this model to get existing records into the pg_search_documents table. See the rebuild task below.

Whenever a record is created, updated, or destroyed, an Active Record callback will fire, leading to the creation of a corresponding PgSearch::Document record in the pg_search_documents table. The :against option can be one or several methods which will be called on the record to generate its search text.

You can also pass a Proc or method name to call to determine whether or not a particular record should be included.

class Convertible < ActiveRecord::Base
  include PgSearch::Model
  multisearchable against: [:make, :model],
                  if: :available_in_red?
end

class Jalopy < ActiveRecord::Base
  include PgSearch::Model
  multisearchable against: [:make, :model],
                  if: lambda { |record| record.model_year > 1970 }
end

Note that the Proc or method name is called in an after_save hook. This means that you should be careful when using Time or other objects. In the following example, if the record was last saved before the published_at timestamp, it won't get listed in global search at all until it is touched again after the timestamp.

class AntipatternExample
  include PgSearch::Model
  multisearchable against: [:contents],
                  if: :published?

  def published?
    published_at < Time.now
  end
end

problematic_record = AntipatternExample.create!(
  contents: "Using :if with a timestamp",
  published_at: 10.minutes.from_now
)

problematic_record.published?     # => false
PgSearch.multisearch("timestamp") # => No results

sleep 20.minutes

problematic_record.published?     # => true
PgSearch.multisearch("timestamp") # => No results

problematic_record.save!

problematic_record.published?     # => true
PgSearch.multisearch("timestamp") # => Includes problematic_record

More Options

Conditionally update pg_search_documents

You can specify an :update_if parameter to conditionally update pg_search documents. For example:

multisearchable(
    against: [:body],
    update_if: :body_changed?
  )

Specify additional attributes to be saved on the pg_search_documents table

You can specify :additional_attributes to be saved within the pg_search_documents table. For example, perhaps you are indexing a book model and an article model and wanted to include the author_id.

First, we need to add a reference to author to the migration creating our pg_search_documents table.

  create_table :pg_search_documents do |t|
    t.text :content
    t.references :author, index: true
    t.belongs_to :searchable, polymorphic: true, index: true
    t.timestamps null: false
  end

Then, we can send in this additional attribute in a lambda

  multisearchable(
    against: [:title, :body],
    additional_attributes: -> (article) { { author_id: article.author_id } }
  )

This allows much faster searches without joins later on by doing something like:

PgSearch.multisearch(params['search']).where(author_id: 2)

NOTE: You must currently manually call record.update_pg_search_document for the additional attribute to be included in the pg_search_documents table

Multi-search associations

Two associations are built automatically. On the original record, there is a has_one :pg_search_document association pointing to the PgSearch::Document record, and on the PgSearch::Document record there is a belongs_to :searchable polymorphic association pointing back to the original record.

odyssey = EpicPoem.create!(title: "Odyssey", author: "Homer")
search_document = odyssey.pg_search_document #=> PgSearch::Document instance
search_document.searchable #=> #<EpicPoem id: 1, title: "Odyssey", author: "Homer">

Searching in the global search index

To fetch the PgSearch::Document entries for all of the records that match a given query, use PgSearch.multisearch.

odyssey = EpicPoem.create!(title: "Odyssey", author: "Homer")
rose = Flower.create!(color: "Red")
PgSearch.multisearch("Homer") #=> [#<PgSearch::Document searchable: odyssey>]
PgSearch.multisearch("Red") #=> [#<PgSearch::Document searchable: rose>]

Chaining method calls onto the results

PgSearch.multisearch returns an ActiveRecord::Relation, just like scopes do, so you can chain scope calls to the end. This works with gems like Kaminari that add scope methods. Just like with regular scopes, the database will only receive SQL requests when necessary.

PgSearch.multisearch("Bertha").limit(10)
PgSearch.multisearch("Juggler").where(searchable_type: "Occupation")
PgSearch.multisearch("Alamo").page(3).per(30)
PgSearch.multisearch("Diagonal").find_each do |document|
  puts document.searchable.updated_at
end
PgSearch.multisearch("Moro").reorder("").group(:searchable_type).count(:all)
PgSearch.multisearch("Square").includes(:searchable)

Configuring multi-search

PgSearch.multisearch can be configured using the same options as pg_search_scope (explained in more detail below). Just set the PgSearch.multisearch_options in an initializer:

PgSearch.multisearch_options = {
  using: [:tsearch, :trigram],
  ignoring: :accents
}

Rebuilding search documents for a given class

If you change the :against option on a class, add multisearchable to a class that already has records in the database, or remove multisearchable from a class in order to remove it from the index, you will find that the pg_search_documents table could become out-of-sync with the actual records in your other tables.

The index can also become out-of-sync if you ever modify records in a way that does not trigger Active Record callbacks. For instance, the #update_attribute instance method and the .update_all class method both skip callbacks and directly modify the database.

To remove all of the documents for a given class, you can simply delete all of the PgSearch::Document records.

PgSearch::Document.delete_by(searchable_type: "Animal")

To regenerate the documents for a given class, run:

PgSearch::Multisearch.rebuild(Product)

The rebuild method will delete all the documents for the given class before regenerating them. In some situations this may not be desirable, such as when you're using single-table inheritance and searchable_type is your base class. You can prevent rebuild from deleting your records like so:

PgSearch::Multisearch.rebuild(Product, clean_up: false)

rebuild runs inside a single transaction. To run outside of a transaction, you can pass transactional: false like so:

PgSearch::Multisearch.rebuild(Product, transactional: false)

Rebuild is also available as a Rake task, for convenience.

$ rake pg_search:multisearch:rebuild[BlogPost]

A second optional argument can be passed to specify the PostgreSQL schema search path to use, for multi-tenant databases that have multiple pg_search_documents tables. The following will set the schema search path to "my_schema" before reindexing.

$ rake pg_search:multisearch:rebuild[BlogPost,my_schema]

For models that are multisearchable :against methods that directly map to Active Record attributes, an efficient single SQL statement is run to update the pg_search_documents table all at once. However, if you call any dynamic methods in :against, the following strategy will be used:

PgSearch::Document.delete_all(searchable_type: "Ingredient")
Ingredient.find_each { |record| record.update_pg_search_document }

You can also provide a custom implementation for rebuilding the documents by adding a class method called rebuild_pg_search_documents to your model.

class Movie < ActiveRecord::Base
  belongs_to :director

  def director_name
    director.name
  end

  multisearchable against: [:name, :director_name]

  # Naive approach
  def self.rebuild_pg_search_documents
    find_each { |record| record.update_pg_search_document }
  end

  # More sophisticated approach
  def self.rebuild_pg_search_documents
    connection.execute <<~SQL.squish
     INSERT INTO pg_search_documents (searchable_type, searchable_id, content, created_at, updated_at)
       SELECT 'Movie' AS searchable_type,
              movies.id AS searchable_id,
              CONCAT_WS(' ', movies.name, directors.name) AS content,
              now() AS created_at,
              now() AS updated_at
       FROM movies
       LEFT JOIN directors
         ON directors.id = movies.director_id
    SQL
  end
end

Note: If using PostgreSQL before 9.1, replace the CONCAT_WS() function call with double-pipe concatenation, eg. (movies.name || ' ' || directors.name). However, now be aware that if any of the joined values is NULL then the final content value will also be NULL, whereas CONCAT_WS() will selectively ignore NULL values.

Disabling multi-search indexing temporarily

If you have a large bulk operation to perform, such as importing a lot of records from an external source, you might want to speed things up by turning off indexing temporarily. You could then use one of the techniques above to rebuild the search documents off-line.

PgSearch.disable_multisearch do
  Movie.import_from_xml_file(File.open("movies.xml"))
end

pg_search_scope

You can use pg_search_scope to build a search scope. The first parameter is a scope name, and the second parameter is an options hash. The only required option is :against, which tells pg_search_scope which column or columns to search against.

Searching against one column

To search against a column, pass a symbol as the :against option.

class BlogPost < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_by_title, against: :title
end

We now have an ActiveRecord scope named search_by_title on our BlogPost model. It takes one parameter, a search query string.

BlogPost.create!(title: "Recent Developments in the World of Pastrami")
BlogPost.create!(title: "Prosciutto and You: A Retrospective")
BlogPost.search_by_title("pastrami") # => [#<BlogPost id: 2, title: "Recent Developments in the World of Pastrami">]

Searching against multiple columns

Just pass an Array if you'd like to search more than one column.

class Person < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_by_full_name, against: [:first_name, :last_name]
end

Now our search query can match either or both of the columns.

person_1 = Person.create!(first_name: "Grant", last_name: "Hill")
person_2 = Person.create!(first_name: "Hugh", last_name: "Grant")

Person.search_by_full_name("Grant") # => [person_1, person_2]
Person.search_by_full_name("Grant Hill") # => [person_1]

Dynamic search scopes

Just like with Active Record named scopes, you can pass in a Proc object that returns a hash of options. For instance, the following scope takes a parameter that dynamically chooses which column to search against.

Important: The returned hash must include a :query key. Its value does not necessary have to be dynamic. You could choose to hard-code it to a specific value if you wanted.

class Person < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_by_name, lambda { |name_part, query|
    raise ArgumentError unless [:first, :last].include?(name_part)
    {
      against: name_part,
      query: query
    }
  }
end

person_1 = Person.create!(first_name: "Grant", last_name: "Hill")
person_2 = Person.create!(first_name: "Hugh", last_name: "Grant")

Person.search_by_name :first, "Grant" # => [person_1]
Person.search_by_name :last, "Grant" # => [person_2]

Searching through associations

It is possible to search columns on associated models. Note that if you do this, it will be impossible to speed up searches with database indexes. However, it is supported as a quick way to try out cross-model searching.

You can pass a Hash into the :associated_against option to set up searching through associations. The keys are the names of the associations and the value works just like an :against option for the other model. Right now, searching deeper than one association away is not supported. You can work around this by setting up a series of :through associations to point all the way through.

class Cracker < ActiveRecord::Base
  has_many :cheeses
end

class Cheese < ActiveRecord::Base
end

class Salami < ActiveRecord::Base
  include PgSearch::Model

  belongs_to :cracker
  has_many :cheeses, through: :cracker

  pg_search_scope :tasty_search, associated_against: {
    cheeses: [:kind, :brand],
    cracker: :kind
  }
end

salami_1 = Salami.create!
salami_2 = Salami.create!
salami_3 = Salami.create!

limburger = Cheese.create!(kind: "Limburger")
brie = Cheese.create!(kind: "Brie")
pepper_jack = Cheese.create!(kind: "Pepper Jack")

Cracker.create!(kind: "Black Pepper", cheeses: [brie], salami: salami_1)
Cracker.create!(kind: "Ritz", cheeses: [limburger, pepper_jack], salami: salami_2)
Cracker.create!(kind: "Graham", cheeses: [limburger], salami: salami_3)

Salami.tasty_search("pepper") # => [salami_1, salami_2]

Searching using different search features

By default, pg_search_scope uses the built-in PostgreSQL text search. If you pass the :using option to pg_search_scope, you can choose alternative search techniques.

class Beer < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_name, against: :name, using: [:tsearch, :trigram, :dmetaphone]
end

The currently implemented features are

:tsearch - Full text search, which is built-in to PostgreSQL
:trigram - Trigram search, which requires the trigram extension
:dmetaphone - Double Metaphone search, which requires the fuzzystrmatch extension

:tsearch (Full Text Search)

PostgreSQL's built-in full text search supports weighting, prefix searches, and stemming in multiple languages.

Weighting

Each searchable column can be given a weight of "A", "B", "C", or "D". Columns with earlier letters are weighted higher than those with later letters. So, in the following example, the title is the most important, followed by the subtitle, and finally the content.

class NewsArticle < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_full_text, against: {
    title: 'A',
    subtitle: 'B',
    content: 'C'
  }
end

You can also pass the weights in as an array of arrays, or any other structure that responds to #each and yields either a single symbol or a symbol and a weight. If you omit the weight, a default will be used.

class NewsArticle < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_full_text, against: [
    [:title, 'A'],
    [:subtitle, 'B'],
    [:content, 'C']
  ]
end

class NewsArticle < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_full_text, against: [
    [:title, 'A'],
    {subtitle: 'B'},
    :content
  ]
end

:prefix (PostgreSQL 8.4 and newer only)

PostgreSQL's full text search matches on whole words by default. If you want to search for partial words, however, you can set :prefix to true. Since this is a :tsearch-specific option, you should pass it to :tsearch directly, as shown in the following example.

class Superhero < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :whose_name_starts_with,
                  against: :name,
                  using: {
                    tsearch: { prefix: true }
                  }
end

batman = Superhero.create name: 'Batman'
batgirl = Superhero.create name: 'Batgirl'
robin = Superhero.create name: 'Robin'

Superhero.whose_name_starts_with("Bat") # => [batman, batgirl]

:negation

PostgreSQL's full text search matches all search terms by default. If you want to exclude certain words, you can set :negation to true. Then any term that begins with an exclamation point ! will be excluded from the results. Since this is a :tsearch-specific option, you should pass it to :tsearch directly, as shown in the following example.

Note that combining this with other search features can have unexpected results. For example, :trigram searches don't have a concept of excluded terms, and thus if you use both :tsearch and :trigram in tandem, you may still find results that contain the term that you were trying to exclude.

class Animal < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :with_name_matching,
                  against: :name,
                  using: {
                    tsearch: {negation: true}
                  }
end

one_fish = Animal.create(name: "one fish")
two_fish = Animal.create(name: "two fish")
red_fish = Animal.create(name: "red fish")
blue_fish = Animal.create(name: "blue fish")

Animal.with_name_matching("fish !red !blue") # => [one_fish, two_fish]

:dictionary

PostgreSQL full text search also support multiple dictionaries for stemming. You can learn more about how dictionaries work by reading the PostgreSQL documention. If you use one of the language dictionaries, such as "english", then variants of words (e.g. "jumping" and "jumped") will match each other. If you don't want stemming, you should pick the "simple" dictionary which does not do any stemming. If you don't specify a dictionary, the "simple" dictionary will be used.

class BoringTweet < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :kinda_matching,
                  against: :text,
                  using: {
                    tsearch: {dictionary: "english"}
                  }
  pg_search_scope :literally_matching,
                  against: :text,
                  using: {
                    tsearch: {dictionary: "simple"}
                  }
end

sleepy = BoringTweet.create! text: "I snoozed my alarm for fourteen hours today. I bet I can beat that tomorrow! #sleepy"
sleeping = BoringTweet.create! text: "You know what I like? Sleeping. That's what. #enjoyment"
sleeper = BoringTweet.create! text: "Have you seen Woody Allen's movie entitled Sleeper? Me neither. #boycott"

BoringTweet.kinda_matching("sleeping") # => [sleepy, sleeping, sleeper]
BoringTweet.literally_matching("sleeping") # => [sleeping]

:normalization

PostgreSQL supports multiple algorithms for ranking results against queries. For instance, you might want to consider overall document size or the distance between multiple search terms in the original text. This option takes an integer, which is passed directly to PostgreSQL. According to the latest PostgreSQL documentation, the supported algorithms are:

0 (the default) ignores the document length
1 divides the rank by 1 + the logarithm of the document length
2 divides the rank by the document length
4 divides the rank by the mean harmonic distance between extents
8 divides the rank by the number of unique words in document
16 divides the rank by 1 + the logarithm of the number of unique words in document
32 divides the rank by itself + 1

This integer is a bitmask, so if you want to combine algorithms, you can add their numbers together. (e.g. to use algorithms 1, 8, and 32, you would pass 1 + 8 + 32 = 41)

class BigLongDocument < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :regular_search,
                  against: :text

  pg_search_scope :short_search,
                  against: :text,
                  using: {
                    tsearch: {normalization: 2}
                  }

long = BigLongDocument.create!(text: "Four score and twenty years ago")
short = BigLongDocument.create!(text: "Four score")

BigLongDocument.regular_search("four score") #=> [long, short]
BigLongDocument.short_search("four score") #=> [short, long]

:any_word

Setting this attribute to true will perform a search which will return all models containing any word in the search terms.

class Number < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search_any_word,
                  against: :text,
                  using: {
                    tsearch: {any_word: true}
                  }

  pg_search_scope :search_all_words,
                  against: :text
end

one = Number.create! text: 'one'
two = Number.create! text: 'two'
three = Number.create! text: 'three'

Number.search_any_word('one two three') # => [one, two, three]
Number.search_all_words('one two three') # => []

:sort_only

Setting this attribute to true will make this feature available for sorting, but will not include it in the query's WHERE condition.

class Person < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search,
                  against: :name,
                  using: {
                    tsearch: {any_word: true},
                    dmetaphone: {any_word: true, sort_only: true}
                  }
end

exact = Person.create!(name: 'ash hines')
one_exact_one_close = Person.create!(name: 'ash heinz')
one_exact = Person.create!(name: 'ash smith')
one_close = Person.create!(name: 'leigh heinz')

Person.search('ash hines') # => [exact, one_exact_one_close, one_exact]

:highlight

Adding .with_pg_search_highlight after the pg_search_scope you can access to pg_highlight attribute for each object.

class Person < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :search,
                  against: :bio,
                  using: {
                    tsearch: {
                      highlight: {
                        StartSel: '<b>',
                        StopSel: '</b>',
                        MaxWords: 123,
                        MinWords: 456,
                        ShortWord: 4,
                        HighlightAll: true,
                        MaxFragments: 3,
                        FragmentDelimiter: '&hellip;'
                      }
                    }
                  }
end

Person.create!(:bio => "Born in rural Alberta, where the buffalo roam.")

first_match = Person.search("Alberta").with_pg_search_highlight.first
first_match.pg_search_highlight # => "Born in rural <b>Alberta</b>, where the buffalo roam."

The highlight option accepts all options supported by ts_headline, and uses PostgreSQL's defaults.

See the documentation for details on the meaning of each option.

:dmetaphone (Double Metaphone soundalike search)

Double Metaphone is an algorithm for matching words that sound alike even if they are spelled very differently. For example, "Geoff" and "Jeff" sound identical and thus match. Currently, this is not a true double-metaphone, as only the first metaphone is used for searching.

Double Metaphone support is currently available as part of the fuzzystrmatch extension that must be installed before this feature can be used. In addition to the extension, you must install a utility function into your database. To generate and run a migration for this, run:

$ rails g pg_search:migration:dmetaphone
$ rake db:migrate

The following example shows how to use :dmetaphone.

class Word < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :that_sounds_like,
                  against: :spelling,
                  using: :dmetaphone
end

four = Word.create! spelling: 'four'
far = Word.create! spelling: 'far'
fur = Word.create! spelling: 'fur'
five = Word.create! spelling: 'five'

Word.that_sounds_like("fir") # => [four, far, fur]

:trigram (Trigram search)

Trigram search works by counting how many three-letter substrings (or "trigrams") match between the query and the text. For example, the string "Lorem ipsum" can be split into the following trigrams:

[" Lo", "Lor", "ore", "rem", "em ", "m i", " ip", "ips", "psu", "sum", "um ", "m  "]

Trigram search has some ability to work even with typos and misspellings in the query or text.

Trigram support is currently available as part of the pg_trgm extension that must be installed before this feature can be used.

class Website < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :kinda_spelled_like,
                  against: :name,
                  using: :trigram
end

yahooo = Website.create! name: "Yahooo!"
yohoo = Website.create! name: "Yohoo!"
gogle = Website.create! name: "Gogle"
facebook = Website.create! name: "Facebook"

Website.kinda_spelled_like("Yahoo!") # => [yahooo, yohoo]

:threshold

By default, trigram searches find records which have a similarity of at least 0.3 using pg_trgm's calculations. You may specify a custom threshold if you prefer. Higher numbers match more strictly, and thus return fewer results. Lower numbers match more permissively, letting in more results. Please note that setting a trigram threshold will force a table scan as the derived query uses the similarity() function instead of the % operator.

class Vegetable < ActiveRecord::Base
  include PgSearch::Model

  pg_search_scope :strictly_spelled_like,
                  against: :name,
                  using: {
                    trigram: {
                      threshold: 0.5
                    }
                  }

  pg_search_scope :roughly_spelled_like,
                  against: :name,
                  using: {
                    trigram: {
                      threshold: 0.1
                    }
                  }
end

cauliflower = Vegetable.create! name: "cauliflower"

Vegetable.roughly_spelled_like("couliflower") # => [cauliflower]
Vegetable.strictly_spelled_like("couliflower") # => [cauliflower]

Vegetable.roughly_spelled_like("collyflower") # => [cauliflower]
Vegetable.strictly_spelled_like("collyflower") # => []

:word_similarity

Allows you to match words in longer strings. By default, trigram searches use % or similarity() as a similarity value. Set word_similarity to true to opt for <% and word_similarity instead. This causes the trigram search to use the similarity of the query term and the word with greatest similarity.

class Sentence < ActiveRecord::Base
  include PgSearch::Model

  pg_search_scope :similarity_like,
                  against: :name,
                  using: {
                    trigram: {
                      word_similarity: true
                    }
                  }

  pg_search_scope :word_similarity_like,
                  against: :name,
                  using: [:trigram]
end

sentence = Sentence.create! name: "Those are two words."

Sentence.similarity_like("word") # => []
Sentence.word_similarity_like("word") # => [sentence]

Limiting Fields When Combining Features

Sometimes when doing queries combining different features you might want to searching against only some of the fields with certain features. For example perhaps you want to only do a trigram search against the shorter fields so that you don't need to reduce the threshold excessively. You can specify which fields using the 'only' option:

class Image < ActiveRecord::Base
  include PgSearch::Model

  pg_search_scope :combined_search,
                  against: [:file_name, :short_description, :long_description]
                  using: {
                    tsearch: { dictionary: 'english' },
                    trigram: {
                      only: [:file_name, :short_description]
                    }
                  }

end

Now you can succesfully retrieve an Image with a file_name: 'image_foo.jpg' and long_description: 'This description is so long that it would make a trigram search fail any reasonable threshold limit' with:

Image.combined_search('reasonable') # found with tsearch
Image.combined_search('foo') # found with trigram

Ignoring accent marks

Most of the time you will want to ignore accent marks when searching. This makes it possible to find words like "piñata" when searching with the query "pinata". If you set a pg_search_scope to ignore accents, it will ignore accents in both the searchable text and the query terms.

Ignoring accents uses the unaccent extension that must be installed before this feature can be used.

class SpanishQuestion < ActiveRecord::Base
  include PgSearch::Model
  pg_search_scope :gringo_search,
                  against: :word,
                  ignoring: :accents
end

what = SpanishQuestion.create(word: "Qué")
how_many = SpanishQuestion.create(word: "Cuánto")
how = SpanishQuestion.create(word: "Cómo")

SpanishQuestion.gringo_search("Que") # => [what]
SpanishQuestion.gringo_search("Cüåñtô") # => [how_many]

Advanced users may wish to add indexes for the expressions that pg_search generates. Unfortunately, the unaccent function supplied by this extension is not indexable (as of PostgreSQL 9.1). Thus, you may want to write your own wrapper function and use it instead. This can be configured by calling the following code, perhaps in an initializer.

PgSearch.unaccent_function = "my_unaccent"

Using tsvector columns

PostgreSQL allows you the ability to search against a column with type tsvector instead of using an expression; this speeds up searching dramatically as it offloads creation of the tsvector that the tsquery is evaluated against.

To use this functionality you'll need to do a few things:

Create a column of type tsvector that you'd like to search against. If you want to search using multiple search methods, for example tsearch and dmetaphone, you'll need a column for each.
Create a trigger function that will update the column(s) using the expression appropriate for that type of search. See: the PostgreSQL documentation for text search triggers
Should you have any pre-existing data in the table, update the newly-created tsvector columns with the expression that your trigger function uses.

Add the option to pg_search_scope, e.g:

pg_search_scope :fast_content_search,
                against: :content,
                using: {
                  dmetaphone: {
                    tsvector_column: 'tsvector_content_dmetaphone'
                  },
                  tsearch: {
                    dictionary: 'english',
                    tsvector_column: 'tsvector_content_tsearch'
                  },
                  trigram: {} # trigram does not use tsvectors
                }

Please note that the :against column is only used when the tsvector_column is not present for the search type.

Combining multiple tsvectors

It's possible to search against more than one tsvector at a time. This could be useful if you want to maintain multiple search scopes but do not want to maintain separate tsvectors for each scope. For example:

pg_search_scope :search_title,
                against: :title,
                using: {
                  tsearch: {
                    tsvector_column: "title_tsvector"
                  }
                }

pg_search_scope :search_body,
                against: :body,
                using: {
                  tsearch: {
                    tsvector_column: "body_tsvector"
                  }
                }

pg_search_scope :search_title_and_body,
                against: [:title, :body],
                using: {
                  tsearch: {
                    tsvector_column: ["title_tsvector", "body_tsvector"]
                  }
                }

Configuring ranking and ordering

:ranked_by (Choosing a ranking algorithm)

By default, pg_search ranks results based on the :tsearch similarity between the searchable text and the query. To use a different ranking algorithm, you can pass a :ranked_by option to pg_search_scope.

pg_search_scope :search_by_tsearch_but_rank_by_trigram,
                against: :title,
                using: [:tsearch],
                ranked_by: ":trigram"

Note that :ranked_by using a String to represent the ranking expression. This allows for more complex possibilities. Strings like ":tsearch", ":trigram", and ":dmetaphone" are automatically expanded into the appropriate SQL expressions.

# Weighted ranking to balance multiple approaches
ranked_by: ":dmetaphone + (0.25 * :trigram)"

# A more complex example, where books.num_pages is an integer column in the table itself
ranked_by: "(books.num_pages * :trigram) + (:tsearch / 2.0)"

:order_within_rank (Breaking ties)

PostgreSQL does not guarantee a consistent order when multiple records have the same value in the ORDER BY clause. This can cause trouble with pagination. Imagine a case where 12 records all have the same ranking value. If you use a pagination library such as kaminari or will_paginate to return results in pages of 10, then you would expect to see 10 of the records on page 1, and the remaining 2 records at the top of the next page, ahead of lower-ranked results.

But since there is no consistent ordering, PostgreSQL might choose to rearrange the order of those 12 records between different SQL statements. You might end up getting some of the same records from page 1 on page 2 as well, and likewise there may be records that don't show up at all.

pg_search fixes this problem by adding a second expression to the ORDER BY clause, after the :ranked_by expression explained above. By default, the tiebreaker order is ascending by id.

ORDER BY [complicated :ranked_by expression...], id ASC

This might not be desirable for your application, especially if you do not want old records to outrank new records. By passing an :order_within_rank, you can specify an alternate tiebreaker expression. A common example would be descending by updated_at, to rank the most recently updated records first.

pg_search_scope :search_and_break_ties_by_latest_update,
                against: [:title, :content],
                order_within_rank: "blog_posts.updated_at DESC"

PgSearch#pg_search_rank (Reading a record's rank as a Float)

It may be useful or interesting to see the rank of a particular record. This can be helpful for debugging why one record outranks another. You could also use it to show some sort of relevancy value to end users of an application.

To retrieve the rank, call .with_pg_search_rank on a scope, and then call .pg_search_rank on a returned record.

shirt_brands = ShirtBrand.search_by_name("Penguin").with_pg_search_rank
shirt_brands[0].pg_search_rank #=> 0.0759909
shirt_brands[1].pg_search_rank #=> 0.0607927

Search rank and chained scopes

Each PgSearch scope generates a named subquery for the search rank. If you chain multiple scopes then PgSearch will generate a ranking query for each scope, so the ranking queries must have unique names. If you need to reference the ranking query (e.g. in a GROUP BY clause) you can regenerate the subquery name with the PgScope::Configuration.alias method by passing the name of the queried table.

shirt_brands = ShirtBrand.search_by_name("Penguin")
  .joins(:shirt_sizes)
  .group("shirt_brands.id, #{PgSearch::Configuration.alias('shirt_brands')}.rank")

ATTRIBUTIONS

PgSearch would not have been possible without inspiration from texticle (now renamed textacular). Thanks to Aaron Patterson for the original version and to Casebook PBC (https://www.casebook.net) for gifting the community with it!

CONTRIBUTIONS AND FEEDBACK

Please read our CONTRIBUTING guide.

We also have a Google Group for discussing pg_search and other Casebook PBC open source projects.

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