RelationToStruct

When one needs to use ActiveRecord to fetch specific values (whether subset columns of a model or arbitrary calculated columns), it's desirable to avoid the overhead of model instances and any associated callbacks.

ActiveRecord::Relation#pluck solves a similar problem but returns tuples; I wanted to be able to return Ruby structs to benefit from named instance methods.

Installation

Add this line to your application's Gemfile:

gem 'relation_to_struct'

And then execute:

$ bundle

Or install it yourself as:

$ gem install relation_to_struct

Examples

You can query either via direct SQL or from an ActiveRecord relation.

From an existing relation

UserPostsSummary = Struct.new(:user_name, :post_count)
relation = User.joins(:blog_posts).where(name: 'Hayek').group('users.id').select('users.name, COUNT(blog_posts.id)')
relation.to_structs(UserPostsSummary) # => array of structs

From raw SQL

UserPostsSummary = Struct.new(:user_name, :post_count)
sql = <<-eos
  SELECT users.name, COUNT(blog_posts.id)
  FROM users
  LEFT OUTER JOIN blog_posts ON blog_posts.user_id = users.id
  GROUP BY users.id
eos

ActiveRecord::Base.structs_from_sql(UserPostsSummary, sql) # => array of structs
ActiveRecord::Base.pluck_from_sql(sql) # => array of tuples

sql = <<-eos
  SELECT users.name
  FROM users
  LIMIT 1
eos

ActiveRecord::Base.value_from_sql(sql) # => single value

sql = <<-eos
  SELECT users.id, users.name
  FROM users
  LIMIT 1
eos

ActiveRecord::Base.tuple_from_sql(sql) # => [id, name]

Contributing

1. Fork it ( https://github.com/jcoleman/relation_to_struct/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Test your changes (bundle install && appraisal install && rake)
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create a new Pull Request