Wharel

Wharel helps you write concise Arel queries with ActiveRecord using Virtual Rows inspired by Sequel.

Although similar in spirit to gems like Squeel and BabySqueel, which provide sophisticated block-based interfaces for querying with Arel, Wharel is much much smaller. In fact, the core of the gem is only 30 lines long! It uses a single BasicObject as a clean room to evaluate the query block. That's really all there is to it.

For a more detailed explanation of the implementation, see this blog post.

Add this line to your application's Gemfile:

gem 'wharel', '~> 1.0.0'

And then execute:

$ bundle

Or install it yourself as:

$ gem install wharel

Suppose we have a model Post:

class Post < ApplicationRecord
  has_many :comments
end

And let's assume our Post has columns title and content.

Now, if we wanted to find all the posts with a title which matched the string "foo" and content which matched the string "bar", we'd have to resort to something like this:

title = Post.arel_table[:title]
content = Post.arel_table[:content]
Post.where(title.matches("foo").and(content.matches("bar")))

With Wharel, you can drop the boilerplate and just use a block:

Post.where { title.matches("foo").and(content.matches("bar")) }

Wharel will map title and content in the block to the appropriate Arel attribute for the column.

Wharel also supports most other query methods, e.g. not:

Post.where.not { title.eq("foo") }

... and order:

Post.order { title.lower }

Wharel also supports select, having, pluck, pick, group and or in the same way.

Now suppose we have another model Comment with a column content, and a Post has_many :comments:

class Post < ApplicationRecord
  has_many :comments
end

class Comment < ApplicationRecord
  belongs_to :post
end

Now we want to find all comments which match the title of the comment's post. With standard Arel, you could do this with:

posts = Post.arel_table
comments = Comment.arel_table
Comment.joins(:post).where(comments[:content].matches(posts[:title]))

Using Wharel, you can pass an argument to blocks to handle this case:

Comment.joins(:post).where { |c| Post.where { |p| c.content.matches(p.title) } }

Much better!

Notice something wrong or a feature missing? Post an issue or create a pull request.

The gem is available as open source under the terms of the MIT License.