N.B. Context records have been deprecated. Please use contextual filters instead.

Configuring a context record allows you to scope a report to only include data associated with a single record.

For example, let's say that we have a Blog model that has_many :posts, and on each blogs#show view, we want to show a chart of the number of posts by author for that specific blog.

Here's our model:

class Blog < ApplicationRecord
  has_many :posts
end

A report that counts Posts by author would look like this:

measure: post
dimensions:
- author

But it would count all posts, and not be scoped to a specific Blog record. It would perform a query similar to Post.group(:author_id).count, but we want @blog.posts.group(:author_id).count.

To do this, we would include the blog ID in render_report's context_params:

# app/views/blogs/show.html.haml

= render_report 'my_posts', context_params: { blog_id: @blog.id }

And we would configure ReportsKit to set the appropriate context record when that parameter exists:

# config/initializers/reports_kit.rb

ReportsKit.configure do |config|
  config.context_record_method = lambda do |controller|
    context_params = controller.params[:context_params]
    return unless context_params && context_params[:blog_id].present?
    Blog.find(context_params[:blog_id])
  end
end

The above method is called during the API request to generate the data for the report.

Now, the report in that view will essentially show Blog.find(context_params[:blog_id]).posts.group(:author_id).count, as we wanted.

If we use the same report in another view and we don't pass context_params to render_report, then context_record_method will return nil, and the report will show the data for all posts (Post.group(:author_id).count), as it did before.