specify-dependencies-for-a-rake-task.md

Specify Dependencies For A Rake Task

Let's say you have rake task that performs some important business task. For instance, a book seller might want a task that can tell them the top selling books from a CSV report.

task :top_selling_books do
  # read in CSV and process for top selling books
end

This works great if the CSV file already exists on the machine from which this task is run. What if it isn't tho?

The CSV is a prerequesite for this task. We explicitly define it as a prerequisite using the task dependency syntax.

task :download_latest_book_sales_csv do
  # saves a CSV of book sales
end

task top_selling_books: :download_latest_book_sales_csv do
  # read in CSV and process for top selling books
end

We can even define multiple task dependencies with an array.

task top_selling_books: [:download_latest_book_sales_csv, :clean_csv] do
  # read in CSV and process for top selling books
end

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