Add Specify Dependencies For A Rake Task as a Ruby TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1211 TILs and counting..._
+_1212 TILs and counting..._
 
 ---
 
@@ -1028,6 +1028,7 @@ _1211 TILs and counting..._
 - [Silence The Output Of A Ruby Statement In Pry](ruby/silence-the-output-of-a-ruby-statement-in-pry.md)
 - [Single And Double Quoted String Notation](ruby/single-and-double-quoted-string-notation.md)
 - [Skip Specific CVEs When Auditing Your Bundle](ruby/skip-specific-cves-when-auditing-your-bundle.md)
+- [Specify Dependencies For A Rake Task](ruby/specify-dependencies-for-a-rake-task.md)
 - [Squeeze Out The Extra Space](ruby/squeeze-out-the-extra-space.md)
 - [String Interpolation With Instance Variables](ruby/string-interpolation-with-instance-variables.md)
 - [Summing Collections](ruby/summing-collections.md)

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

@@ -0,0 +1,37 @@
+# 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.
+
+```ruby
+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.
+
+```ruby
+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.
+
+```ruby
+task top_selling_books: [:download_latest_book_sales_csv, :clean_csv] do
+  # read in CSV and process for top selling books
+end
+```
+
+[source](https://subscription.packtpub.com/book/hardware_and_creative/9781783280773/1/ch01lvl1sec13/task-dependencies-prerequisites)