These are some key takeaways from the 3rd course for me based on the curriculum as well as the feedback received from the TAs for every module (aka Week).

• self-referential associations (a user following another user)
• ActionMailer: sending emails
• token generation for password reseting

Module 4

• Avoid rendering from a POST request unless there’s an error.
• Try to keep the test setup close to the action and assertion (double check the use of let and before after writing specs). This helps in readability of the specs.
• Single-Assertion Principle (more of a guideline than a law): Avoid unrelated assertions in a single spec.
• Name the shared_examples well enough to be understood clearly.
• Use flash.now["alert message"] for rendering instead of flash["alert message"]. The latter carries over to the next request which is why it is used with redirect_to - a new request.

• Use pluck instead of map for performance. pluck pulls only the ids from the database and loads the data into an array. It saves a lot of processing time and power over loading every record into memory using map. However, here’s an article that talks about when pluck is unnecessary.
• For efficient single-record search, use find_by(attribute: value) than the fancy find_by_attribute(value), which goes through method_missing, and doesn’t even save much typing!
• Avoid writing migrations for populating data. Write a custom rake task under ‘lib/tasks’ instead.
• Clear ActionMailer deliveries using ActionMailer::Base.deliveries.clear in before or after hooks instead of in a particular spec to ensure their purging.

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