Just enough fundamentals to be fluent preloading associations with ActiveRecord, and start helping your team to avoid n+1 queries on production.
Master n+1 queries identification, preloading, counts and counter caches, and eliminate n+1 queries from your code.
Imagine that you want to truncate a filename, but you want to keep showing the extension of the file. Like “A big file name that…awesome.pdf”. How would you do it?