This course is built on Symfony 2, but most of the concepts apply just fine to newer versions of Symfony. If you have questions, let us know :).
You already know how to query with SQL, so learning how to do complex queries with Doctrine should not give you a headache. In this series, we'll learn the language Doctrine speaks (DQL), as well as the query builder object, how to use complex query features and even how to run good ol' fashioned raw SQL queries with Doctrine. Because hey, sometimes simplicity rules :).