Posted almost 5 years ago. Visible to the public. Repeats. Linked content.

How to explain SQL statements via ActiveRecord

ActiveRecord offers an explain method similar to using EXPLAIN SQL statements on the database.

However, this approach will explain all queries for the given scope which may include joins or includes.

Output will resemble your database's EXPLAIN style. For example, it looks like this on MySQL:

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User.where(id: 1).includes(:articles).explain
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EXPLAIN for: SELECT `users`.* FROM `users`  WHERE `users`.`id` = 1 +----+-------------+-------+-------+---------------+ | id | select_type | table | type  | possible_keys | +----+-------------+-------+-------+---------------+ |  1 | SIMPLE      | users | const | PRIMARY       | +----+-------------+-------+-------+---------------+ +---------+---------+-------+------+-------+ | key     | key_len | ref   | rows | Extra | +---------+---------+-------+------+-------+ | PRIMARY | 4       | const |    1 |       | +---------+---------+-------+------+-------+   1 row in set (0.00 sec)   EXPLAIN for: SELECT `articles`.* FROM `articles`  WHERE `articles`.`user_id` IN (1) +----+-------------+----------+------+---------------+ | id | select_type | table    | type | possible_keys | +----+-------------+----------+------+---------------+ |  1 | SIMPLE      | articles | ALL  | NULL          | +----+-------------+----------+------+---------------+ +------+---------+------+------+-------------+ | key  | key_len | ref  | rows | Extra       | +------+---------+------+------+-------------+ | NULL | NULL    | NULL |    1 | Using where | +------+---------+------+------+-------------+   1 row in set (0.00 sec)

By refactoring problematic code and creating automated tests, makandra can vastly improve the maintainability of your Rails application.

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Arne Hartherz
Last edit:
almost 5 years ago
by Besprechungs-PC
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Posted by Arne Hartherz to makandra dev
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