如何在Rails数组中传递MySQL where IN条件

Question

I have on array like below,

 skills = ['ruby','Ruby on Rails'];

I am trying to pass array in mysql where condition like below

 questions =  MysqlConnection.connection.select_all("
                   SELECT questions.*,quest_answers.* FROM `questions` 
                   INNER JOIN `quest_answers` ON `quest_answers`.`question_id` = 
                  `questions`.`id` where questions.category IN (#{skills.join(', ')})")

But it did not work,How can pass an array to where In condition.

Error I am getting

  Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'on rails,  Ruby)' at line 1:  SELECT questions.*,quest_answers.* FROM `questions` INNER JOIN `quest_answers` ON `quest_answers`.`question_id` = `questions`.`id` where questions.category IN (Ruby on rails,  Ruby)

Answer 1

You are passing a string representation of the array to MySQL, which doesn't work. You need to insert the values in the array into the query. This can be done by escaping the skills, and joining them:

skills.map { |s| "'#{s}'" }.join(', ')

This produces 'ruby', 'Ruby on Rails' , which is a valid argument for the IN statement.

A better approach however is to not write the raw SQL at all, but rely on ActiveRecord to generate it. This is the more maintainable and readable approach.

Question.joins(:quest_answers).where(category: skills)

Passing an array to where converts it automatically into a subset condition .