Rails array alternative to has_and_belongs_to_many

We have the Post model and Post model can have many categories. The classic way is to implement has_and_belongs_to_many association and two additional tables. If you need some advanced functionality then you should go with has_many through association. But if you need just to save several categories for the post we will do the alternative way: through one array column in posts table. Ok let us start. Migration:

add_column :posts, :category_ids, :text, array: true, default: []

Very often we need to store some seed data. In our case we should store the list of categories and this data will never be updated. I prefer to use the localizations for that. Yaml files has [lists(https://en.wikipedia.org/wiki/YAML) en.yml:

en:
  posts:
		categories:
			- Tools
			- Services
			- Other

Now you can get the list of categories by calling I18n.t('posts.categories'). In our database we will save array with indexes of values. Add next code to your form:

 I18n.t('posts.categories').each_with_index do |category, i|
    = checkbox_tag 'post[categories][]', i, f.object.categories.include?(i.to_s), id: "category_#{i}"
		= label_tag "category_#{index}", category