What exactly is Arel in Rails 3.0? It’s an object model for an algebra of relational query operators. I understand that it is a replacement for ActiveRecord No, it isn’t. It’s a replacement for hand-crafting SQL queries in strings. It is a common query layer that underlies ActiveRecord, but it can also be used as … Read more
This is how you perform a like query in arel: users = User.arel_table User.where(users[:name].matches(“%#{user_name}%”)) PS: users = User.arel_table query_string = “%#{params[query]}%” param_matches_string = ->(param){ users[param].matches(query_string) } User.where(param_matches_string.(:name)\ .or(param_matches_string.(:description)))
If you want to combine using AND (intersection), use merge: first_name_relation.merge(last_name_relation) If you want to combine using OR (union), use or†: first_name_relation.or(last_name_relation) † Only in ActiveRecord 5+; for 4.2 install the where-or backport.
Update 4 – Rails 6.1 Thanks to Tim Park for pointing out that in the upcoming 6.1 you can do this: Person.where.missing(:contacts) Thanks to the post he linked to too. Update 3 – Rails 5 Thanks to @Anson for the excellent Rails 5 solution (give him some +1s for his answer below), you can use … Read more
Rails 4+ ActiveRecord 4.0 and above adds where.not so you can do this: Foo.includes(:bar).where.not(‘bars.id’ => nil) Foo.includes(:bar).where.not(bars: { id: nil }) When working with scopes between tables, I prefer to leverage merge so that I can use existing scopes more easily. Foo.includes(:bar).merge(Bar.where.not(id: nil)) Also, since includes does not always choose a join strategy, you should … Read more