activerecord-import implements AR#import activerecord-import is a library for bulk inserting data using ActiveRecord. see how it works: books = [] 10.times do |i| books << Book.new(:name => “book #{i}”) end Book.import books Project’s home is on Github and it’s wiki.
Rails now does this by default 🙂 Message.where(user_id: Profile.select(“user_id”).where(gender: ‘m’)) will produce the following SQL SELECT “messages”.* FROM “messages” WHERE “messages”.”user_id” IN (SELECT user_id FROM “profiles” WHERE “profiles”.”gender” = ‘m’) (the version number that “now” refers to is most likely 3.2)
ActiveRecord queries are ActiveRecord::Relation objects (which maddeningly do not support or), not Arel objects (which do). [ UPDATE: as of Rails 5, “or” is supported in ActiveRecord::Relation; see https://stackoverflow.com/a/33248299/190135 ] But luckily, their where method accepts ARel query objects. So if User < ActiveRecord::Base… users = User.arel_table query = User.where(users[:kind].eq(‘admin’).or(users[:kind].eq(‘author’))) query.to_sql now shows the reassuring: … Read more
Use the key word WITH once at the top. If any of your Common Table Expressions (CTE) are recursive (rCTE) you have to add the keyword RECURSIVE at the top once also, even if not all CTEs are recursive: WITH RECURSIVE cte1 AS (…) — can still be non-recursive , cte2 AS (SELECT … UNION … 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
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.
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)))
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