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sqlruby-on-railsrubypostgresqlrake

How do I write this ruby rake task in straight postgresql?

Here is the rake task:

task :map_comment_to_user => :environment do
    Comment.all.each do |c|
      a         = Admin.where(mongo_id: c.mongo_user_id).first
      u         = User.where(email: a.email).first
      c.user_id = u.id
      c.save
    end
  end

I screwed up a migration from Admin => User tables, and the email being unique allows me to stitch them back together. But it's so slow.

How do I write the above in straight PSQL?

UPDATE comments c 
SET c.user_id = u.id 
FROM users u admins a 
WHERE c.mongo_user_id == a.mongo_id 
  AND u.email = a.email; ???
Solution

  • Your SQL is very close. It just require a few minor syntax changes.

    UPDATE comments c
SET user_id = u.id
FROM users u, admins a
WHERE c.mongo_user_id = a.mongo_id
  AND u.email = a.email;