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Editorial Team
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Asked: 2026-06-17T16:45:25+00:00

What’s the best way to implement an atomic insert/update for a model with a

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What’s the best way to implement an atomic insert/update for a model with a counter in Rails? A good analogy for the problem I’m trying to solve is a “like” counter with two fields: 

url   : string
count : integer

Upon insert, if there is not currently a record with a matching url, a new record should be created with count 1; else the existing record’s count field should be incremented.

Initially I tried code like the following:

Like.find_or_create_by_url("http://example.com").increment!(:count)

But unsurprisingly, the resulting SQL shows that the SELECT happens outside the UPDATE transaction:

Like Load (0.4ms)  SELECT `likes`.* FROM `likes` WHERE `likes`.`url` = 'http://example.com' LIMIT 1
(0.1ms)  BEGIN
(0.2ms)  UPDATE `likes` SET `count` = 4, `updated_at` = '2013-01-17 19:41:22' WHERE `likes`.`id` = 2
(1.6ms)  COMMIT

Is there a Rails idiom for dealing with this, or do I need to implement this at the SQL level (and thus lose some portability)?

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1 Answer

  1. Editorial Team

    I am not aware of any ActiveRecord method that implemts atomic increments in a single query. Your own answer is a far as you can get.

    So your problem may not be solvable using ActiveRecord. Remember: ActiveRecord is just a mapper to simplify some things, while complicating others. Some problems just solvable by plain SQL queries to the database. You will loose some portability. The example below will work in MySQL, but as far as I know, not on SQLlite and others.

     quoted_url = ActiveRecord::Base.connection.quote(@your_url_here)
::ActiveRecord::Base.connection.execute("INSERT INTO likes SET `count` = 1, url = \"#{quoted_url}\" ON DUPLICATE KEY UPDATE count = count+1;");
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