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ruby-on-railsactiverecord

ActiveRecord Get Max Value Without Loading

I need to get the last record with a certain value, but without loading it.

I have to do something like:

Thing.where(cool: true).where(created_at: Thing.where(cool: true).maximum(:created_at))

The above is a way to do it, but it does a 2nd query to get the maximum value first. I want to do it all in one query and get the SQL equivalent of something = max(etc).

Just before someone mentions it: .last doesn't work because it returns an object not a relation.

In order words, I need to do .last but returning a relation instead of objects.

Solution

  • Try this way:

    Thing.where("cool=1 AND created_at=(SELECT MAX(created_at) FROM things WHERE cool=1)")

    On Rails 7, when I tested your query, the database is queried only once.