Today I was creating a model method which would return some associated objects. It wasn’t hugely complex but I basically needed to match an sql string which looked something like this:

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 SELECT * FROM table WHERE column_one = something AND column_two = something
 OR column_three = something AND column_four = something

After reading some arel documentation, I came up this:

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 version  = Version.arel_table
 versions = Version.where(version[:c1].eq(something).and(version[:c2].eq
 (something)).or(version[:c3].eq(something).and(version[:c4].eq(something))))

If this is a bit too fiddly for you then there are some nice gems that do this for you, such as Squeel.