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Using Named Scopes Across Models with ActiveRecord#Merge Discussion

Chris Oliver asked in General

You have to fix your latest blog Post excerpt on the home page.
Great site btw.

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Doh! I'll get on that. My markdown parser sure didn't like that video.

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Leung Ho Kuen Leung Ho Kuen

I am doing it with subquery
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Author.where(id: Book.available.select(:author_id))

I agree that your version is cleaner and easier to remember,
but you might want to add .distinct after joins to avoid duplicated authors.

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Ah yes, great points! I like that as a subquery and definitely need the distinct for my example as well.

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Văn Lý Vũ Văn Lý Vũ

this query will generate a long SQL query. it's not best practice.

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Well, this is useful, but ugly... Thinking about querying, im not supposed to "merge" anything. IMHO

My wish was Author.books.scope(:available), lol

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Well you can do Author.books.available because that's just querying Book.where(author_id: X).available. But obviously this is for the more complex joining tables case, so at least you're working with the models like you normally would. Not the best, but it saves you from duplication.

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Văn Lý Vũ Văn Lý Vũ

Nice guys.

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Blake Thomson Blake Thomson

Minor nitpick: but I really think you mean `ActiveRecord::Relation#merge`, not `ActiveRecord#merge`

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(Y)

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Something wrong with the video :/

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Fixed!

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godie mendoza godie mendoza

great! is ugly, but useful, thanks!

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bodaonline bodaonline

Big thanks! Had a default scope on my Model but rails 4.2.5 didn't unscope it when I was doing "each do" so using the .joins(:model).merge(Model.scope) you suggested instead

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Nicholas Thompson Nicholas Thompson

Could do something like:

scope :has_available_books, -> { joins(:books).merge(Book.available) }

Then you could just do:

Author.has_available_books

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Konstantin Ivanov Konstantin Ivanov

Need to note that merges on the same attribute overrides each other.

class Book < ActiveRecord::Base
...
scope :red, ->{ where(color: "red") }
scope :green, ->{ where(color: "green") }
end

Author.joins(:books).merge(Book.red).merge(Book.green)
^ would apply only green, because overwrite previous merge

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