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Type:
Bug
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Resolution: Done
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Priority:
Minor - P4
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Affects Version/s: 5.1.4
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Component/s: Query
A criteria with eager loading like
Blog.includes(:posts, :highlighted_post => :author)
will eagerly load all the authors for each post in `posts` despite only requesting the author of `highlighted_post`.
Concretely, given the models
class Blog has_and_belongs_to_many :posts belongs_to :highlighted_post, class_name: "Post" end class Post belongs_to :author end class Author end
and seed data
Blog.create(
posts: [
Post.create(author: Author.create),
Post.create(author: Author.create),
Post.create(author: Author.create),
],
highlighted_post: Post.create(author: Author.create)
)
the code
Blog.includes(:posts, :highlighted_post => author)
generates the queries
db.find | STARTED | {"find"=>"blogs", "filter"=>{}}
db.find | SUCCEEDED | 0.000409s
db.find | STARTED | {"find"=>"posts", "filter"=>{"_id"=>{"$in"=>[BSON::ObjectId('57d4c58e3e9d19784e191080'), BSON::ObjectId('57d4c5913e9d19784e191081'), BSON::ObjectId('57d4c5953e9d19784e191082')]}}}
db.find | SUCCEEDED | 0.00045s
db.find | STARTED | {"find"=>"posts", "filter"=>{"_id"=>{"$in"=>[BSON::ObjectId('57d4c99a3e9d19784e191085')]}}}
db.find | SUCCEEDED | 0.000678s
db.find | STARTED | {"find"=>"authors", "filter"=>{"_id"=>{"$in"=>[BSON::ObjectId('51393dad509f9f4db7000007'), BSON::ObjectId('513945663684a9dbb0000002'), BSON::ObjectId('51c911dc961afd96a9000009'), BSON::ObjectId('5205b3f4cc75585db3000007')]}}}
db.find | SUCCEEDED | 0.003761s
which tries to load all 4 authors in the seed data, rather than just the one belonging to `highlighted_post`.