[英]Rails N + 1 query problem when fetching associated records with where condition
我有下表結構。 這只是一個例子
UserPost => user_id, post_id, Post, Comment
因此,如果我嘗試使用以下查詢獲取所有user_posts
並在comments
表上執行位置,那么它會觸發對comments
表的查詢
user_posts = UserPost.includes(post: :comments)
user_posts.each do |up|
post = up.post # No Query
comments = up.comments # No query
comments_with_condition = up.comments.where(visibility: true).order(position: :asc).first.data # Fires query for .where and .order as well.
end
那么,這是預期的行為還是我做錯了什么?
如何防止對每個user_post
的查詢
您可以做的是在您的 model 中添加另一個has_many
,並使用您想要的過濾器。
# You can name this anything you want but a descriptive name helps
has_many :special_comments, -> { where(visibility: true).order(..) }, class_name: 'Comment'
...並在您的查詢中急切加載,這將急切加載兩種類型的評論。 這不可避免地會導致一個額外的查詢,但它不是N+1。
user_post = UserPost.includes(post: [:comments, :special_comments])
user_posts.each do |user_post|
post = user_post.post
comments = user_post.comments
comments_with_condition = user_post.special_comments
end
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