[英]Rails N + 1 query problem when fetching associated records with where condition
我有下表结构。 这只是一个例子
UserPost => user_id, post_id, Post, Comment
因此,如果我尝试使用以下查询获取所有user_posts
并在comments
表上执行位置,那么它会触发对comments
表的查询
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,这是预期的行为还是我做错了什么?
如何防止对每个user_post
的查询
您可以做的是在您的 model 中添加另一个has_many
,并使用您想要的过滤器。
# You can name this anything you want but a descriptive name helps
has_many :special_comments, -> { where(visibility: true).order(..) }, class_name: 'Comment'
...并在您的查询中急切加载,这将急切加载两种类型的评论。 这不可避免地会导致一个额外的查询,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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