rails Eager loading
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若存在如下Post model:
使用下面的循环加载数据时产生了N+1查询问题:
Post.all.each do |post| puts "Post: " + post.title puts "Written by: " + post.author.name puts "Last comment on: " + post.comments.first.created_onend
首先,解决author获取问题:
Post.includes(:author).each do |post|
然后解决comments加载:
Post.includes(:author, :comments).each do |post|
带条件的eager loading:
Post.includes([:author, :comments]).where(['comments.approved = ?', true]).all
多态关系的eager laoding
Address.includes(:addressable)
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