Ruby on Rails和渴望加载模型关联（包括或不包括）？

Question

So perhaps this is a dumb question, but I've been reading the the rails guide on the model associations and am trying to figure out if I need to use an include or not.

So if I have a model for article and an article has_many comments, the comments are eager loaded. However, if I'm frequently accessing the author of the comment from the article model I would need to use an :include to eager load it. This makes sense to me.

However, what happens if I call a model method like @article.comments.author_named_sam? which uses the author.

Would placing an include in the article model to ensure author is eager loaded mean that when this method is called and in turn queries the author, that this is using the eager loaded author?

Answer 1

if the include is specified for author then the author object will be used from loaded objects only when it called from comment object using association(standard rails way).

like following;

def author_named_sam?
  author.name == 'sam' 
end

You can try by following code and analyze the queries made to database from console

Article.includes(comments: [:author]).find(1) 

Answer 2

In my opinion, using eager loading in associations often is not a good idea, because it easily can become problematic for performance.

It's better practice, in my opinion, explicitly eager-load association only when you need them. I mean using :includes during querying.

For instance, query like this:

Article.includes(comments: :author)

will load comments and author objects along with articles. Thus avoiding N+1 queries and not forcing you to make artificial decisions in designing your models.

http://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations

There are some caveats with includes method though. See this excellent post on more details about includes and other related methods.