I send an email each week, trying to share knowledge and fixes to common problems and struggles for ruby on rails developers, like How to fetch the latest-N-of-each record or How to test that an specific mail was sent or a Capybara cheatsheet. You can see more examples on Most recent posts or All post by topic.
I want to share with you an example application to help you visualize why “fixing” an n+1 queries problem, can hurt the performance of your application if you preload assocations with too many records.
It simulates the index page of a blog application...
Read moreSometimes people say that “fixing” some n+1 queries could hurt performance…
Maybe this phrase can be confusing, because if you have not been exposed to a lot of n+1 queries problems, it could be hard to imagine how it can be possible.
And also is...
Read moreI want to tell you that I have added a new section to the guide for preloading associations in rails, to introduce you to something I call “Preload objects” that will help you build complex preloads for those cases when you can’t find a way to do what you need to do, with the standard rails mechanisms.
Sometimes just using preload or includes is not possible… or maybe it is, but you just can’t figure it out how to do it.
Maybe you want to preload some records matching two keys, or preload a grouped relation.
Maybe you know how to represent the association with a has_many
:through, but you need something faster, or to use less memory.
In that kind of situations, one thing that you can do is to write a custom object to represent that preload.
Here I will try to explain how and when you can do it with an example.
Maybe you are already familiar with includes or preload, but you know
that a lot of the time you will need more than just preload(:comments).
It is common to have complex nested associations, scopes that you need or want to reuse, places where preloading all the associated records could hurt the performance of your app.
How do you work with complex nested associations?… How do you simplify the preloading of those nested associations?… How do you “preload an scope”?… How do you preload just the latest n of each record?
An n+1 queries problem means that a query is executed for every result of a previous query.
For example, with this records…
class Post < ActiveRecord::Base
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :post
end
If you...
Read moreA common cause of n+1 queries is fetching the “latest-N-of-each” record on a list of records.
Some examples of this problem are trying to get…
There are different practices, that I know, to test that an email was sent in Rails…
If you want to test that an email was sent on a system spec in rails…
What you can do is to check the ActionMailer::Base.deliveries to see if the email that you want is there.
As you may now there are two hard things in computer science and one of them is naming things.
And although naming things is an art, is not bad to have a little guide on how to do it.
That’s why I want to share with you a guide on how to name scopes...
Read more