Just like houses need a strong foundation, an app needs a strong foundation to work well. For a while, I thought that I had functional understanding of how to set up ActiveRecord Associations (especially many-to-many relations), but it wasn’t until I started to explain to relationships in my Rails Portfolio App that I fully realize that something wasn’t clicking. I had to take a few steps back and read, write, practice, and verbalize (my mantra). In this post I will focus on the has_many through: !
Associations
The simplest way to define this concept is that an association is a connection between two Active Record models. These relations help to make operations like creating a new post to an existing author object easier. Let’s look at an example of an app without associations:
If we want to add a post to an existing user we have to do this (kind of annoying):
When we take advantage of the Active Record Associations we declared a connection between the models, and do more operations like create, destroy, update, etc more simpler, and faster!!
Many-to-many relations: has_many :through
There are six types of association, but I want to focus in one, the one that I’ve been struggling a little with : has_many :through . From the Rails Guide we get this information:
has_many :through association is often used to set up a many-to-many connection with another model. This association indicates that the declaring model can be matched with zero or more instances of another model by proceeding through a third model.
I remember reading it a couple of weeks ago and thinking that it was cool. But today, I read two or three times, and it finally click on my brain. I had to practice by creating a simple diagram and an app. For the practice/example I thought about teachers, students, and parents:
With this association you can use the same has_many methods and create join models (e.g. teacher.parents = parents )
My lesson
No matter how simple is the concept, always review and practice it. I struggle with this a bit in my Rails project, but I’m glad that it happened because it gave another chance to review and finally get a grasp of it! Now that I understand it a little better, I will continue on improving, and fixing the associations of this project for the Javascript section.