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Kevin Korte
Kevin Korte
28,148 Points

Need help building my Active Record schema

So I need help building out my schema for a rails app.

In one table, I'll store parts. I am considering using Single Table Inheritance here, since for parts I could have oil filters, air filters, spark plugs, etc, all which would have a brand, part_number, and type.

I'd also have a table of machines, most likely a title like Year Make Model.

Each part has many machines, and each machine has many parts. It would seem I would want to use a has many through relationship with a join table.

On the view, I need to be able to separate out the parts based on their type. So loop through and grab all air filters that are associated with that machine, than loop through and grab all oil filters etc.

I initially thought I wanted an array of part_id numbers for each type stored with the machine in the machine table, but that seems frowned upon.

Am I on the right track designing my schema? If all goes well, this would hold 10's of thousands of parts, and thousands of machines, and I need an easy way to tie a part number to a machine.

Reverse search would also be a feature I would want to look at; giving the user the option to enter a part number, and get a list of all machines that it is associated with.

1 Answer

Artem Prytkov
Artem Prytkov
11,932 Points

I think your idea is generally right: just dont forget to make indexes on bridge table and use "include" method in ActiveRecord in order to avoid n+1 queries. Not so sure about STI - its useful when you have models with same data but different methods? but in your case all objects in table should be same. It might be better to extract third table PartType where you will store types. This way you can easily get your part details with query like

PartType.where(type: "filter").parts
Kevin Korte
Kevin Korte
28,148 Points

Thanks for that. I got it working today, using has_many through and I have a fitments table that is joining parts and machines together. I went this route because I believe I'll also be able to store a position integer and control the views output. I'm able to add and remove relationships in the console, so all is good so far.

I created a migration, and added my index column on my fitments table. My migration is basic, and looks like this:

class AddIndexToFitment < ActiveRecord::Migration
  def change
    add_index :fitments, :part_id
    add_index :fitments, :machine_id

Here is my question, I'm still learning how this works, but is Rails smart enough to populate these columns for the data that was existing before the migration, and I assume it will populate the index's going forward. Is there anything more I have to do in my model or controller? And is it normal that I can't find these indexs in the console? I just wanted to see if they had values or not.

Appreciate the help.