Ruby on Rails：在has_many：through和has_many之间进行选择

Question

I'm trying to create a linkedin clone, in which users can have several skills. They can also have descriptions for each skill and choose whether the skill is their primary skill or secondary skill (they can have only one of each).

I can't decide whether to just use a has_many or has_many :through.

If I use has_many

class Skill < ActiveRecord::Base
    belongs_to :user

    validates :description, presence: true
    validates :name, presence: true
end

class User < ActiveRecord::Base
    has_many :skills, dependent: :destroy
end

Skills table will also have columns primary and secondary, which are booleans.

---

If I use has_many :through

class Skill < ActiveRecord::Base
    has_many :users, through: :users_skills
    has_many :users_skills
end

class UsersSkill < ActiveRecord::Base
    belongs_to :user
    belongs_to :skill
end

class User < ActiveRecord:Base
    has_many :skills, through: :users_skills
    has_many :users_skills
end

Here, I will have the primary and secondary boolean columns in the UsersSkill model.

Which do you think would be a better choice?

Answer 1

Based on both your stated requirements:

I mainly want people to be able to type in a skill to search for people with that skill

They can also have descriptions for each skill and choose whether the skill is their primary skill or secondary skill (they can have only one of each).

And on just my understanding of the meaning of the models, ie that a "Skill" is something which doesn't necessarily belong to a single user -- I'd go with has_many :through.

Reason for this is that the skills are things that stand on their own (and as you said, you want to be able to search for them). Just because one person lists, say, "Scrubbing Floors" as their primary skill, and another as their secondary skill, doesn't mean you should have two entries with "Scrubbing Floors". Have a single Skill for it, and use UsersSkills to assign it to multiple users, along with any information specific to that user's instance of the skill.

You can put the primary/secondary ranking on the users_skills table. The existence of this model will also save you a lot of effort in the future should you ever need to expand the information stored in these mappings.

Answer 2

The bottom line is that the choice depends on one piece of functionality of your system - whether a users' skills are specific to them, or part of a wider group

• The has_many relationship will be good if your user will add their skills themselves
• The has_many :through relationship will be good if your user's skills can be selected from a wider pool

--

System

You have to remember that since Rails is object-orientated , the setup of your ActiveRecord associations is primarily based on the association of the objects in your system.

many-to-many associations are primarily based on the sharing of objects between two models; whilst one-to-many associations are the result of a model having lots of dependent data

To make the decision, I would simply look at what you've got. If you want to pre-populate the skills, as per the likes of LinkedIn, go for the has_many :through