Ruby on Rails Associations - Practical Applications

Hey All, Forgive me for posting a question that may be very elementary.

I'm building an application and am a bit stuck on how to work out the associations. It goes like this:

User :has_many vehicles User :has_many logs

Vehicle :has_many logs

User -> Vehicles -> Logs

The Vehicles have a user_id attribute. The Logs have user_id and vehicle_id attributes.

I am using restful authentication and am able to associate the vehicles with the users al a

Cam wrote:

Hey All, Forgive me for posting a question that may be very elementary.

I'm building an application and am a bit stuck on how to work out the associations. It goes like this:

User :has_many vehicles User :has_many logs

Vehicle :has_many logs

User -> Vehicles -> Logs

The Vehicles have a user_id attribute. The Logs have user_id and vehicle_id attributes.

I am using restful authentication and am able to associate the vehicles with the users al a ----- def create     @vehicle = current_user.vehicle.build (params[:vehicle]) ...... ------

I can't figure out how I should do it for the log. Thanks again, and sorry for my lack of understanding of how rails works.

Cheers,

Cam Peterson

In User model write has_many :logs has_many :vehicles

In Vehicle model write has_many :logs

In your logs model write belongs_to :user belongs_to :vehicle

In your vehicle model write belongs_to :user

def create      @vehicle = current_user.vehicle.create (params[:vehicle])

Cam wrote:

Hey All, Forgive me for posting a question that may be very elementary.

I'm building an application and am a bit stuck on how to work out the associations. It goes like this:

User :has_many vehicles User :has_many logs

Vehicle :has_many logs

User -> Vehicles -> Logs

The Vehicles have a user_id attribute. The Logs have user_id and vehicle_id attributes.

I am using restful authentication and am able to associate the vehicles with the users al a ----- def create     @vehicle = current_user.vehicle.build (params[:vehicle]) ...... ------

I can't figure out how I should do it for the log. Thanks again, and sorry for my lack of understanding of how rails works.

You probably want to use has_many :through. Have you read the Rails guide on associations?

Cheers,

Cam Peterson

Best,

Cam wrote:

I'm building an application and am a bit stuck on how to work out the associations. It goes like this:

User :has_many vehicles User :has_many logs

Vehicle :has_many logs

User -> Vehicles -> Logs

The Vehicles have a user_id attribute. The Logs have user_id and vehicle_id attributes.

I see two possible scenarios here. Neither is wrong, They depend on behavior you want.

1. Users have many vehicles and vehicles have many logs. 2. Users have many vehicles through logs.

In scenario (1) you would need two one-to-many associations:

User   has_many :vehicles

Vehicle   belongs_to :user   has_many :logs

Log   belongs_to :user

Logs would now indirectly belong to a user because vehicles belong to users. Therefore Log would have only a foreign key to vehicle, but no foreign key to user since that would be redundant.

Find the User for a Log with: user = my_log.vehicle.user

In scenario (2) there would be a many-to-many association between User and Vehicle with Log joining them.

User   has_many :logs   has_many :vehicles, :through => :logs

Vehicle:   has_many :logs   has_many :users, :through => :logs

Log   belongs_to :user   belongs_to :vehicle

This scenario could be read as Users have many vehicles and vehicles can belong to many users, where logs track the association and can store information pertaining to a specific vehicle belonging to a specific user.

I'm guessing this is not the scenario you want, but this pattern certainly has its uses.