# Building Relationship between Models

**URL:** <https://discuss.rubyonrails.org/t/building-relationship-between-models/40519>\
**Category:** rubyonrails-talk\
**Created:** [March 17, 2009, 8:50am UTC](https://discuss.rubyonrails.org/t/building-relationship-between-models/40519 "2009-03-17T08:50:29Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Colin\_Law1](https://avatars.discourse-cdn.com/v4/letter/c/91b2a8/32.png) [@Colin\_Law1](https://discuss.rubyonrails.org/u/Colin_Law1)\
**Post date:** [March 17, 2009, 8:50am UTC](https://discuss.rubyonrails.org/t/building-relationship-between-models/40519/1 "2009-03-17T08:50:29Z")

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> Hi again… 🙂
> 
> I’m still working on RoR
> 
> right now i’m fighting against relationship.
> 
> I generated 3 scaffolds
> 
> car
> 
> wheel
> 
> engine
> 
> all the 3 CRUD works and now in the database I’ve many engines , many
> 
> wheel and many cars.
> 
> I want to correlate this object but how do it ?
> 
> I must say that car has\_one engine and engine belongs\_to car
> 
> (every car can have only one engine)
> 
> or i must write that engine has\_many cars and car belongs\_to engine
> 
> (one engine is used on many different car)
> 
> or I need to create a new scaffold like road\_ready\_car which has\_one
> 
> engine , has\_one car and has\_many wheels

It all depends what you want in the database. Are the cars in the database individual cars, or types of car? If types of car then maybe the name is wrong. Similarly are the engines actual engines or just types of engines? The same for wheels.

If they are all actual individual items then a car has only one engine and an engine has only one car (at any one time at least). A car has 4 wheels (5 including spare?) so car has many wheels, wheel belongs to car.

If, however you are talking about types of cars and engines then a car type may have many engine types and an engine type may have many car types. Perhaps in this case you then need another table for the actual cars where a car is of one car type, one engine type and one wheel type.