Lets say we are trying to define a relationship user and product in ActiveRecord you need to :-
1. Define association on both sides of your model. For example, a user can have many products, you would in turn define relationship as follows :-
We have the association parameter on both sides of our model. This also means product table will need a column called 'user_id'- which stores relationship to a specific user who owns this product.
User model has a marker called 'has_many'
Product model has a marker called 'belongs_to' - belongs_to also requires that you create a new column called user_id field in your database.
Please note, that i use 'Product' and not the plural table name auto created by rails which always pluralized an object for you.
2. create a new database migration - it might involve creation of a new field for example user_id to hold data for an association. We might run the following command
rails generate migration add_user_id_to_product user_id :string
3. run rake db:migration
4. Use rails console to test out this association