Question

I am trying to retrieve a child object based on the key in its parent’s table. For instance, I have the Customer class which contains a “store_id” key to the Stores tables. If a customer has a “store_id” key, I would like to bring back that Store object and not the parent Customer object.

EDIT: Here is a sql statement showing what I am trying to do.

So the SQL statement would look something like this.

“SELECT storeS.* FROM customers INNER JOIN stores ON customers.store_id = storeS.id WHERE customers.id = ‘9’”

I know the sql is probably wrong, but thats a very concise way to show it.

Answer 1

I am assuming you are using rails with the out-of-the-box configuration (using ActiveRecord).

By convention, the “store_id” key in the “customers” table should match an “id” field in the “stores” table. You should also have the following class models setup:

class Store < ActiveRecord::Base
  has_many :customers # this is not required for what you want to do here, but recommended
end

class Customer < ActiveRecord::Base
  belongs_to :store
end

Assuming this is true, you can either do this if you have the store key:

# assuming we have store key == 9
Store.find(key)

Or you could do this if you already have the customer:

# assuming we have customer.store_id == 9
customer.store

Or if you only have the customer key:

# assuming we have a customer key == 9
customer = Customer.find(9)
store = customer.store