How to execute build_association if association is saved in a string?

Question

In Rails has_one relationship, if the association name is stored in a string, how to build the child object whose name is saved in a string?

For example, a customer has_one address :

class Customer < ActiveRecord::Base
   has_one :address
end

We can do:

customer = Customer.new
address = customer.build_address

If the association is saved in a variable name @association , How can we create address with the variable @association ?:

@association = 'address'
customer = Customer.new
address = customer.build_{@association}  #code does not work.

We tried customer.build_"#{@association}" & 'customer.build_#{@association} and none of them worked.

Answer 1

You want to do meta-programming, ie here, calling a method whose name is contained in a variable.

The Ruby method you need to use is send :

customer.send("build_#{association_name}")

You can only use the #{...} syntax in double quoted strings ".." OR regex /../

Note that send also work with symbols, and you can supply parameters after the first one. Remember that =, [], !, ? are also part of the method name.

method= 'name=', 
new_name= "hello"
@your_object.send(method, new_name)