Creating or updating a has_one ActiveRecord association

Question

I've been trying to get my head around ActiveRecord associations but I have hit a bit of a brick wall, and no matter how much I review the ActiveRecord documentation, I can't work out how to solve my problem.

I have two classes:

Property -> has_one :contract   Contract -> belongs_to :property 

In my contract class, I have a method to create_or_update_from_xml

First I check to make sure the property in question exists.

property_unique_id = xml_node.css('property_id').text       property = Property.find_by_unique_id(property_unique_id)       next unless property 

And this is where I get stuck, I have a hash of attributes for the contract, and what I want to do is something like:

if property.contract.nil?   # create a new one and populate it with attributes else   # use the existing one and update it with attributes 

I know how I would go about it if it was raw SQL, but I can't get my head around hte ActiveRecord approach.

Any hints past this road block would be hugely appreciated.

Thanks in advance.

Answer 1

if property.contract.nil?   property.create_contract(some_attributes) else   property.contract.update_attributes(some_attributes) end 

Should do the trick. When you have a has_one or belongs_to association then you get build_foo and create_foo methods (which are like Foo.new and Foo.create). If the association already exists then property.contract is basically just a normal active record object.

Answer 2

Just another way of doing it using ruby OR-Equal trick

property.contract ||= property.build_contract property.contract.update_attributes(some_attributes) 

Update:

@KayWu is right, the above ||= trick will create the contract object in the first line, rather than just building it. An alternative would be

property.build_contract unless property.contract property.contract.update_attributes(some_attributes)