ruby on rails - How to create links between two tables -

ok i'm starting on normalising database. have 1 model "products" populated 60,000 products via data feed (xml), contains product category name , merchant name. want split these 3 models; products, categories , merchants.

each product has 1 category , 1 merchant natural idea create these models:

category_id | category_name

merchant_id | merchant_name

i can work out code associate between models i.e. has_one, belongs_to etc i'm struggling work out automatically associate new product category , merchant programatically.

i've seen examples in books start empty database , seems pretty straightforward. however, i'm starting off full database , list of category names.

here product creation statement working great:

product.create(:name => node.xpath("./text/name/text()").inner_text.downcase,                     :description => node.xpath("./text/desc/text()").inner_text,                    :brand => node.xpath("./brand/text()").inner_text,                    :merchant => node.xpath("../@name").inner_text,                    :category => node.xpath("./cat/text()").inner_text.downcase,                    :price => "£" + node.xpath("./price/btext()").inner_text) 

would need this, see :category line, (i know following wrong btw!)...

product.create(:name => node.xpath("./text/name/text()").inner_text.downcase,                     :description => node.xpath("./text/desc/text()").inner_text,                    :brand => node.xpath("./brand/text()").inner_text,                    :merchant => node.xpath("../@name").inner_text,                    :category => << category.find_by_name(node.xpath("./cat/text()").inner_text.downcase),                    :price => "£" + node.xpath("./price/btext()").inner_text) 

any ideas? make sense!?

assuming columns called category_name , merchant_name, , you've set associations on category , merchant, this:

product.all |product|   product.category = category.find_or_create_by_category_name(product.category_name)   product.merchant = merchant.find_or_create_by_merchant_name(product.merchant_name)   product.save! end 

it take while, large datasets might need better solution.

so set :category value in products table category_id or set value category_name?

.find_or_create_by find on attribute , returns matching row, or creates 1 if not exist. when creating association via `.category=, rails set foreign key match id of row in categories table.

so answer question more directly:

product.create(:category=>category.find_or_create_by_name("magic beans")) 

is doing this:

category = category.find_by_name("magic beans") if category.nil?   category = category.create(:name=>"magic beans") end product = product.new product.category = category product.save 

where penultimate step sets foreign key category_id value category.id. convention associations set such foreign key model name suffixed _id, products table should have both category_id , merchant_id.