Ruby on Rails

I've got two tables in my Postgres database: categories and products.

I have a one to many relationship defined, one category can have many products.

I then created a reference and migrated the tables.

AddCategoryRefToProducts category:references

I have this in my models.

#product.rb  belongs_to :category    #category.rb  has_many :products

I've fixed the _form to include the category id.   But when I edit or update the form, the category id is not written to the product table.

I think I'm missing a step somewhere, not sure where.

Any suggestions?

Thanks,

Joe