ruby on rails - Database design for categorized to-do app -

i'm trying figure out best (most logical) way of designing database app allow user crud to-do tasks (more or less), however, they're organized hard-coded categories.

so let's you're go favorite department store. need hit women's floor , pick girlfriend shoes ordered, , matching dress (which on other side of store, on same floor.) then, need go boy's department little brother, , pick 2 different pairs of shorts, 1 pair of pants, , new pair of shoes.

the women's floor , boy's department 2 examples of categories shopping list items fall into.

so looks this:

* women's floor      1 pair shoes      1 dress  * boy's department      2 shorts      1 pant      1 pair shoes 

so database design so...

categories: id, title listindex: id, user_id shoppinglist: id, listindex_id, category_id, item_id, order, active items: id, name, category_id 

categories boy's department, women's floor, etc. users not able create new categories, instead, predefine categories

listindex provide master relation shopping list whole.

shoppinglist actual shopping list (active 0/1, user have way remind bought item / put in cart.)

items have list of items available put to-do tasks. categorize these ourselves on back-end.

is right way of doing it?

hopefully understood description of problem correctly thinking here's 1 way lay database , models out. don't think need listindex:

database tables

categories: id, title  shoppinglists: id, user_id, order, active  items: id, title  shoppinglistitems: id, item_id, shopping_list_id, quantity  categorizeditems: id, category_id, item_id  users: id, name 

models

user: has_many shopping_lists  shoppinglist: belongs_to user has_many shopping_list_items has_many items, through shopping_list_items  items: has_many categorized_items has_many categories, through categorized_items (optional: query item shopping lists on) has_many shopping_list_items has_many shopping_lists, through shopping_list_items  categories: has_many categorized_items has_many items, through categorized_items 

my thinking --

individual categories static, that's pretty straight forward.
shopping lists represent user's (via user_id) list of items purchased. link between item , shopping list take place in join table called shoppinglistitems each row links relationship between list, item, , quantity.

items interesting because in example item can in multiple categories. i.e. "pants" can in boys/girls/men/women , pets :(. support think can use join table called categorizeditems lets query "items in particular category" or "categories item in".