Most efficient way to store nested categories (or hierarchical data) in Mongo?

Question

We have nested categories for several products (e.g., Sports -> Basketball -> Men\'s, Sports -> Tennis -> Women\'s ) and are using Mongo instea

Answer 1

If all categories are distinct then think of them as tags. The hierarchy isn't necessary to encode in the items because you don't need them when you query for items. The hierarchy is a presentational thing. Tag each item with all the categories in it's path, so "Sport > Baseball > Shoes" could be saved as {..., categories: ["sport", "baseball", "shoes"], ...}. If you want all items in the "Sport" category, search for {categories: "sport"}, if you want just the shoes, search for {tags: "shoes"}.

This doesn't capture the hierarchy, but if you think about it that doesn't matter. If the categories are distinct, the hierarchy doesn't help you when you query for items. There will be no other "baseball", so when you search for that you will only get things below the "baseball" level in the hierarchy.

My suggestion relies on categories being distinct, and I guess they aren't in your current model. However, there's no reason why you can't make them distinct. You've probably chosen to use the strings you display on the page as category names in the database. If you instead use symbolic names like "sport" or "womens_shoes" and use a lookup table to find the string to display on the page (this will also save you hours of work if the name of a category ever changes -- and it will make translating the site easier, if you would ever need to do that) you can easily make sure that they are distinct because they don't have anything to do with what is displayed on the page. So if you have two "Shoes" in the hierarchy (for example "Tennis > Women's > Shoes" and "Tennis > Men's > Shoes") you can just add a qualifier to make them distinct (for example "womens_shoes" and "mens_shoes", or "tennis_womens_shoes") The symbolic names are arbitrary and can be anything, you could even use numbers and just use the next number in the sequence every time you add a category.