When to use an array of objects or an object of objects in MongoDB Design?

Question

I have a question about the general guidance of how to properly mongodb design:

Scenario: I have many collection of objects, all uniquely identified by their contract_address, and i want to be able to pull from there when need be. I found this post, but it didn't seem like enough reasoning.

so would it make sense to have each document have structure A or structure A

structure A - objects of objects

{
"name": "Peter".
"all_nfts": {
   "0x202": {...},
   "0x342": {...},
   ...
}

or structure B - array of objects

{
"name": "Peter".
"all_nfts": [
   {"contract_address" : "0x202", ...},
   {"contract_address" : "0x340", ...},
   ...
]

I would think that structure A would make the most sense because you can just index into the all_nfts field to find the the object corresponding to it, instead of searching through an array which could be O(n) time instead O(1). I was told structure B was better by other experienced MongoDB devs but I don't understand why.

I was told structure B was better by other experienced MongoDB devs but I don't understand why . How do you map option A on the client side? — Laiv
– Laiv, Commented Dec 2, 2022 at 12:32
Sure. If you had to load and map Op A data structure to a model (data structure) of your programing language. How would that model be? If your programing language is statically typed, you might find OP A to be a problem. Maybe, those who said OP is B is better, what they was saying is that B is the less problematic when it comes to be loaded and mapped to data structures of their programming languages — Laiv
– Laiv, Commented Dec 3, 2022 at 11:14

user397399 · Accepted Answer · 2022-12-03 10:49:04Z

It is generally recommended to use an array of objects when designing a MongoDB database. An array of objects allows you to store multiple items in a single field, and it allows you to easily add, remove, and modify individual items within the array.

For example, if you have a collection of users and each user has a list of friends, you could use an array of objects to store the list of friends for each user. This would allow you to easily add, remove, and modify the friends for each user, and it would also allow you to easily query and filter the data based on the friends of each user.

On the other hand, an object of objects is generally not recommended for use in MongoDB design. An object of objects is a more complex data structure that is difficult to work with and to query. It is not as flexible as an array of objects, and it is not as efficient for storing and querying large amounts of data.

Overall, it is generally recommended to use an array of objects when designing a MongoDB database. An array of objects is a simple and flexible data structure that allows you to store and query data efficiently and effectively. An object of objects is not recommended for use in MongoDB design, as it is a more complex and less efficient data structure.

Flater · Accepted Answer · 2022-11-01 23:24:07Z

1

Use B when you have a collection of items that you intend to iterate over.

Use A when you have a collection of items that you with to store in a key/value pair for directly looking up an item based on its key. This is assuming you work in a language that allows dynamic data structures, e.g. TypeScript. While JSON inherently allows for it, the language you're working in might not.

answered Nov 1, 2022 at 23:24

Flater

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