CODEWITHSUNDEEP
mongodbforeign-keysobjectid
Francisco Costa
Francisco Costa

Reputation: 7113

MongoDB storing arrays of ObjectId's

In my database I have to store an array of object ids. What should I use? Something like this:

[ObjectId("50350e12a36feb1be6000364"), ObjectId("57350e12a37fef1be6000922"), ObjectId("10350e17d34ffb1be6200925")]

or something like this: 

["50350e12a36feb1be6000364", "57350e12a37fef1be6000922", "10350e17d34ffb1be6200925"]

I could save space with the second, and then cast to ObjectId, but am I loosing anything by using this approach? Do ObjectIds behave like foreign keys in relational databases?

Upvotes: 18

Views: 3372

Answers (2)

jhonkola
jhonkola

Reputation: 3435

I would definitely go with the first approach, storing the ObjectIds directly. This saves space, as ObjectId is 12 bytes whereas the second approach string is 24 bytes.

Also, if the ObjectIds are used to fetch the objects later, storing as ObjectId saves some hassle.

Upvotes: 26

JohnnyHK
JohnnyHK

Reputation: 311855

Unless you have a good reason not to, store them as an array of ObjectIds. It's more compact (12 bytes vs. 24) and it more accurately reflects what's stored. It can also enable driver-level support for following ObjectId references.

Upvotes: 11

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