is mongoose generated sub-document _id unique

Question

Using the following mongoose schema

mongoose.Schema({
    world: String,
    color: [{ name: String }]
});

Gives me document that have sub-documents containing _id fields.

{ _id: 'a9ec8475bf0d285e10ca8d42'
  world: 'matrix', 
  color: [
    { name: 'blue',  _id: '4a8c0e12135fa32e13db9ce9' },
    { name: 'red',   _id: '4a8c0a62254cd32e13db4ad8' },
    { name: 'white', _id: '4a8c04e2687ea32e13db1da7' }
]

I want to know if each of these sub-documents _id are unique across all documents, or only across the nested level it is in.

Edit: the sub-document doesn't refer to another collection, it's created with the plain mongoose schema above.

https://docs.mongodb.com/manual/core/document/#the-id-field – Serge K. Jan 16 '18 at 15:31 — Serge K., Jan 16 '18 at 15:31
@SergeK. This doesn't mention _ids of sub-documents. – Saitama Jan 16 '18 at 15:33 — Saitama, Jan 16 '18 at 15:33

score 0 · Answer 1 · answered Jan 16 '18 at 15:19

0

I assume the sub-document references another collection. If my assumption is right then the nested documents you have are only unique only on the nested level.

answered Jan 16 '18 at 15:19

Ossaija Thankgod

454
5
9

It doesn't refer to another collection. It's created with simple mongoose schema in the question. – Saitama Jan 16 '18 at 15:23
Can you show the code you use to insert into the collection? – Ossaija Thankgod Jan 16 '18 at 15:31
It's a mongoose operation: ```new model({ world: 'matrix', color: [{name: 'red'}, {name: 'blue'}, {name: 'white'}] })``` – Saitama Jan 16 '18 at 15:35

score 0 · Answer 2 · answered Jan 16 '18 at 15:52

0

This is an issue with Mongoose. Mongoose creates schemas for each of those nested objects behind the scenes. That means the _id is only unquie on the nested level.

Look at this previous question on how to prevent this from happening

answered Jan 16 '18 at 15:52

Ossaija Thankgod

454
5
9

is there a way to make this _id unique across entire collection? – Saitama Jan 17 '18 at 05:01
You can assign the _id value by yourself. there are UUID packages on npm to achieve that. – Ossaija Thankgod Jan 17 '18 at 10:06

is mongoose generated sub-document _id unique

2 Answers2