Is it possible to make a "not modify " constrain on MongoDb subdocuments at creation?

Question

I'd like to make a specific subdocument value from a MondoDb document fixed, so it can not be possible to modify it at a next update, or any other MongoDb operations that can modify documents.
For example, if a document like the one bellow is inserted, I will like that "eyesColor" value can not be changed.
{
"id" : "someId",
"name": "Jane",
"eyesColor" : "blue"
}

A possible update can be:
{
"id" : "someId",
"name": "Amy",
"eyesColor" : "green"
}
And the result I need after this update is :
{
"id" : "someId",
"name": "Amy",
"eyesColor" : "blue"
}
I'd like to do this because the possibility of using $set and $unset operators is not present in the project I'm creating. A read on the existing document before the update, in order to get the value of the subdocument ("eyesColor") will decrease the performance of the application I work on.

Actually the constrain I need is similar to the fixed size on collections (capped collections). The difference is that it is on a subdocument instead of collection and on the value contained in the subdocument instead of the size.

Is there any solution to this type of constrain?

Is this schoolwork? What `update`s have you tried? You can specify conditions. — WiredPrairie, Nov 21 '13 at 11:57
@WiredPrairie No, is an extracurricular project. I've used DbCollection.update(DBObject q , DBObject o , boolean upsert , boolean multi) with upsert and multi on 'false'. Thanks — Roxana, Nov 21 '13 at 12:14
If you're trying to selectively insert only some fields, you can't. You need to either do it as two queries, or build it into your business logic. — WiredPrairie, Nov 21 '13 at 13:05
well then, I'll go with two queries, since the resources I'm working on are not that big. Thanks — Roxana, Nov 21 '13 at 14:44
"the possibility of using $set and $unset operators is not present in the project" <- **Why??** — Philipp, Nov 21 '13 at 15:01

Philipp · Answer 1 · 2013-11-21T15:02:23.437

0

There are no constraints in MongoDB (only exception: unique indexes). There is no way to make fields "read-only" on the database-layer.

When you want to use upsert's (db.collection.update with upsert: true) which add certain fields on inserting new documents but don't affect these fields on updates of existing documents, you can place these fields behind the $setOnInsert-operator.

edited Nov 21 '13 at 15:02

answered Nov 21 '13 at 14:56

Philipp

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Is it possible to make a "not modify " constrain on MongoDb subdocuments at creation?

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