How many BSON ObjectIds can a mongodb array field

问题:

I am planning to save huge number of ids for foreignkey ids in this array. So, I am just checking what would be the max number of BSON::ObjectIds I can save in the field array. Lets say for example

department_ids: [BSON::OBjectId('57cf6d6e8315292136000001'), BSON::OBjectId('57cf6d6e8315292136000002') ...... ]

回答1:

16MB is big enough to hold really large amount of ObjectId, ObjectIds aren't that heavy, they are 12 bytes and when you divide it by 16MB you get well beyond 1 million.

But in case you still aren't assured, you can benefit by the flexible schema design of Mongo and create one follow-up document to hold further arrays and store the _id of that document in the concerned document with a field named as "followedBy" or something.

downside is you will have to execute a follow-up query (or maybe not).

Hope that helps.

回答2:

No such limit mentioned in documents of monogdb for it but a javascript array can have upto 2^32-1 = 4,294,967,295 = 4.29 billion elements.

And mongodb document could have upto 16MB.

回答3:

There is no limit on the number of objects you put in an array. However, the document that contain that array can not exceed 16 megabytes.

MongoDB Limits and Thresholds

回答4:

Every ObjectID uses 12 bytes, if the limit is 16 MB you could have approximately 1398101 objectsID in a array per document.

Maybe the DBRefs could help you, or you could use a GridFS collection.

If you could avoid the joins that would be the best solution on mongo.