Is there a way to add an incrementing id in one statement in MongoDB?

user_12513887 0
Viewed 517

So I got a small database, It's not going to grow much more and I'm trying to get one document from the db in an API that I implemented in python so that with a given document Id I retrieve the document in the db. However, I find it a little hard to put the user to write a random number from the db. All I require is a function that modifies each document by setting an id field and to Auto-Increment. As I said, it's not going to grow that much and the performance isn't really an issue here.

So far what I've been able to do is this:

var i = 0
db.MyCollection.update({},
                          {$set : {"new_field":1}},
                          {upsert:false,
                          multi:true}
i ++;),

I achieved to set an id field but it sets the same number to each document (the count of every document) So let's say that if the db has 10 docs, it'll set the Id to 10.

mongo-shell pymongo mongodb python-3.x
2 Answers

Find-and-modify operation returns the document updated (before or after the update depending on returnDocument setting). You can use this with $inc to implement a counter. Ruby example where c is a collection:

irb(main):005:0> c['foo'].insert_one(counter:true,count:1)
=> #<Mongo::Operation::Insert::Result:0x8040 documents=[{"n"=>1, "opTime"=>{"ts"=>#<BSON::Timestamp:0x00005609f260b7e0 @seconds=1594961771, @increment=2>, "t"=>1}, "electionId"=>BSON::ObjectId('7fffffff0000000000000001'), "ok"=>1.0, "$clusterTime"=>{"clusterTime"=>#<BSON::Timestamp:0x00005609f260b538 @seconds=1594961771, @increment=2>, "signature"=>{"hash"=><BSON::Binary:0x8060 type=generic data=0x0000000000000000...>, "keyId"=>0}}, "operationTime"=>#<BSON::Timestamp:0x00005609f260b290 @seconds=1594961771, @increment=2>}]>

irb(main):011:0> c['foo'].find_one_and_update({counter:true},{'$inc':{count:1}})
=> {"_id"=>BSON::ObjectId('5f112f6b2c97a6281f63f575'), "counter"=>true, "count"=>1}
irb(main):012:0> c['foo'].find_one_and_update({counter:true},{'$inc':{count:1}})
=> {"_id"=>BSON::ObjectId('5f112f6b2c97a6281f63f575'), "counter"=>true, "count"=>2}
irb(main):013:0> c['foo'].find_one_and_update({counter:true},{'$inc':{count:1}})
=> {"_id"=>BSON::ObjectId('5f112f6b2c97a6281f63f575'), "counter"=>true, "count"=>3}
irb(main):014:0> c['foo'].find_one_and_update({counter:true},{'$inc':{count:1}})
=> {"_id"=>BSON::ObjectId('5f112f6b2c97a6281f63f575'), "counter"=>true, "count"=>4}
user_95409250

Why not just use this logic? Instead of updating all via one query, just launch multiple queries one by one? Mongo will do it pretty fast, even if you have >1M docs in database (according to your phrase: I got a small database) because pre-builded index on _id field.

this is a javasript code, but I guess, you'll understand the logic of it

let all_documents = db.MyCollection.find({});

for (let i = 0; i < all_documents.length; i++) {
  db.MyCollection.update({_id: all_documents[i]._id }, {$set : {"new_field": i}}, {upsert:false})
}
user_74756150
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