Getting "err" : "E11000 duplicate key error when inserting into mongo using the Java driver

Question

Exception in thread "main" com.mongodb.MongoException$DuplicateKey: { "serverUsed" : "localhost/127.0.0.1:27017" , "err" : "E11000 duplicate key error index: twitterdb03.LevelAFollowers.$id dup key: { : ObjectId('52d5636de408652b4853a8fe') }" , "code" : 11000 , "n" : 0 , "connectionId" : 12 , "ok" : 1.0}

I'm using mongo 2.11.1

Never had problems with simple write operations in java

myMap.put(inid, followersList);
myObj.putAll(myMap);
myIdMapCollection.insert(myObj);

Answer 1

I found an answer on this page. I’m guessing your code looks something like this (greatly simplified)?:

doc = {} 
for i in xrange(2): 
    doc['i'] = i 
    collection.insert(doc) 

The problem is that PyMongo injects an _id field into the document, if the _id field does not exist, before inserting it (_id is always generated client side with 10gen drivers). That means that the first time through the loop _id is added by the insert method. Since doc is defined outside the loop, each subsequent pass through the loop uses the same value for _id.

Solution:

1. Delete the key _id

for i in xrange(2): 
    doc['i'] = i 
    if '_id' in doc: 
        del doc['_id'] 
    collection.insert(doc)

2. Or create manually a new one:

from bson.objectid import ObjectId 
for i in xrange(2): 
    doc['i'] = i 
    doc['_id'] = ObjectId() 
    collection.insert(doc)