MongoDB insert raises duplicate key error

You need to understand that your entries list has a bunch of references to one entry dict. So when PyMongo sets entries[0]['_id'], all the other entries get the same _id. (In fact, PyMongo will iterate through the list setting each entry's _id, so all the entries will have the final _id at the end.) A quick fix would be:

entries.append(entry.copy())

This is merely a shallow copy, but in the code you shared I believe this is enough to fix your problem.

I had the same error using insert_one() and also insert_many()

My solution is, to use update_one() with upsert=True

  doc = {a: 1, b:2, x:{xx:"hello",yy:"world"}}
  db.collection.update_one(doc,{'$set':doc},upsert=True)

This works for me :-)

Make sure variable 'entries' is cleared after every insert.

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). That means that the first time through the loop _id is added by the insert method. Since 'entries' is defined outside, each subsequent pass through the loop uses the same value for _id.

Clear the dict variable in top of the loop statements.

OR

Remove _id from the dict. Eg:

del my_dict['_id'] 

Delete the key "_id":

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

Or manually create a new one:

from bson.objectid import ObjectId

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

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