MongoDB : Can't insert twice the same document

Question

On my pymongo code, inserting twice the same doc raises an error :

document = {"auteur" : "romain",
            "text" : "premier post",
            "tag" : "test2",
            "date" : datetime.datetime.utcnow()}
collection.insert_one(document)
collection.insert_one(document)

raises :

DuplicateKeyError: E11000 duplicate key error collection: test.myCollection index: _id_ dup key: { : ObjectId('5aa282eff1dba231beada9e3') }

inserting two documents with different content works fine.

Seems like according to https://docs.mongodb.com/manual/reference/method/db.collection.createIndex/#options I should do something aobut option of indexes:

unique  boolean 
Optional. Creates a unique index so that the collection will not accept insertion or update of documents where the index key value matches an existing value in the index.

Specify true to create a unique index. The default value is false.

The option is unavailable for hashed indexes.

I am looking at : https://docs.mongodb.com/manual/reference/method/db.collection.createIndex/#options — Romain Jouin, Mar 09 '18 at 13:05
That's the issue you can see the error message `duplicate key error collection` — Rahul Sharma, Mar 09 '18 at 13:06
How can I create a collection without a unique validation in the schema ? — Romain Jouin, Mar 09 '18 at 13:07
There is a unique index existing in the collection. What do you have from running `print(collection.list_indexes())` — Oluwafemi Sule, Mar 09 '18 at 13:30

score 2 · Answer 1 · answered Mar 10 '18 at 15:37

Adding to Peba's answer, you can use the .copy() method of python dictionary to avoid the mutation of the document itself.

document = {"auteur" : "romain",
            "text" : "premier post",
            "tag" : "test2",
            "date" : datetime.datetime.utcnow()}
collection.insert_one(document.copy())
collection.insert_one(document.copy())

This way, each insert_one call get's a shallow copy of the document and at the same time keeps your code more pythonic.

score 0 · Answer 2 · answered Mar 09 '18 at 13:42

Inserting a document implicitly generates an _id. So after inserting the document it will mutate to

document = {"_id" : ObjectId('random_id_here'),
            "auteur" : "romain",
            "text" : "premier post",
            "tag" : "test2",
            "date" : datetime.datetime.utcnow()}

Trying to insert said document again will result in an error due to the duplicated _id.

You can create a new document with the same values and insert it.

document = {"auteur" : "romain",
            "text" : "premier post",
            "tag" : "test2",
            "date" : datetime.datetime.utcnow()}
collection.insert_one(document)

document = {"auteur" : "romain",
            "text" : "premier post",
            "tag" : "test2",
            "date" : datetime.datetime.utcnow()}
collection.insert_one(document)

that's strange. And the error disapear with the "save" method, which I use now (but is deprecated) — Romain Jouin, Mar 09 '18 at 13:54
@romainjouin The save method is doing an upsert if an `_id`is already present in the document, so it's replacing the existing document instead of creating a new one. You can find more at [the docs](https://docs.mongodb.com/manual/reference/method/db.collection.save). I advise to not use it tho, and go for the non deprecated alternatives `insert_one()` or `replace_one()` instead. — Peba, Mar 09 '18 at 14:08

MongoDB : Can't insert twice the same document

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