NickName:deadbits Ask DateTime:2015-10-18T01:06:10

Append item to MongoDB document array in PyMongo without re-insertion

I am using MongoDB as the back-end database for Python web application (PyMongo + Bottle). Users can upload files and optionally 'tag' these files during upload. The tags are stored as a list within the document, per below:

{
    "_id" : ObjectId("561c199e038e42b10956e3fc"),
    "tags" : [ "tag1", "tag2", "tag3" ],
    "ref" : "4780"
}

I am trying to allow users to append new tags to any document. I came up with something like this:

def update_tags(ref, new_tag)
    # fetch desired document by ref key as dict
    document = dict(coll.find_one({'ref': ref}))
    # append new tag
    document['tags'].append(new_tag)
    # re-insert the document back into mongo
    coll.update(document)

(fyi; ref key is always unique. this could easily be _id as well.) It seems like there should be a way to just update the 'tags' value directly without pulling back the entire document and re-inserting. Am I missing something here?

Any thoughts are greatly appreciated :)

Copyright Notice：Content Author:「deadbits」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/33189258/append-item-to-mongodb-document-array-in-pymongo-without-re-insertion

Answers

styvane 2015-10-17T17:18:37

You don't need to use to retrieve the document first just use the .update method with the $push operator.\n\ndef update_tags(ref, new_tag):\n coll.update({'ref': ref}, {'$push': {'tags': new_tag}})\n\n\nSince update is deprecated you should use the find_one_and_update or the update_one method if you are using pymongo 2.9 or newer",

Kiluvya.A 2017-09-15T02:05:23

Just to add to @ssytvane answer,and to answer @Guarav: you can add \"upsert = True\" if it does not exist:\n\ndef update_tags(ref, new_tag):\n coll.update({'ref': ref}, {'$push': {'tags': new_tag}}, upsert = True)\n\n\nor\n\ndef update_tags(ref, new_tag):\n coll.update_one({'ref': ref}, {'$push': {'tags': new_tag}}, upsert = True)\n",

Nikhil Fulzele 2017-10-12T05:47:52

You can simply do\n\n1) If you want to append single entry\n\ndef update_tags(ref, new_tag):\n coll.update({'ref': ref}, {'$push': {'tags': new_tag}})\n\n\neg: \n\n{\n \"_id\" : ObjectId(\"561c199e038e42b10956e3fc\"),\n \"tags\" : [ \"tag1\", \"tag2\", \"tag3\" ],\n \"ref\" : \"4780\"\n}\n>> update_tags(\"4780\", \"tag4\")\n{'updatedExisting': True, u'nModified': 1, u'ok': 1, u'n': 1}\n>> coll.find_one({\"ref\":\"4780\"})\n{\n \"_id\" : ObjectId(\"561c199e038e42b10956e3fc\"),\n \"tags\" : [ \"tag1\", \"tag2\", \"tag3\" , \"tag4\" ],\n \"ref\" : \"4780\"\n}\n\n\n2) If you want to append multiple entries\n\ndef update_tags(ref, new_tag):\n coll.update({'ref': ref}, {'$pushAll': {'tags': new_tag}}) #type of new_tag is list\n\n\neg: \n\n{\n \"_id\" : ObjectId(\"561c199e038e42b10956e3fc\"),\n \"tags\" : [ \"tag1\", \"tag2\", \"tag3\" ],\n \"ref\" : \"4780\"\n}\n>> update_tags(\"4780\", [\"tag5\", \"tag6\", \"tag7\"])\n{'updatedExisting': True, u'nModified': 1, u'ok': 1, u'n': 1}\n>> coll.find_one({\"ref\":\"4780\"})\n{\n \"_id\" : ObjectId(\"561c199e038e42b10956e3fc\"),\n \"tags\" : [ \"tag1\", \"tag2\", \"tag3\" , \"tag4\" , \"tag5\", \"tag6\", \"tag7\" ],\n \"ref\" : \"4780\"\n}\n\n\nNote: If the key is not already present, then mongo will create new key.",

ArminMz 2020-03-30T14:03:14

There had been some good answers that are correct but in my opinion writing update_tags this way is better and more usable:\n\ndef update_tags(ref, *args):\n coll.update_one(ref, {'$push': {'tags': {'$each': args}}})\n\n\nthis way you can do both appending one tag or appending many tags:\n\n>> update_tags(ref, 'tag5')\n\n\n>> update_tags(ref, 'tag5', 'tag6')\n\n\n>> list_of_new_tags = do_something_that_returns_list_of_tags()\n>> update_tags(ref, *list_of_new_tags)\n",