Develop Reference

Delete all documents returned in a find().limit()

I'm using db.collection.find({}, {'_id': False}).limit(2000) to get the documents from a collection. This documents are sent to a Facebook API, after the API return success this documents need to be deleted from the collection.
My main doubt is:
Is there a way to I delete all this 2000 documents withou using a for
loop? I know that collection.find returns a cursor, is there a way
to use this cursor in a delete_many?
The structure of my document is:
{
"_id" : ObjectId("61608068887f1a0e2162d94b"),
"event_time" : "1632582893",
"value" : "549.9000",
"contents" : [
{
"product_id" : "1-1",
"quantity" : "1.000000",
"value" : "10"
}
]
}

To solve this problem, based on the comments of #adarsh and #J.F I've used the following code:
rm = [x['_id'] for x in MongoDB(mongo).db.get_collection("DataToSend").find({}, {'_id' : 1}).limit(2000)
MongoDB(mongo).db.get_collection("DataToSend").delete_many({'_id' : { '$in' : list(rm)}})

Extracting and updating a dictionary from array of dictinaries in MongoDB

I have a structure like this:
{
"id" : 1,
"user" : "somebody",
"players" : [
{
"name" : "lala",
"surname" : "baba",
"player_place" : "1",
"start_num" : "123",
"results" : {
"1" : { ... }
"2" : { ... },
...
}
},
...
]
}
I am pretty new to MongoDB and I just cannot figure out how to extract results for a specific user (in this case "somebody", but there are many other users and each has an array of players and each player has many results) for a specific player with start_num.
I am using pymongo and this is the code I came up with:
record = collection.find(
{'user' : name}, {'players' : {'$elemMatch' : {'start_num' : start_num}}, '_id' : False}
)
This extracts players with specific player for a given user. That is good, but now I need to get specific result from results, something like this:
{ 'results' : { '2' : { ... } } }.
I tried:
record = collection.find(
{'user' : name}, {'players' : {'$elemMatch' : {'start_num' : start_num}}, 'results' : result_num, '_id' : False}
)
but that, of course, doesn't work. I could just turn that to list in Python and extract what I need, but I would like to do that with query in Mongo.
Also, what would I need to do to replace specific result in results for specific player for specific user? Let's say I have a new result with key 2 and I want to replace existing result that has key 2. Can I do it with same query as for find() (just replacing method find with method replace or find_and_replace)?

You can replace a specific result and the syntax for that should be something like this,
assuming you want to replace the result with key 1,
collection.updateOne({
"user": name,
"players.start_num": start_num
},
{ $set: { "players.$.results.1" : new_result }})

update nth document in a nested array document in mongo

I need to update a document in an array inside another document in Mongo DB.
{
"_id" : ObjectId("51cff693d342704b5047e6d8"),
"author" : "test",
"body" : "sdfkj dsfhk asdfjad ",
"comments" : [
{
"author" : "test",
"body" : "sdfkjdj\r\nasdjgkfdfj",
"email" : "test#tes.com"
},
{
"author" : "hola",
"body" : "sdfl\r\nhola \r\nwork here"
}
],
"date" : ISODate("2013-06-30T09:12:51.629Z"),
"permalink" : "mxwnnnqafl",
"tags" : [
"ab"
],
"title" : "cd"
}
If I try to update first document in comments array by below command, it works.
db.posts.update({'permalink':"cxzdzjkztkqraoqlgcru"},{'$inc': {"comments.0.num_likes": 1}})
But if I put the same in python code like below, I am getting Write error, that it can't traverse the element. I am not understanding what is missing!!
Can anyone help me out please.
post = self.posts.find_one({'permalink': permalink})
response = self.posts.update({'permalink': permalink},
{'$inc':"comments.comment_ordinal.num_likes": 1}})
WriteError: cannot use the part (comments of comments.comment_ordinal.num_likes) to traverse the element

comment_ordinal should be a substitution, not the index itself. You're treating it like an integer that can be mapped to an ordinal number. I mean you should do something like:
updated_field = "comments." + str(comment_ordinal) + ".num_likes"
response = self.posts.update({'permalink': permalink}, {'$inc': {updated_field: 1}})
Hope this helps.

You are doing it wrong you need to build your query dynamically and the best way to do that is using the str.format method.
response = self.posts.update_one(
{'permalink': permalink},
{'$inc': {"comments.{}.num_likes".format(comment_ordinal): 1}}
)
Also you should consider to use the update_one method for single update and update_many if you need to update multiple documents because update is deprecated.

Pull from a list in a dict using mongoengine

I have this Document in mongo engine:
class Mydoc(db.Document):
x = db.DictField()
item_number = IntField()
And I have this data into the Document
{
"_id" : ObjectId("55e360cce725070909af4953"),
"x" : {
"mongo" : [
{
"list" : "lista"
},
{
"list" : "listb"
}
],
"hello" : "world"
},
"item_number" : 1
}
Ok if I want to push to mongo list using mongoengine, i do this:
Mydoc.objects(item_number=1).update_one(push__x__mongo={"list" : "listc"})
That works pretty well, if a query the database again i get this
{
"_id" : ObjectId("55e360cce725070909af4953"),
"x" : {
"mongo" : [
{
"list" : "lista"
},
{
"list" : "listb"
},
{
"list" : "listc"
}
],
"hello" : "world"
},
"item_number" : 1
}
But When I try to pull from same list using pull in mongo engine:
Mydoc.objects(item_number=1).update_one(pull__x__mongo={'list': 'lista'})
I get this error:
mongoengine.errors.OperationError: Update failed (Cannot apply $pull
to a non-array value)
comparising the sentences:
Mydoc.objects(item_number=1).update_one(push__x__mongo={"list" : "listc"}) # Works
Mydoc.objects(item_number=1).update_one(pull__x__mongo={"list" : "listc"}) # Error
How can I pull from this list?
I appreciate any help

I believe that the problem is that mongoengine doesn't know the structure of your x document. You declared it as DictField, so mongoengine thinks you are pulling from DictField not from ListField. Declare x as ListField and both queries should work just fine.
I suggest you should also create an issue for this:
https://github.com/MongoEngine/mongoengine/issues
As a workaround, you can use a raw query:
Mydoc.objects(item_number=1).update_one(__raw__={'$pull': {'x.mongo': {'list': 'listc'}}})

SyntaxError with pymongo and $ne : null

this is my code :
#! /usr/bin/python
import os
from pymongo.connection import Connection
from pymongo.master_slave_connection import MasterSlaveConnection
database = 'toto'
collection = 'logs'
master = Connection(host="X.X.X.X", port=27017)
slave1 = Connection(host="X.X.X.X", port=27017)
con = MasterSlaveConnection(master, slaves=[slave1, master])
db = getattr(con,database)
#host_name.append("getattr(db,collection).distinct( 'host_name' )")
#print host_name[1]
hosts = db.logs.distinct( 'host_name' )
services = db.logs.distinct("service_description" , { "service_description" : { $ne : null } } )
#print hosts
print services
I got this error :
File "./rapport.py", line 23
services = db.logs.distinct("service_description" , { "service_description" : { $ne : null } } )
^
SyntaxError: invalid syntax
Why i can't use "$ne : null" in my code? I don't understand because when i execute this query "db.logs.distinct("service_description" , { "service_description" : { $ne : null } } )" directly in mongodb it works.
I also tried this but it doesn't work :
services = db.logs.distinct("service_description", { "service_description" : { "$ne" : None } } )
Thanks for your help.

You need to quote the $ne and use None instead of null.
Pymongo uses dicts as parameters.
asdf = "something"
{ asdf: "foo"}
is a valid declaration, using "something" as key.
If you compare that with
{$ne: "foo"}
the interpreter expects a variable name as first entry, and $neis invalid.
Also, nullis not predefined in Python, so use None instead.
Combined with the fluid interface in pymongo, your query should be:
db.logs.find({"service_description": {"$ne" : None}}).distinct('service_description')