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)}})

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'}}})

adding a list field in mongo (python)

I have an id which some tags are associated with and I want to fill a collection with those tags. How do I do this?
Suppose I have the following:
key: 12345, tags = ["foo","bar","foobar"]
So I am hoping to get a document in a collection named "Tags" like this:
{
"_id" : ObjectId("4fbaa6076a56b2700d000000"),
"key" : 12345,
"tags" : ["foo","bar","foobar"]
}
How do I do this in python?

mongo_conn.Tags.insert({
"key": 12345,
"tags": ["foo","bar","foobar"]
})

How to Query this in MongoDB?

My items store in MongoDB like this :
{"ProductName":"XXXX",
"Catalogs" : [
{
"50008064" : "Apple"
},
{
"50010566" : "Box"
},
{
"50016422" : "Water"
}
]}
Now I want query all the items belong to Catalog:50008064,how to?
(the catalog id "50008064" , catalog name "Apple")

You cannot query this in an efficient manner and performance will decrease as your data grows. As such I would consider it a schema bug and you should refactor/migrate to the following model which does allow for indexing :
{"ProductName":"XXXX",
"Catalogs" : [
{
id : "50008064",
value : "Apple"
},
{
id : "50010566",
value : "Box"
},
{
id : "50016422",
value : "Water"
}
]}
And then index :
ensureIndex({'Catalogs.id':1})
Again, I strongly suggest you change your schema as this is a potential performance bottleneck you cannot fix any other way.

This should probably work according to the entry here, although this won't be very fast, as stated in in the link.
db.products.find({ "Catalogs.50008064" : { $exists: true } } )