Say i have this database "list", which contains a collection called "users", which contain, among others, an object called "david"
{u'_id': u'david', u'url': u'url3', u'old_url': u'url3', u'wishlist': [[u'Jenara', u'shards', u'nm'], [u'force of will', u'mm2', u'nm'], [u'pact of negation', u'mm', u'nm'], [u'all is dust', u'mm4', u'nm']]}
how can i use pymongo to edit the arrays within the wishlist field? say i want to remove one of the four arrays, or edit one of them?
In order to update an element in an array, use $set. Here is an example - updating the second element and setting it's value to ["something", "else"]:
db.users.update({'_id': 'david'}, {"$set": {"wishlist.1": ["something", "else"]}})
As for the removing an item from an array by index, it's not that easy and straightforward, see:
In mongoDb, how do you remove an array element by its index
How to delete n-th element of array in mongodb
Related
Say I have a document that contains an array named Months. Each element in the array has a int field indicating which month & year it refers to (yyyyMM), e.g. 201612, 201701, etc.
Each such element also contains additional fields, pertaining to that particular month. e.g. int numOfItems, string Country, etc.
Now, assuming I have such document with only 2 elements in the array:
Months[0].month == 201612
Months[1].month == 201701
Then, I call addToSet with Months[1].month == 201701.
How does addToSet determine whether this is a duplicate or not?
Does it inspect and compare all sub-elements of Months[1] to do that? Does it only inspect the index of the element in the Months array?
This is directly from MongoDB.
MongoDB - AddToSet
If the value is a document, MongoDB determines that the document is a duplicate if an existing document in the array matches the to-be-added document exactly; i.e. the existing document has the exact same fields and values and the fields are in the same order. As such, field order matters and you cannot specify that MongoDB compare only a subset of the fields in the document to determine whether the document is a duplicate of an existing array element.
Apologies if this is a re-post, but I wasn't able to quite get the query I want from the mongodb documentation examples.
Here's my issue. I am unable execute in a single query to either update an array_field of an existing document or add a new document and initialize the array_field with an initial value.
I can use findOne() with some conditional logic, and probably solve this, but I would think mongodb has an implementation of this use case
Here's the code so far:
#data_json = JSON document to be added to collection
collection.update_one({"json_id":data_json["json_id"], "_dashbd_id_":dashboard_id},{{"$addToSet": {"array_field":keyword}},{"$setOnInsert":data_json}}, upsert=True)
I'm querying by the json_id, and _dashbd_id_ from my collection. If it exists, then I intend to add the "keyword" to the array_field. If it doesn't exist, create a new document as data_json which include array_field = [keyword]
Any hints and suggestions are appreciated!
If I understood you correctly you want to update values in Database only if they do not exist as well as create new documents with arrays in them. Okay there is a way in mongodb which I will mention in this reply. I think you should know few commands first that will help you achieve similar result (again there is a simple way just read on)
Let me start with the first part:
to update an element in an array you use dot notation to the index example:
db.collection_name.update({"_id": id}, {'$set': {"array_name.indexNumber": value}})
say we have the following document in collection name cars
db.cars.findOne():
{
_id: 1
name: EvolutionX
brand: Mitsubish
year: 2012
mods: [ turbo, headlights ]
}
Say in the above example we want to update headlights with rearlights we do the following (using mongoshell you can drop quotes in key names, Not when using the array index though):
db.cars.update({id:1}, {$set:{"mods.1":"rearlights"}})
1 is the index to headlights.
Note and be careful here that if you did not use index inside of an array like
db.cars.update({id:1}, {$set:{"mods":"rearlights"}})
this will overwrite the existing document _id:1 and it will lose all other attributes or fields inside the document so it will result in the follow:
db.cars.findOne():
{
_id: 1
mods: [ rearlights ]
}
Now, say we want to add an element tires to mods array you can use $push as:
db.collection_name.update({"_id": id}, {'$push': {"array_name": value}})
so it will be
db.cars.update({"_id":1}, {"$push":{"mods":"tires"}})
now say instead of updating mods array you want to remove "headlights". In this case you use $pop
db.cars.update({"_id":1}, {"$pop":{"mods":"headlights"}})
Now with that in mind. The easy way: in mongodb to add to array only if element does not exist you can use $addToSet. I love this operator because it will only add to array if the element does not exist. Here is how to use it:
db.cars.update({"_id":1}, {"$addToSet":{"mods":"headlights"}})
Now if headlights is in the array it will not be added, else it will be added to the end of array.
Okay that is the first part of the question. The second part which is initializing a document with an array. Okay there are two thoughts here: the first is you do not have to. using the addToSet you can create the array if it does not exist as (assuming _id 2 exist but without mods array):
db.cars.update({"_id":2}, {"$addToSet":{"mods":"bonnet"}})
This will create the array if document _id:2 exist. Assuming _id:3 does not exist you will have plug in a third attribute called upsert
db.cars.update({"_id":3}, {"$addToSet":{"mods":"headlights"}}, {upsert:true})
this will create a third document with array mods with headlights inside of it and _id:3. Note though no other attributes will be added only the _id and mods array
the second thought is when you insert a new document you insert it with empty mods array as mod:[]
I hope that helps
suppose your data_json ,dashboard_id and keyword contain following detail.
dashboard_id = ObjectId("5423200e6694ce357ad2a1ac")
keyword = "testingKeyword"
data_json =
{
"json_id":ObjectId("5423200e6694ce357ad2a1ac"),
"item":"EFG222",
"reorder":false,
}
if you execute below query
db.collection_name.update({"json_id":data_json["json_id"], "_dashbd_id_":dashboard_id},{{"$addToSet": {"array_field":keyword}},{ upsert=True})
than it will push keyword to array_field if document exist or it will insert new document with following detail as below.
{
"_id":ObjectId("5sdvsdv6sdv694ce357ad2a1ac"),
"json_id":ObjectId("5423200e6694ce357ad2a1ac"),
"dashboard_id": ObjectId("sddfb6694ce357ad2a1ac")
"item":"EFG222",
"reorder":false,
"array_field":
[
"testingKeyword"
]
}
I am using mongodb update method with upsert=true.
My data looks like this:
{"my_id":"1",
"test_list":[{"test_id":1,"test_name":"pppp"}]}
now I am using the following command:
db.testcol.update({"my_id":1,"test_list.test_id":2},{"$set":{"test_list.$.test_name":"mmmm"}},true,true)
Now I want a new object inserted into the "test_list" as it does not exist
but I am getting the error:
Cannot apply the positional operator without a corresponding query field containing an array.
I cannot use "insert" for my operation, as I dont know whether the data is their and the field needs to be updated,or its not their and needs to be inserted(for the first time)
Upserts are for when you want the update to work whether the entire document is there or not, not just an array element. For the array element case you can use $addToSet:
db.testcol.update(
{"my_id": "1"},
{"$addToSet": {"test_list": {"test_id": 2, "test_name": "mmmm"}}})
It will only add the new element to the doc's test_list array field if a matching element isn't already present.
What I'm trying to do:
Filter a field of a collection that matches a given condition. Instead of returning every item in the field (which is an array of items), I only want to see matched items.
Similar to
select items from test where items.histPrices=[10,12]
It is also similar to what's found on the mongodb website here: http://www.mongodb.org/display/DOCS/Retrieving+a+Subset+of+Fields
Here's what I have been trying:
db.test.save({"name":"record", "items":[{"histPrices":[10,12],"name":"stuff"}]})
db.test.save({"name":"record", "items":[{"histPrices":[10,12],"name":"stuff"},
{"histPrices":[12,13],"name":"stuff"},{"histPrices":[11,14],"name":"stuff"}]})
db.test.find({},{"name":1,"items.histPrices":[10, 12]})
It will return all the objects that have a match for items.histPrices:[10,12], including ALL of the items in items[]. But I don't want the ones that don't match the condition.
From the comments left on Mongodb two years ago, the solution to get only the items with that histPrices[10,12] is to do it with javascript code, namely, loop through the result set and filter out the other items.
I wonder if there's a way to do that with just the query.
Your find query is wrong
db.test.find({},{"name":1,"items.histPrices":[10, 12]})
Your condition statement should be in the first part of the find statement.In your query {} means fetch all documents similar to this sql
select items from test (no where clause)
you have to change your mongodb find to
db.test.find({"items.histPrices":[10, 12]},{"name":1})
make it work
since your items is an array and if you wanted to return only the matching sub item, you have to use positional operator
db.test.find({"items.histPrices":[10, 12]},{"name":1,'items.$':1})
When working with arrays Embedded to the Document, the best approach is the one suggested by Chien-Wei Huang.
I would just add another aggregation, with the $group (in cases the document is very long, you may not want to retrieve all its content, only the array elements) Operator.
Now the command would look like:
db.test.aggregate({$match:{name:"record"}},
{$unwind:"$items"},
{$match {"items.histPrices":[10, 12]}},
{$group: {_id: "$_id",items: {$push: "$items"}}});)
If you are interested to return only one element from the array in each collection, then you should use projection instead
The same kind of issue solved here:
MongoDB Retrieve a subset of an array in a collection by specifying two fields which should match
db.test.aggregate({$unwind:"$items"}, {$match:{"items.histPrices":[10, 12]}})
But I don't know whether the performance would be OK. You have to verify it with your data.
The usage of $unwind
If you want add some filter condition like name="record", just add another $march at first, ex:
db.test.aggregate({$match:{name:"record"}}, {$unwind:"$items"}, {$match:{"items.histPrices":[10, 12]}})
https://jira.mongodb.org/browse/SERVER-828
Get particular element from mongoDB array
MongoDB query to retrieve one array value by a value in the array
I am using MongoDB with node.js. Is it possible to persist data as an (unordered) set in MongoDB directly? Or do I have to either
persist them as an array and transform it into a set in JavaScript
or
persist them as an object in the form of {entry1: true, entry2: true, ...}
If I have to do it in either of the two ways above, which one is more efficient? Considering I need to add/remove items frequently, but rarely need to re-assign the whole set/array.
You can manipulate an array as a set in MongoDB... relevant operators include:
$addToSet - The $addToSet operator adds a value to an array only if the value is not in the array already.
$push - The $push operator appends a specified value to an array.
$pop - The $pop operator removes the first or last element of an array.
$pull - The $pull operator removes all instances of a value from an existing array.
$elemMatch - The $elemMatch operator matches more than one component within an array element.