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Find and update value in array of nested objects in mongo [duplicate]

I have this collection:
[{ "_id" : 7,
"category" : "Festival",
"comments" : [
{
"_id" : ObjectId("4da4e7d1590295d4eb81c0c7"),
"usr" : "Mila",
"txt" : "This is a comment",
"date" : "4/12/11"
}
]
}]
All I want is to push insert a new field inside comments like this:
[{ "_id" : 7,
"category" : "Festival",
"comments" : [
{
"_id" : ObjectId("4da4e7d1590295d4eb81c0c7"),
"usr" : "Mila",
"txt" : "This is a comment",
"date" : "4/12/11",
"type": "abc" // find the parent doc with id=7 & insert this inside comments
}
]
}]
How can I insert inside the comments subdocument?

You need to use the $ positional operator
For example:
update({
_id: 7,
"comments._id": ObjectId("4da4e7d1590295d4eb81c0c7")
},{
$set: {"comments.$.type": abc}
}, false, true
);
I didn't test it but i hope that it will be helpful for you.
If you want to change the structure of document you need to use
db.collection.update( criteria,
objNew, upsert, multi )
Arguments:
criteria - query which selects the record to update;
objNew - updated object or $ operators (e.g., $inc) which manipulate the object
upsert - if this should be an "upsert"; that is, if the record does not exist, nsert it
multi - if all documents matching criteria should be updated
and insert new objNew with new structure. check this for more details

The $ positional operator is only going to work as expected if the 'comments' field is NOT an array. The OP's json is malformed, but it looks like it could be an array.
The issue is that mongodb right now will only update the first element of an array which matches the query. Though there is an RFE open to add support for updating all matching array elements: https://jira.mongodb.org/browse/SERVER-1243
To work around this issue with arrays you just have to do a regular find then update the elements in the array individually.

Mongoose search for items on array containing _id with aggregate [duplicate]

If I have this schema...
person = {
name : String,
favoriteFoods : Array
}
... where the favoriteFoods array is populated with strings. How can I find all persons that have "sushi" as their favorite food using mongoose?
I was hoping for something along the lines of:
PersonModel.find({ favoriteFoods : { $contains : "sushi" }, function(...) {...});
(I know that there is no $contains in mongodb, just explaining what I was expecting to find before knowing the solution)

As favouriteFoods is a simple array of strings, you can just query that field directly:
PersonModel.find({ favouriteFoods: "sushi" }, ...); // favouriteFoods contains "sushi"
But I'd also recommend making the string array explicit in your schema:
person = {
name : String,
favouriteFoods : [String]
}
The relevant documentation can be found here: https://docs.mongodb.com/manual/tutorial/query-arrays/

There is no $contains operator in mongodb.
You can use the answer from JohnnyHK as that works. The closest analogy to contains that mongo has is $in, using this your query would look like:
PersonModel.find({ favouriteFoods: { "$in" : ["sushi"]} }, ...);

I feel like $all would be more appropriate in this situation. If you are looking for person that is into sushi you do :
PersonModel.find({ favoriteFood : { $all : ["sushi"] }, ...})
As you might want to filter more your search, like so :
PersonModel.find({ favoriteFood : { $all : ["sushi", "bananas"] }, ...})
$in is like OR and $all like AND. Check this : https://docs.mongodb.com/manual/reference/operator/query/all/

In case that the array contains objects for example if favouriteFoods is an array of objects of the following:
{
name: 'Sushi',
type: 'Japanese'
}
you can use the following query:
PersonModel.find({"favouriteFoods.name": "Sushi"});

In case you need to find documents which contain NULL elements inside an array of sub-documents, I've found this query which works pretty well:
db.collection.find({"keyWithArray":{$elemMatch:{"$in":[null], "$exists":true}}})
This query is taken from this post: MongoDb query array with null values
It was a great find and it works much better than my own initial and wrong version (which turned out to work fine only for arrays with one element):
.find({
'MyArrayOfSubDocuments': { $not: { $size: 0 } },
'MyArrayOfSubDocuments._id': { $exists: false }
})

Incase of lookup_food_array is array.
match_stage["favoriteFoods"] = {'$elemMatch': {'$in': lookup_food_array}}
Incase of lookup_food_array is string.
match_stage["favoriteFoods"] = {'$elemMatch': lookup_food_string}

Though agree with find() is most effective in your usecase. Still there is $match of aggregation framework, to ease the query of a big number of entries and generate a low number of results that hold value to you especially for grouping and creating new files.
PersonModel.aggregate([
{
"$match": {
$and : [{ 'favouriteFoods' : { $exists: true, $in: [ 'sushi']}}, ........ ] }
},
{ $project : {"_id": 0, "name" : 1} }
]);

There are some ways to achieve this. First one is by $elemMatch operator:
const docs = await Documents.find({category: { $elemMatch: {$eq: 'yourCategory'} }});
// you may need to convert 'yourCategory' to ObjectId
Second one is by $in or $all operators:
const docs = await Documents.find({category: { $in: [yourCategory] }});
or
const docs = await Documents.find({category: { $all: [yourCategory] }});
// you can give more categories with these two approaches
//and again you may need to convert yourCategory to ObjectId
$in is like OR and $all like AND. For further details check this link : https://docs.mongodb.com/manual/reference/operator/query/all/
Third one is by aggregate() function:
const docs = await Documents.aggregate([
{ $unwind: '$category' },
{ $match: { 'category': mongoose.Types.ObjectId(yourCategory) } }
]};
with aggregate() you get only one category id in your category array.
I get this code snippets from my projects where I had to find docs with specific category/categories, so you can easily customize it according to your needs.

For Loopback3 all the examples given did not work for me, or as fast as using REST API anyway. But it helped me to figure out the exact answer I needed.
{"where":{"arrayAttribute":{ "all" :[String]}}}

In case You are searching in an Array of objects, you can use $elemMatch. For example:
PersonModel.find({ favoriteFoods : { $elemMatch: { name: "sushiOrAnytthing" }}});

With populate & $in this code will be useful.
ServiceCategory.find().populate({
path: "services",
match: { zipCodes: {$in: "10400"}},
populate: [
{
path: "offers",
},
],
});

If you'd want to use something like a "contains" operator through javascript, you can always use a Regular expression for that...
eg.
Say you want to retrieve a customer having "Bartolomew" as name
async function getBartolomew() {
const custStartWith_Bart = await Customers.find({name: /^Bart/ }); // Starts with Bart
const custEndWith_lomew = await Customers.find({name: /lomew$/ }); // Ends with lomew
const custContains_rtol = await Customers.find({name: /.*rtol.*/ }); // Contains rtol
console.log(custStartWith_Bart);
console.log(custEndWith_lomew);
console.log(custContains_rtol);
}

I know this topic is old, but for future people who could wonder the same question, another incredibly inefficient solution could be to do:
PersonModel.find({$where : 'this.favouriteFoods.indexOf("sushi") != -1'});
This avoids all optimisations by MongoDB so do not use in production code.

reduce mongo db query to pure array

when i run db.abhishek.em.find({}) I have
{ "_id" : ObjectId("5ac62d35b075e574b3e7eeaa"), "name" : "first", "employed" : true }
{ "_id" : ObjectId("5ac62d3fb075e574b3e7eeab"), "name" : "second", "employed" : true }
{ "_id" : ObjectId("5ac62d4eb075e574b3e7eeac"), "name" : "third", "employed" : false }
I want to reduce this result into an array of simple object ids like this by adding or chaining something to find function , something like
db.a.b.find({employed:true}).somefunction() which can return the below array
I want to use the command nested with $in in a bigger query to achieve some sort of relational querying
[
ObjectId("5ac62d35b075e574b3e7eeaa"),
ObjectId("5ac62d3fb075e574b3e7eeab")
]
-----------------EDIT----------------------
For an example case I want to get employed employees by running
db.abhishek.another.find({id:{$in:db.abhishek.em.find({employed:true},{_id:1}).toArray()}})
or something similiar as this command is not working
The db.a.another collection is
{ "_id" : ObjectId("5ac63de1b075e574b3e7eead"), "id" : ObjectId("5ac62d35b075e574b3e7eeaa"), "name" : "Lets say person 1" }
{ "_id" : ObjectId("5ac63df7b075e574b3e7eeae"), "id" : ObjectId("5ac62d3fb075e574b3e7eeab"), "name" : "Lets say person 2" }
{ "_id" : ObjectId("5ac63e06b075e574b3e7eeaf"), "id" : ObjectId("5ac62d4eb075e574b3e7eeac"), "name" : "Lets say person 3" }
-----------------EDIT----------------------
Solved see my answer below

Use MongoDB to only provide those fields from the model. In MongoDB terms this is called Projection. There is a MongoDB method .project() that you can chain onto your query like this:
db.abhishek.em.find({}).project({});
that should do it. If you want to explicit exclude fields, you do:
db.abhishek.em.find({}).project({name:0, employed:0});
then, finally, to get the output in array form do:
db.abhishek.em.find({}).project({name:0, employed:0}).toArray();
Reference here:
https://docs.mongodb.com/manual/tutorial/project-fields-from-query-results/

Thanks everyone for providing directions and suggestions to move forward,
I was able to successfully do some sort of relational based query using the following
db.abhishek.another.find({id:{$in:db.abhishek.em.find({employed:true},{_id:1}).map(function(e) {return e._id})}},{name:1,_id:0})
It gave this as output
{ "name" : "Lets say person 1" }
{ "name" : "Lets say person 2" }
This query took all records from em collection with employed set to true,form its array and then pass it to $in operator on query for "another" collection to give output
toArray method used to convert objects nested in array hence failing $in operator
Thanks #veeram for telling about selection of fields

how to push a dictionary to a nested array with mongodb?

i have data that looks like this in my database
> db.whocs_up.find()
{ "_id" : ObjectId("52ce212cb17120063b9e3869"), "project" : "asnclkdacd", "users" : [ ] }
and i tried to add to the 'users' array like thus:
> db.whocs_up.update({'users.user': 'usex', 'project' : 'asnclkdacd' },{ '$addToSet': { 'users': {'user':'userx', 'lastactivity' :2387843543}}},true)
but i get the following error:
Cannot apply $addToSet modifier to non-array
same thing happens with push operator, what im i doing wrong?
im on 2.4.8
i tried to follow this example from here:
MongoDB - Update objects in a document's array (nested updating)
db.bar.update( {user_id : 123456, "items.item_name" : {$ne : "my_item_two" }} ,
{$addToSet : {"items" : {'item_name' : "my_item_two" , 'price' : 1 }} } ,
false ,
true)
the python tag is because i was working with python when i ran into this, but it does nto work on the mongo shell as you can see
EDIT ============================== GOT IT TO WORK
apparently if i modify the update from
db.whocs_up.update({'users.user': 'usex', 'project' : 'asnclkdacd' },{ '$addToSet': { 'users': {'user':'userx', 'lastactivity' :2387843543}}},true)
to this:
db.whocs_up.update({'project' : 'asnclkdacd' },{ '$addToSet': { 'users': {'user':'userx', 'lastactivity' :2387843543}}},true)
it works, but can anyone explain why the two do not achieve the same thing, in my understanding they should have referenced the same document and hence done the same thing,
What does the addition of 'users.user': 'userx' change in the update? does it refer to some inner document in the array rather than the document as a whole?

This is a known bug in MongoDB (SERVER-3946). Currently, an update with $push/$addToSet with a query on the same field does not work as expected.
In the general case, there are a couple of workarounds:
Restructure your update operation to not have to query on a field that is also to be updated using $push/$addToSet (as you have done above).
Use the $all operator in the query, supplying a single-value array containing the lookup value. e.g. instead of this:
db.foo.update({ x : "a" }, { $addToSet : { x : "b" } }, true)
do this:
db.foo.update({ x : { $all : ["a"] } }, { $addToSet : { x : "b" } } , true)
In your specific case, I think you need to re-evaluate the operation you're trying to do. The update operation you have above will add a new array entry for each unique (user, lastactivity) pair, which is probably not what you want. I assume you want a unique entry for each user.
Consider changing your schema so that you have one document per user:
{
_id : "userx",
project : "myproj",
lastactivity : 123,
...
}
The update operation then becomes something like:
db.users.update({ _id : "userx" }, { $set : { lastactivity : 456 } })
All users in a given project may still be looked up efficiently by adding a secondary index on project.
This schema also avoids the unbounded document growth of the above schema, which is better for performance.

Mongo query in nested fields

I have a DB which has records with nested fields like :
"requestParams" : { "query" : [ "tv9" ] }
I am using the following query to fetch these kind of records. However I am looking for a more general case wherein the field query matches /tv9/ which includes tv9 as part of any search. Like it should also return livetv9, movietv9, etc. Following query does not seem to work:
db.requestLog.findOne({url : /search.json/, requestParams: {$elemMatch: {query: /tv9/}}})

$elemMatch is used to match partial document elements inside an array. Since you want to directly match on a string the use of this operator is inappropriate. Use this instead :
db.requestLog.findOne({url : /search.json/, 'requestParams.query': /tv9/})
Example :
mongos> db.test.save({r:{q:["tv9"]}})
mongos> db.test.save({r:{q:["tv"]}})
mongos> db.test.save({r:{q:["ltv9l"]}})
mongos> db.test.find({'r.q':/tv9/})
{ "_id" : ObjectId("4f5095d4ec991a74c16ba862"), "r" : { "q" : [ "tv9" ] } }
{ "_id" : ObjectId("4f5095deec991a74c16ba864"), "r" : { "q" : [ "ltv9l" ] } }