Suppose I have the following schema:
{
_id: ObjectId(1),
title: string,
answers: [
{
_id: ObjectId(2),
text: string,
upVotes: [
{
_id: ObjectId(3),
userId: ObjectId(4)
}
]
}
]
}
What I want is pull vote of a specific user from answer upvotes, and return the new update result.
For example, find a question with id 1, and get its specific answer with id 2, then from that answer pull my vote using userId inside upvotes.
I want to do it with a single findOneAndUpdate query
You can even use single $ positional with the $pull operator to update the nested array
db.collection.findOneAndUpdate(
{ "_id": ObjectId(1), "answers._id": ObjectId(2) },
{ "$pull": { "answers.$.upVotes": { "userId": ObjectId(4) }}}
)
I think I understood that you want to do a search in the specific array
db.collection.update(
{
"_id": "507f1f77bcf86cd799439011", // id field
"answers.upVotes._id":"507f1f77bcf86cd799439011" //id array
}
),{
"$set":{"answers.$.upVotes": {userId :"507f1f77bcf86cd799439011"}}},//edit
//use "addToSet" for add
Related
This has been extensively covered here, but none of the solutions seems to be working for me. I'm attempting to remove an object from an array using that object's id. Currently, my Schema is:
const scheduleSchema = new Schema({
//unrelated
_id: ObjectId
shifts: [
{
_id: Types.ObjectId,
name: String,
shift_start: Date,
shift_end: Date,
},
],
});
I've tried almost every variation of something like this:
.findOneAndUpdate(
{ _id: req.params.id },
{
$pull: {
shifts: { _id: new Types.ObjectId(req.params.id) },
},
}
);
Database:
Database Format
Within these variations, the usual response I've gotten has been either an empty array or null.
I was able slightly find a way around this and accomplish the deletion by utilizing the main _id of the Schema (instead of the nested one:
.findOneAndUpdate(
{ _id: <main _id> },
{ $pull: { shifts: { _id: new Types.ObjectId(<nested _id>) } } },
{ new: true }
);
But I was hoping to figure out a way to do this by just using the nested _id. Any suggestions?
The problem you are having currently is you are using the same _id.
Using mongo, update method allows three objects: query, update and options.
query object is the object into collection which will be updated.
update is the action to do into the object (add, change value...).
options different options to add.
Then, assuming you have this collection:
[
{
"_id": 1,
"shifts": [
{
"_id": 2
},
{
"_id": 3
}
]
}
]
If you try to look for a document which _id is 2, obviously response will be empty (example).
Then, if none document has been found, none document will be updated.
What happens if we look for a document using shifts._id:2?
This tells mongo "search a document where shifts field has an object with _id equals to 2". This query works ok (example) but be careful, this returns the WHOLE document, not only the array which match the _id.
This not return:
[
{
"_id": 1,
"shifts": [
{
"_id": 2
}
]
}
]
Using this query mongo returns the ENTIRE document where exists a field called shifts that contains an object with an _id with value 2. This also include the whole array.
So, with tat, you know why find object works. Now adding this to an update query you can create the query:
This one to remove all shifts._id which are equal to 2.
db.collection.update({
"shifts._id": 2
},
{
$pull: {
shifts: {
_id: 2
}
}
})
Example
Or this one to remove shifts._id if parent _id is equal to 1
db.collection.update({
"_id": 1
},
{
$pull: {
shifts: {
_id: 2
}
}
})
Example
"ID": 254252324242423
"objList" : [{
"Date":3-6-2013,
"Times": ["16:34-17:54", "18:00-19:00"]
},{
"Date":3-7-2013,
"Times": ["16:34-17:54", "18:23-19:00"]
},{
"Date":3-8-2013,
"Times": ["16:34-17:54", "18:30-20:00"]
}]
I don't know how to add an element to the array of an object from the list with a specific date.
this is a way i have found
Two possibilities here:
Since you don't have an unique identifier for the comments, the only way to update an specific item on the comments array is to explicitly indicate the index you are updating, like this:
db.documents.update(
{ _id: "iL9hL2hLauoSimtkM"},
{ $push: { "comments.0.likes": "userID3" }}
);
If you add an unique identifier for the comments, you can search it and update the matched item, without worrying with the index:
db.documents.update(
{ _id: "iL9hL2hLauoSimtkM", "comments._id": "id1"},
{ $push: { "comments.$.likes": "userID3" }}
);
This question already has answers here:
Retrieve only the queried element in an object array in MongoDB collection
(18 answers)
Closed 3 years ago.
In my situation I just need my result but without my objectID in my array.
This is my method :
return Room.findOne(
{
_id: idRoom,
participants: {$elemMatch: {$ne: this.currentUser.profile}},
},
{
'participants.$': 1,
}
)
With elementMatch, the problem is when you found the object, only the first object is returned.
This is my result :
"result": {
"_id": "5da5e77f51e08708b79565e8",
"participants": [
"5da4d5b40cc94f04a7aaad40"
],
And this is the real result I need
"result": {
"_id": "5da5e77f51e08708b79565e8",
"participants": [
"5da4d5b40cc94f04a7aaad40"
"fwnert9248yrhnqwid13982r" // I have another participants
],
And my model is just like this :
const RoomSchema = new Schema({
participants: [{type: Schema.Types.ObjectId,ref: 'Profile'}],
...
}, options)
For others reasons, I can't use aggregate, thank you if you have the solution
So I think you are trying to shape a resultset in mongo with the findOne() method, and any use of the aggregation pipeline framework is out of the question and unavailable for other reasons.
I am not sure this is possible. I believe you will need to perform multiple steps to achieve your desired results. If you can use aggregation pipeline framework here is a pipeline to suit the desired results (I believe)...
db.Room.aggregate(
[
{
"$match": { _id: ObjectId(idRoom)}
},
{
$project: {
"participants": {
$filter: {
input: "$participants",
as: "participant",
cond: {$ne: ["$$participant", this.currentUser.profile] }
}
}
}
}
]
)
...but if you cannot use aggregation pipeline then here is a mongoshell script that accomplishes the task in several steps. The strategy is to capture the whole document by _id then remove the data element from the array then echo the results...
var document = db.Room.findOne( { _id: ObjectId("5da64a62cd63abf99d11f210") } );
document.participants.splice(document.participants.indexOf("5da4d5b40cc94f04a7aaad40"), 1);
document;
Consider the following posts collection:
{
_id: 1,
title: "Title1",
category: "Category1",
comments: [
{
title: "CommentTitle1",
likes: 3
},
{
title: "CommentTitle2",
likes: 4
}
]
}
{
_id: 2,
title: "Title2",
category: "Category2",
comments: [
{
title: "CommentTitle3",
likes: 1
},
{
title: "CommentTitle4",
likes: 4
}
]
}
{
_id: 3,
title: "Title3",
category: "Category2",
comments: [
{
title: "CommentTitle5",
likes: 1
},
{
title: "CommentTitle6",
likes: 3
}
]
}
I want to retrieve all the posts, and if one post has a comment with 4 likes I want to retrieve this comment only under the "comments" array. If I do this:
db.posts.find({}, {comments: { $elemMatch: {likes: 4}}})
...I get this (which is exactly what I want):
{
_id: 1,
comments: [
{
title: "CommentTitle2",
likes: 4
}
]
}
{
_id: 2,
comments: [
{
title: "CommentTitle4",
likes: 4
}
]
}
{
_id: 3
}
But how can I retrieve the remaining fields of the documents without having to declare each of them like below? This way if added more fields to the post document, I wouldn't have to change the find query
db.posts.find({}, {title: 1, category: 1, comments: { $elemMatch: {likes: 4}}})
Thanks
--EDIT--
Sorry for the misread of your question. I think you'll find my response to this question here to be what you are looking for. As people have commented, you cannot project this way in a find, but you can use aggregation to do so:
https://stackoverflow.com/a/21687032/2313887
The rest of the answer stands as useful. So I think I'll leave it here
You must specify all of the fields you want or nothing at all when using projection.
You are asking here essentially that once you choose to alter the output of the document and limit how one field is displayed then can I avoid specifying the behavior. The bottom line is thinking of the projection part of a query argument to find just like SQL SELECT.It behaves in that * or all is the default and after that is a list of fields and maybe some manipulation of the fields format. The only difference is for _id which is always there by default unless specified otherwise by excluding it, i.e { _id: 0 }
Alternately if you want to filter the collection you nee to place your $elemMatch in thequery itself. The usage here in projection is to explicitly limit the returned document to only contain the matching elements in the array.
Alter your query:
db.posts.find(
{ comments: { $elemMatch: {likes: 4}}},
{ title: 1, category: 1, "comments.likes.$": 1 }
)
And to get what you want we use the positional $ operator in the projection portion of the find.
See the documentation for the difference between the two usages:
http://docs.mongodb.org/manual/reference/operator/query/elemMatch/
http://docs.mongodb.org/manual/reference/operator/projection/elemMatch/
This question is pretty old, but I just faced the same issue and I didn't want to use the aggregation pipeline as it was simple query and I only needed to get all fields applying an $elemMatch to one field.
I'm using Mongoose (which was not the original question but it's very frequent these days), and to get exactly what the question said (How can I retrieve all the fields when using $elemMatch?) I made this:
const projection = {};
Object.keys(Model.schema.paths).forEach(key => {
projection[key] = 1;
});
projection.subfield = { $elemMatch: { _id: subfieldId } };
Model.find({}, projection).then((result) => console.log({ result });
I have the following data in MongoDB (simplified for what is necessary to my question).
{
_id: 0,
actions: [
{
type: "insert",
data: "abc, quite possibly very very large"
}
]
}
{
_id: 1,
actions: [
{
type: "update",
data: "def"
},{
type: "delete",
data: "ghi"
}
]
}
What I would like is to find the first action type for each document, e.g.
{_id:0, first_action_type:"insert"}
{_id:1, first_action_type:"update"}
(It's fine if the data structured differently, but I need those values present, somehow.)
EDIT: I've tried db.collection.find({}, {'actions.action_type':1}), but obviously that returns all elements of the actions array.
NoSQL is quite new to me. Before, I would have stored all this in two tables in a relational database and done something like SELECT id, (SELECT type FROM action WHERE document_id = d.id ORDER BY seq LIMIT 1) action_type FROM document d.
You can use $slice operator in projection. (but for what you do i am not sure that the order of the array remain the same when you update it. Just to keep in mind))
db.collection.find({},{'actions':{$slice:1},'actions.type':1})
You can also use the Aggregation Pipeline introduced in version 2.2:
db.collection.aggregate([
{ $unwind: '$actions' },
{ $group: { _id: "$_id", first_action_type: { $first: "$actions.type" } } }
])
Using the $arrayElemAt operator is actually the most elegant way, although the syntax may be unintuitive:
db.collection.aggregate([
{ $project: {first_action_type: {$arrayElemAt: ["$actions.type", 0]}
])