I wonder if there is a way to get a single object instead of an array when querying for a single embedded document in MongoDB
I have Groups with embedded Users
{
groupname: "Admins",
users: [
{
email: bob#google.com,
first_name: 'bob'
},
{...},
{...} // multiple embedded users
]
}
I can query a single user from a group with this query
db.groups.find({'users.email' => bob#google.com}, {'users.$' => 1})
but it gives me a 'users' array with 1 user init
{
groupname: "Admins",
users: [
{
email: bob#google.com,
first_name: 'bob'
}
]
}
then I have to select the first element in the array,
users[0]
there is no problem with it, but then i just have to write more code in my application, the better way should be
user (-s)
so I can query
user.first_name
if someone knows a way let me know
You can use findOne as it returns a single document, where find returns a cursor.
>user = db.groups.findOne({'users.email' : bob#google.com}, {'users.$' => 1})
>user.first_name
Depending from the driver you are using findOne is deprecated, you should use find().limit(1).next(function(err, doc){})
http://mongodb.github.io/node-mongodb-native/2.0/api/Collection.html#findOne
Related
I'm going around in circles with this one so hoping someone can help. I'm building a nodejs application that receives sensor values from nodes. There can be multiple sensors on a node.
Using NodeJS, Mongod DB and Mongoose, all running on a raspberry pi, 3 I've built the following Schemas & Model:
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var valueSchema = new Schema ({
timestamp: {type: Date},
value: {}
});
var sensorSchema = new Schema ({
id: {type: Number},
type: {type: String},
description: {type: String},
ack: {type: Boolean},
values: [valueSchema]
});
var SensorNode = mongoose.model('SensorNode', {
id: {type: Number, required: true},
protocol: {},
sensors: [sensorSchema]
});
I can add in the node, and push sensors onto the sensors array, but I seem unable to push values onto the values array.
I've looked over a few other examples and questions on similar issues, and looked at using populate, but cant seem to get them to work.
Here is my code:
function saveValue(rsender, rsensor, payload) {
var value = {
values: {
timestamp: new Date().getTime(),
value: payload
}
}
SensorNode.findOneAndUpdate({
"id": rsender,
"sensors.id": rsensor
}, {
"$push": {
"sensors.$": value
}
}, function(err, result) {
if (err) {
console.log(err);
}
console.log(result);
});
}
This is returning undefined for the result and this error:
MongoError: exception: Cannot apply $push/$pushAll modifier to non-array
Values is definitely an array in the sensor schema.
I'm using readable ids rather than the auto assigned Mongo DB IDs for the sake of the UI, but I could use the MongoDB _id if that makes any difference, I don't see why it would?
Where am I going wrong ?
You're using positional operator $ so let's check the docs
The positional $ operator identifies an element in an array to update without explicitly specifying the position of the element in the array. To project, or return, an array element from a read operation, see the $ projection operator.
So sensors.$ will return one particular document from your sensors array. That's why you're getting an error. On this level of your document you can only replace this item by using $set. I bet you wanted to do something like this:
SensorNode.findOneAndUpdate({
"id": rsender,
"sensors.id": rsensor
}, {
"$push": {
"sensors.$.values": payload
}
});
This operation will just append payload to values array in one particular sensor with id equal to rsensor.
I have a collection Playlist that contains an array of items
{
userId: {
type : String,
required : true,
index : true,
unique : true
},
items: [
{
id: { // do not mix up with _id, which is the autogenerated id of the pair {id,type}. ID is itemId
type : Schema.Types.ObjectId
},
type: {
type : String
}
}
]
}
Mongo automatically adds the _id field to the items when I push a pair {id,type} to items (but I don't care about it).
Now I would like to remove several "pairs" at once from the items array.
I have tried using $pullAll but it requires an exact match, and I do not know the _id, so it does not remove anything from items
playlistModel.update({userId:userId},{$pullAll:{items:[{id:"123",type:"video"},{id:"456",type:"video"}]}},null,function(err){
I have tried using $pull with different variants, but it removed ALL objects from items
playlistModel.update({userId:userId},{$pull:{items:{"items.id":{$in:["123","456"]}}}},null,function(err){
playlistModel.update({userId:userId},{$pull:{items:{$in:[{id:"123",type:"video"},{id:"456",type:"video"}]}}},null,function(err){
Am I missing something or am I asking something that isn't implemented?
If the latter, is there a way I can go around that _id issue?
OK I found a way that works using $pull:
playlistModel.update({userId:userId},{$pull:{items:{id:{$in:["123","456"]}}}},null,function(err){
It doesn't take the type into account but I can't see any issue with that since the id is unique across all types anyway.
Although I will wait a bit to see if someone has a better solution to offer
EDIT
With Veeram's help I got to this other solution, which IMO is more elegant because I don't have _ids that I don't need in the database, and the $pullAll option seems more correct here
var playlistItemSchema = mongoose.Schema({
id: { // do not mix up with autogenerated _id. id is itemId
type : Schema.Types.ObjectId
},
type: {
type : String
}
},{ _id : false });
var schema = new Schema({
userId: {
type : String,
required : true,
index : true,
unique : true
},
items: [playlistItemSchema]
});
playlistModel.update({userId:userId},{$pullAll:{items:[{id:"123",type:"video"},{id:"456",type:"video"}]}},null,function(err){
tips:
you can use _id field to handle your playlistModel data.
mongoose api : new mongoose.Types.ObjectId to generate an Object_id
let _id=new mongoose.Types.ObjectId;
playlistModel.updateMany({_id:_id},{ $set: { name: 'bob' }}).exec(data=>{console.log('exec OK')});
How could I find an image by id in this Schema. I have the id of the User and the id of the image I am looking for. What would be the best way to do this and do all images in this case have different ids or could they have the same id because they don't belong to the same User?
My Schema looks like this:
var userSchema = new Schema({
local: {
email: String,
password: String
},
facebook: {
id: String,
token: String,
email: String,
name: String
},
name: String,
about: String,
images: [{
id: Schema.ObjectId,
link: String,
main: Boolean
}]
});
When you are interested in the full object it is a simple find:
.find({"facebook.id":"<id>", "images.id":<image-id>})
I don't think that there is a way to reduce the image array in the result.
To update a single element in the image array you can use this:
.update({"facebook.id":"<id>", "images.id":<image-id>}, {$set : {"images.$.main" :false} } );
userSchema .find({facebook.id: "some ID",{ "images.id": { $in: [ id1, id2, ...idn] }}
since images are inside the document you can have same ID's however every time you query you should keep in mind that you send some other parameters such as facebook.id or facebook.email along with image id's to retrieve them. Otherwise you end up getting all that might be irrelevant only because you decide to keep same ID's for images.
tl;dr
I struggled with this and came up with a solution. Like you, I was trying to query for a deeply nested object by the _id, but I kept coming up empty with the results. It wasn't until I did some type checking that I realized the id value I was getting from my frontend, while directly supplied by mongoose, was in fact a String and not an Object.
I realize this question was already partially answered before, but that person's solution didn't work for me, and the comment on the answer tells me you wanted to update the specific image you queried for, which is exactly what I was trying to do.
The solution
In order to select an object from the nested array by the _id value, first you'll have to install the npm package bson-objectid and use the provided method to convert your string into an objectId in your query.
In your terminal:
npm i bson-objectid
In your code:
const ObjectId = require('bson-objectid')
userSchema.findOneAndUpdate(
{ "facebook.id": <user-id>, "images._id": ObjectId(<image-id>) },
{ "$set": { "images.$.main": false } },
{ new: true }, // an extra options parameter that returns the mutated document
(err, user) => {
if (err) {
handleErr(err)
} else {
console.log(user)
// do something with new user info
}
)
My firebase users tree has this structure:
users:
{
{
'userName': 'abc',
'userEmail' : 'abc#abc.com',
'userPreferences':
[
0:'Cinema',
1:'It'
]
},
{
'userName': 'abc',
'userEmail' : 'abc#abc.com',
'userPreferences':
[
0:'Cinema',
1:'Music'
]
}
}
Then, I try to find all users that their preference list contain 'Cinema'.
I try this code:
var ref1 = new Firebase("https://event-application.firebaseio.com/users");
$scope.user = $firebaseArray(ref1.orderByChild("userpreferences").equalTo('Cinema'));
console.log($scope.user);
But I don't get the best result. I get this record:
Your JSON structure shows preferences as userPreferences, so wouldn't the following work?
var ref1 = new Firebase("https://event-application.firebaseio.com/users");
$scope.user = $firebaseArray(ref1.orderByChild("userPreferences").equalTo('Cinema'));
console.log($scope.user);
However I think there is also another problem with your code, you're called an .equalTo('Cinema') however you're comparing it to an array, correct me if i'm wrong but I don't think the behaviour of .equalTo('Cinema') is to loop through each of the values and compare them, I think it's just a straight up comparison
If this is the case, you may need to build a custom query by reading the data from firebase and manipulating it via function available to a snapshot
In NoSQL you'll often end up with a data model that reflects the way your application uses the data. If you want to read all the users that have a preference for Cinema, you should model that in your tree:
users: {
'uid-of-abc': {
'userName': 'abc',
'userEmail' : 'abc#abc.com',
'userPreferences': [
0:'Cinema',
1:'It'
]
},
'uid-of-def': {
'userName': 'def',
'userEmail' : 'abc#abc.com',
'userPreferences': [
0:'Cinema',
1:'Music'
]
}
},
"preferences-lookup": {
"Cinema": {
"uid-of-abc": true,
"uid-of-def": true
},
"It": {
"uid-of-abc": true
},
"Music": {
"uid-of-def": true
}
}
Now you can find out what users prefer cinema with:
ref.child('preferences-lookup/Cinema').on('value', function(snapshot) {
snapshot.forEach(function(userKey) {
console.log(userKey.key()+' prefers Cinema');
});
});
This is covered in this blog post on denormalizing data with Firebase, in the Firebase documentation on structuring data and in dozens of answers here on Stack Overflow. A few:
Storing Relational "Type" or "Category" Data in Firebase Without the Need to Update Multiple Locations
Get Firebase items belonging to category
Retrieve data based on categories in Firebase
How to query firebase for property with specific value inside all children
I have a document in mongodb with 2 level deep nested array of objects that I need to update, something like this:
{
id: 1,
items: [
{
id: 2,
blocks: [
{
id: 3
txt: 'hello'
}
]
}
]
}
If there was only one level deep array I could use positional operator to update objects in it but for second level the only option I've came up is to use positional operator with nested object's index, like this:
db.objects.update({'items.id': 2}, {'$set': {'items.$.blocks.0.txt': 'hi'}})
This approach works but it seems dangerous to me since I'm building a web service and index number should come from client which can send say 100000 as index and this will force mongodb to create an array with 100000 indexes with null value.
Are there any other ways to update such nested objects where I can refer to object's ID instead of its position or maybe ways to check if supplied index is out of bounds before using it in query?
Here's the big question, do you need to leverage Mongo's "addToSet" and "push" operations? If you really plan to modify just individual items in the array, then you should probably build these arrays as objects.
Here's how I would structure this:
{
id: 1,
items:
{
"2" : { "blocks" : { "3" : { txt : 'hello' } } },
"5" : { "blocks" : { "1" : { txt : 'foo'}, "2" : { txt : 'bar'} } }
}
}
This basically transforms everything in to JSON objects instead of arrays. You lose the ability to use $push and $addToSet but I think this makes everything easier. For example, your query would look like this:
db.objects.update({'items.2': {$exists:true} }, {'$set': {'items.2.blocks.0.txt': 'hi'}})
You'll also notice that I've dumped the "IDs". When you're nesting things like this you can generally replace "ID" with simply using that number as an index. The "ID" concept is now implied.
This feature has been added in 3.6 with expressive updates.
db.objects.update( {id: 1 }, { $set: { 'items.$[itm].blocks.$[blk].txt': "hi", } }, { multi: false, arrayFilters: [ { 'itm.id': 2 }, { 'blk.id': 3} ] } )
The ids which you are using are linear number and it has to come from somewhere like an additional field such 'max_idx' or something similar.
This means one lookup for the id and then update. UUID/ObjectId can be used for ids which will ensure that you can use Distributed CRUD as well.
Building on Gates' answer, I came up with this solution which works with nested object arrays:
db.objects.updateOne({
["items.id"]: 2
}, {
$set: {
"items.$.blocks.$[block].txt": "hi",
},
}, {
arrayFilters: [{
"block.id": 3,
}],
});
MongoDB 3.6 added all positional operator $[] so if you know the id of block that need update, you can do something like:
db.objects.update({'items.blocks.id': id_here}, {'$set': {'items.$[].blocks.$.txt': 'hi'}})
db.col.update({"items.blocks.id": 3},
{ $set: {"items.$[].blocks.$[b].txt": "bonjour"}},
{ arrayFilters: [{"b.id": 3}] }
)
https://docs.mongodb.com/manual/reference/operator/update/positional-filtered/#update-nested-arrays-in-conjunction-with
This is pymongo function for find_one_and_update. I searched a lot to find the pymongo function. Hope this will be useful
find_one_and_update(filter, update, projection=None, sort=None, return_document=ReturnDocument.BEFORE, array_filters=None, hint=None, session=None, **kwargs)
Example
db.pymongo_object.find_one_and_update( filter = {'id' : 1}, update= {$set: {"items.$[array1].blocks.$[array2].txt": "hi"}}, array_filters =[{"array1.id" :2}, {"array2.id": 3}])
Also see pymongo documentation.