I am new in nodejs. I want below result but it shows last value.
"child_skills" : [
"Nodejs",
"Android",
"Javascript"
],
My nodejs method
export function create(req, res) {
return JobCategories.create(req.body)
.then((JobCategoryInstance) => {
var childskill = [];
for (var i = 0; i < JobCategoryInstance.child_categories.length; i++) {
childskill = JobCategoryInstance.child_categories[i].child_categoryname;
}
EngineerSkills.create({ skill_name: JobCategoryInstance.category_name, child_skills: childskill });
return JobCategoryInstance;
})
.then(respondWithResult(res, 201))
.catch(handleError(res));
}
My result is below. Why this is get only last value?
{
"_id" : ObjectId("58c2d5019caa49199854872e"),
"skill_name" : "soft",
"date_updated" : ISODate("2017-03-10T16:32:01.437Z"),
"child_skills" : [
"Javascript"
],
"__v" : 0
}
Instead of adding elements to the array, you are substituting the array with one of the elements every time.
Change this:
childskill = JobCategoryInstance.child_categories[i].child_categoryname;
to this:
childskill.push(JobCategoryInstance.child_categories[i].child_categoryname);
if you want new elements to be added to the array every time.
Related
I have a mongoose schema of mixed types like so:
const user = mongoose.Schema({
...
"links" : []
...
After populating this schema, I ended up with data like so:
[
[
{
"step1": "post-url-google", // This field is unique for each entry
"step2": {
"title": "Heading 1",
"likes": 4
}
},
],
[
{
"step1": "post-url-microsoft",
"step2": {
"title": "Heading 1",
"likes": 1
}
},
{
"step1": "post-url-apple",
"step2": {
"title": "Heading 2",
"likes": 6 // I want to update this to 7
}
}
]
]
What I want to achieve is to update the "step1": "post-url-apple" field from 6 to have a likes of 7
So I tried using the User.save() function like so:
let user = await User.findOne({"_id" : "some_id"})
user.links[1].some(object => {
if (object.step1 === "post-url-apple") {
object.step2.likes = 7
(async function (){
user.save() // I also did error handling
})()
return
}
})
This method works fine and the user gets updated but it keeps throwing ParallelSaveError possibly because I am calling the save() function in parallel on the same user instance in some other parts of my code.
So I decided to use the User.findOneAndUpdate() method, but my queries keep failing when using the mongodb dot notation $[<identifier>], obviously because I don't know how to use it properly.
Like so:
let update = {
"$set" : {
"links.$[index1].$[index2].step2.likes" : 7,
}
}
let conditions = {
arrayFilters : [
{"index1" : 1},
{"index2.step1" : "post-url-apple"}
]
}
try {
let result = await Users.findOneAndUpdate({"_id" : "some_id"}, update, conditions)
console.log(result)
} catch (err) {
console.log(err)
}
For all good reasons, I'm not hiting the catch block but the update was equally not successful
How do I achieve updating the "step1": "post-url-apple" likes field to 7 using findOneAndUpdate?
Thank you.
In arrayFilters you should define the conditions to be applied to all the array elements, not the index
If you are sure, you always update the second array element (index = 1) of the outer array, then you can use the dot notation for the outer array, and for the inner array you can use the array filters to get the element that has step1 = 'post-url-apple'
your code may look something like that
let update = {
"$set" : {
'links.1.$[item].step2.likes': 7 // here we used links.1 to access the second element of the outer array
}
}
let conditions = {
arrayFilters : [
{ 'item.step1' : 'post-url-apple' } // item here is the element in the inner array that has step1 = post-url-apple
]
}
then do your update query
hope it helps
Desired Behaviour
Pull a range of objects from an array of objects and push them back to the array at a new index.
For example, pull objects from the array where their index is between 0 and 2, and push them back to the array at position 6.
For reference, in jQuery, the desired behaviour can be achieved with:
if (before_or_after === "before") {
$("li").eq(new_position).before($("li").slice(range_start, range_end + 1));
} else if (before_or_after === "after") {
$("li").eq(new_position).after($("li").slice(range_start, range_end + 1));
}
jsFiddle demonstration
Schema
{
"_id": ObjectId("*********"),
"title": "title text",
"description": "description text",
"statements": [
{
"text": "string",
"id": "********"
},
{
"text": "string",
"id": "********"
},
{
"text": "string",
"id": "********"
},
{
"text": "string",
"id": "********"
},
{
"text": "string",
"id": "********"
}]
}
What I've Tried
I am able to reposition a single object in an array of objects with the code below.
It uses pull to remove the object from the array and push to add it back to the array at a new position.
In order to do the same for a range of objects, I think I just need to modify the $pull and $push variables but:
I can't figure out how to use $slice in this context, either as a projection or an aggregation, in a $pull operation
Because I can't figure out the first bit, I don't know how to attempt the second bit - the $push operation
// define the topic_id to search for
var topic_id = request_body.topic_id;
// make it usable as a search query
var o_id = new ObjectID(topic_id);
// define the statement_id to search for
var statement_id = request_body.statement_id;
// define new position
var new_position = Number(request_body.new_position);
// define old position
var old_position = Number(request_body.old_position);
// define before or after (this will be relevant later)
// var before_or_after = request_body.before_or_after;
// define the filter
var filter = { _id: o_id };
// define the pull update - to remove the object from the array of objects
var pull_update = {
$pull: {
statements: { id: statement_id } // <----- how do i pull a range of objects here
}
};
// define the projection so that only the 'statements' array is returned
var options = { projection: { statements: 1 } };
try {
// perform the pull update
var topic = await collection.findOneAndUpdate(filter, pull_update, options);
// get the returned statement object so that it can be inserted at the desired index
var returned_statement = topic.value.statements[old_position];
// define the push update - to add the object back to the array at the desired position
var push_update = {
$push: {
statements: {
$each: [returned_statement],
$position: new_position
}
} // <----- how do i push the range of objects back into the array here
};
// perform the push update
var topic = await collection.findOneAndUpdate(filter, push_update);
}
Environments
##### local
$ mongod --version
db version v4.0.3
$ npm view mongodb version
3.5.9
$ node -v
v10.16.3
$ systeminfo
OS Name: Microsoft Windows 10 Home
OS Version: 10.0.18363 N/A Build 18363
##### production
$ mongod --version
db version v3.6.3
$ npm view mongodb version
3.5.9
$ node -v
v8.11.4
RedHat OpenShift Online, Linux
Edit
Gradually, figuring out parts of the problem, I think:
Using the example here, the following returns objects from array with index 0 - 2 (ie 3 objects):
db.topics.aggregate([
{ "$match": { "_id": ObjectId("********") } },
{ "$project": { "statements": { "$slice": ["$statements", 0, 3] }, _id: 0 } }
])
Not sure how to use that in a pull yet...
I also looked into using $in (even though i would prefer to just grab a range of objects than have to specify each object's id), but realised it does not preserve the order of the array values provided in the results returned:
Does MongoDB's $in clause guarantee order
Here is one solution to re-ordering results from $in in Node:
https://stackoverflow.com/a/34751295
Here an example with mongo 3.5
const mongo = require('mongodb')
;(async function (params) {
const client = await mongo.connect('mongodb://localhost:27017')
const coll = client.db('test').collection('test')
const from0to99 = Array(100).fill('0').map((_, i) => String(i))
const from5To28 = Array(24).fill('0').map((_, i) => String(i + 5))
const insert = { statements: from0to99.map(_ => ({ id: _ })) }
await coll.insertOne(insert)
const all100ElementsRead = await coll.findOneAndUpdate(
{ _id: insert._id },
{
$pull: {
statements: {
id: { $in: from5To28 }
}
}
},
{ returnOriginal: true }
)
/**
* It shows the object with the desired _id BEFORE doing the $pull
* You can process all the old elements as you wish
*/
console.log(all100ElementsRead.value.statements)
// I use the object read from the database to push back
// since I know the $in condition, I must filter the array returned
const pushBack = all100ElementsRead.value.statements.filter(_ => from5To28.includes(_.id))
// push back the 5-28 range at position 72
const pushed = await coll.findOneAndUpdate(
{ _id: insert._id },
{
$push: {
statements: {
$each: pushBack,
$position: 72 // 0-indexed
}
}
},
{ returnOriginal: false }
)
console.log(pushed.value.statements) // show all the 100 elements
client.close()
})()
This old issue helped
if you want "desired behavior" when mutating arrays ,
you add these to checklist:
array.length atleast==7 if you want to add ,splice at 6
creates a new array if u use concat
mutates orignal if used array.push or splice or a[a.length]='apple'
USE slice() to select between incex1 to index2.
or run a native for loop to select few elements of array or
apply a array.filter() finction.
once you select your elements which needed to be manupulated you mentioned you want to add it to end. so this is the method below.
about adding elements at end:
CONCAT EXAMPLE
const original = ['🦊']; //const does not mean its immutable just that it cant be reassigned
let newArray;
newArray = original.concat('🦄');
newArray = [...original, '🦄'];
// Result
newArray; // ['🦊', '🦄']
original; // ['🦊']
SPLICE EXAMPLE:
const zoo = ['🦊', '🐮'];
zoo.splice(
zoo.length, // We want add at the END of our array
0, // We do NOT want to remove any item
'🐧', '🐦', '🐤', // These are the items we want to add
);
console.log(zoo); // ['🦊', '🐮', '🐧', '🐦', '🐤']
I am storing in my mongodb collection the video id of a video served in the cloud. When my front end makes an API call for that video, I want to return the formatted URL based on that video id. I have a function that does this, but I can't get it to work with $addFields in and aggregate pipeline:
My documents look like this:
{
"date" : ISODate("2018-03-30T00:00:00.000+0000"),
"title" : "Tips and Tricks",
"video_id" : "13966740",
}
...and I want my API call to return them with an extra field, "image_url":
{
"date" : ISODate("2018-03-30T00:00:00.000+0000"),
"title" : "Tips and Tricks",
"video_id" : "13966740",
"image_url" : "https://myhostingservice.com/13966740/preview_image",
}
This is what I'm trying in models/video.js:
const hostingservice = require('myhostingservicehelperfunctions');
module.exports.getVideo = function (callback) {
videoCollection.aggregate(
[
{ $match: { } },
{ $addFields: {
image_url: hostingservice.createImageURL("$video_id")
}
},
{ $sort: {
'date' : -1 }
}
],
callback);
};
The helper function simply takes the string param and returns a string.
myhostingservicehelperfunctions.js:
module.exports.createImageURL = function ImageURL(video_id){
return 'https://myhostingservice.com/' + video_id + '/preview_image';
};
My front end receives all the correct data, but the value of image_url is "https://myhostingservice.com/$video_id/preview_image", which makes me think my function ran, but it was passed the actual string "$video_id", not the value of the key, video_id. Look closely, the URL contains "$video_id", not "13966740" from the example above.
What am I doing wrong here?
You can't concatenate strings like that in mongoDB aggregation, you'll need to concatenate strings using the concat operator, so the function "createImageURL" should look something like this,
module.exports.createImageURL = function ImageURL(){
return { $concat: [ "https://myhostingservice.com/", "$video_id", "/preview_image" ] };
};
I know that it is a bad practice to use skip in order to implement pagination, because when your data gets large skip starts to consume a lot of memory. One way to overcome this trouble is to use natural order by _id field:
//Page 1
db.users.find().limit(pageSize);
//Find the id of the last document in this page
last_id = ...
//Page 2
users = db.users.find({'_id'> last_id}). limit(10);
The problem is - I'm new to mongo and do not know what is the best way to get this very last_id
The concept you are talking about can be called "forward paging". A good reason for that is unlike using .skip() and .limit() modifiers this cannot be used to "go back" to a previous page or indeed "skip" to a specific page. At least not with a great deal of effort to store "seen" or "discovered" pages, so if that type of "links to page" paging is what you want, then you are best off sticking with the .skip() and .limit() approach, despite the performance drawbacks.
If it is a viable option to you to only "move forward", then here is the basic concept:
db.junk.find().limit(3)
{ "_id" : ObjectId("54c03f0c2f63310180151877"), "a" : 1, "b" : 1 }
{ "_id" : ObjectId("54c03f0c2f63310180151878"), "a" : 4, "b" : 4 }
{ "_id" : ObjectId("54c03f0c2f63310180151879"), "a" : 10, "b" : 10 }
Of course that's your first page with a limit of 3 items. Consider that now with code iterating the cursor:
var lastSeen = null;
var cursor = db.junk.find().limit(3);
while (cursor.hasNext()) {
var doc = cursor.next();
printjson(doc);
if (!cursor.hasNext())
lastSeen = doc._id;
}
So that iterates the cursor and does something, and when it is true that the last item in the cursor is reached you store the lastSeen value to the present _id:
ObjectId("54c03f0c2f63310180151879")
In your subsequent iterations you just feed that _id value which you keep ( in session or whatever ) to the query:
var cursor = db.junk.find({ "_id": { "$gt": lastSeen } }).limit(3);
while (cursor.hasNext()) {
var doc = cursor.next();
printjson(doc);
if (!cursor.hasNext())
lastSeen = doc._id;
}
{ "_id" : ObjectId("54c03f0c2f6331018015187a"), "a" : 1, "b" : 1 }
{ "_id" : ObjectId("54c03f0c2f6331018015187b"), "a" : 6, "b" : 6 }
{ "_id" : ObjectId("54c03f0c2f6331018015187c"), "a" : 7, "b" : 7 }
And the process repeats over and over until no more results can be obtained.
That's the basic process for a natural order such as _id. For something else it gets a bit more complex. Consider the following:
{ "_id": 4, "rank": 3 }
{ "_id": 8, "rank": 3 }
{ "_id": 1, "rank": 3 }
{ "_id": 3, "rank": 2 }
To split that into two pages sorted by rank then what you essentially need to know is what you have "already seen" and exclude those results. So looking at a first page:
var lastSeen = null;
var seenIds = [];
var cursor = db.junk.find().sort({ "rank": -1 }).limit(2);
while (cursor.hasNext()) {
var doc = cursor.next();
printjson(doc);
if ( lastSeen != null && doc.rank != lastSeen )
seenIds = [];
seenIds.push(doc._id);
if (!cursor.hasNext() || lastSeen == null)
lastSeen = doc.rank;
}
{ "_id": 4, "rank": 3 }
{ "_id": 8, "rank": 3 }
On the next iteration you want to be less or equal to the lastSeen "rank" score, but also excluding those already seen documents. You do this with the $nin operator:
var cursor = db.junk.find(
{ "_id": { "$nin": seenIds }, "rank": "$lte": lastSeen }
).sort({ "rank": -1 }).limit(2);
while (cursor.hasNext()) {
var doc = cursor.next();
printjson(doc);
if ( lastSeen != null && doc.rank != lastSeen )
seenIds = [];
seenIds.push(doc._id);
if (!cursor.hasNext() || lastSeen == null)
lastSeen = doc.rank;
}
{ "_id": 1, "rank": 3 }
{ "_id": 3, "rank": 2 }
How many "seenIds" you actually hold on to depends on how "granular" your results are where that value is likely to change. In this case you can check if the current "rank" score is not equal to the lastSeen value and discard the present seenIds content so it does not grow to much.
That's the basic concepts of "forward paging" for you to practice and learn.
The simplest way to implement pagination in MongoDB
// Pagination
const page = parseInt(req.query.page, 10) || 1;
const limit = parseInt(req.query.limit, 10) || 25;
const startIndex = (page - 1) * limit;
const endIndex = page * limit;
query = query.skip(startIndex).limit(limit);
I have some product data where some product don't have key "images.cover".
now when I try to print all data it show error
Cannot read property 'cover' of undefined.
So I try to make if images.cover key not present then just put var cover = ''; else images.cover value. I'm using nodejs and mongodb
From the error message:
Cannot read property 'cover' of undefined
you can narrow down the error source on the trouble product document to any of the three attributes:
the document doesn't have images field (hence the undefined object),
the images field may be null, and
the covers key may not be present as well.
Let's consider a minimum test case where a sample collection has documents with the above three + one with the images.cover key set:
db.product.insert([
/* 0 */
{
"_id" : 1,
"image" : {
"cover" : "test1",
"url" : "url1"
}
},
/* 1 */
{
"_id" : 2,
"image" : {
"url" : "url2"
}
},
/* 2 */
{
"_id" : 3
},
/* 3 */
{
"_id" : 4,
"image" : {
"cover" : null,
"url" : "url4"
}
}
]);
In mongo shell you can check to see if a key is present or not either by using native JavaScript methods or using mongodb's $exists operator. For the former, you could try:
var cover = "", covers = [];
db.product.find().forEach(function (doc){
var cover = "";
if ((doc.image !== undefined) && (typeof(doc.image.cover) !== "undefined") && (doc.image.cover !== undefined)){
cover = doc["image"].cover;
}
covers.push(cover);
});
print(covers); /* will print to mongo shell:
{
"0" : "test1",
"1" : "",
"2" : "",
"3" : null
}
*/
Using $exists operator with its value set to true, this searches for documents that contain the field, including documents where the field value is null. So using this route is probably not going to work in your example since you would like to assign the covers variable for unmatched documents as well:
var cover = "", covers = [];
db.product.find({ "image.cover": {$exists : true} }).forEach( function(doc) {
covers.push(doc["image"].cover);
});
print(covers); /* this will print to mongo shell:
{
"0" : "test1",
"1" : null
}
*/