I'm trying to delete multiple documents that satisfy a query. However I need the data of those documents for storing them in a separate collection for undo functionality. The only way I got this to work is with multiple queries:
Data.find(query).exec(function(err, data)
{
Data.remove(query).exec(function(err2)
{
ActionCtrl.saveRemove(data);
});
});
Is there a better way? In this post: How do I remove documents using Node.js Mongoose? it was suggested to use find().remove().exec():
Data.find(query).remove().exec(function(err, data)
{
ActionCtrl.saveRemove(data);
});
However data is usually 1, don't ask me why. Can I do this without infinitely nesting my queries? Thanks!
As you have noted, using the following will not return the document:
Data.find(query).remove().exec(function(err, data) {
// data will equal the number of docs removed, not the document itself
}
As such, you can't save the document in ActionCtrl using this approach.
You can achieve the same result using your original approach, or use some form of iteration. A control flow library like async might come in handy to handle the async calls. It won't reduce your code, but will reduce the queries. See example:
Data.find(query, function(err, data) {
async.each(data, function(dataItem, callback) {
dataItem.remove(function(err, result) {
ActionCtrl.saveRemove(result, callback);
});
});
});
This answer assumes that the ActionCtrl.saveRemove() implementation can take an individual doc as a parameter, and can execute the callback from the async.each loop. async.each requires a callback to be run without arguments at the end of each iteration, so you would ideally run this at the end of .saveRemove()
Note that the remove method on an individual document will actually return the document that has been removed.
Related
I'm trying to build an application, using MongoDB and Node.JS. I have 3 models: User, Ride, Participating.
Participating contains a userID and a rideID. It is almost as with a SQL logic: Participating links the two others models.
I'd like to, using a userID, return every Ride thanks to Participating Model
I tried to use a forEach, as the first request returns an array.
router.get('/getAllRide/:userID',function(req,res){
let userID = req.params.userID
let return = []
Participating.find({_idUser: userID })
.then(participating => {
participating.forEach(element => {
Ride.find({_id: element._id})
.exec()
.then(ride => {
retour.push(ride)})
});
res.status(200).json(return)
});
At the end of this code, the array return is empty, while it is supposed to contain every Ride whose _id is in an entity Participating.
OK, there are a couple of issues here:
return is a keyword. You probably shouldn't be using it as a variable name.
Database calls are asynchronous. forEach loops are synchronous. This means that you're immediately going to be returning retour (which looks undefined).
Mongoose has tools to populate nested relationships -- it's best not to do it in application code. Even if you are doing this in application code, it's likely best not to iterate over your results & do new finds -- instead, it's better to construct a single find query that returns all of the new documents you need.
If you did want to do this in application code, you'd want to either use async/await or Promise.all:
const toReturn = [];
const findPromises = participating.map(element => {
return Ride.find({_id: element._id})
.exec()
.then(result => toReturn.push(result)
});
return Promise.all(findPromises).then(() => res.status(200).json(toReturn));
(note: rather than using Promise.all, if you're using Bluebird you could instead use Promise.map.
I'm new to Nodejs and mongoDB and I'm trying to get an aggregate function running that will select a random document from the database and return it. I've looked all over on the internet to figure out what I'm doing wrong and from what I can see my code looks like it should. For some reason however, when I try printing the result to console, it gives me an aggregation cursor object and I can't find the document I want anywhere within it. Here is my code for the aggregate function.
//get a random question
route.get('/question/random', function (req, res) {
database.collection('questions').aggregate(
[ { $sample: { size: 1} } ],
function(err, result) {
console.log(result);
})
})
It's because aggregation method returns AggregationCursor that won't return any documents unless you iterate through it.
For a simple iteration, you can do:
database.collection('questions').aggregate([{$sample: {size: 1}}]).forEach(console.log);
The forEach() method on the cursor will iterate it, and in this example will print it to the console.
I am trying to generate a response that returns the same collection sorted by 3 different columns. Here's the code I currently have:
var findRoute = router.route("/find")
findRoute.get(function(req, res) {
Box.find(function(err, boxes) {
res.json(boxes)
}).sort("-itemCount");
});
As you can see, we're making a single get request, querying for the Boxes, and then sorting them by itemCount at the end. This does not work for me because the request only returns a single JSON collection that is sorted by itemCount.
What can I do if I want to return two more collections sorted by, say, name and size properties -- all in the same request?
Crete an object to encapsulate the information and chain your find queries, like:
var findRoute = router.route("/find");
var json = {};
findRoute.get(function(req, res) {
Box.find(function(err, boxes) {
json.boxes = boxes;
Collection2.find(function (error, coll2) {
json.coll2 = coll2;
Collection3.find(function (error, coll3) {
json.coll3 = coll3;
res.json(json);
}).sort("-size");
}).sort("-name");
}).sort("-itemCount");
});
Just make sure to do the appropriate error checking.
This is kind of uggly and makes your code kind of difficult to read. Try to adapt this logic using modules like async or even promises (Q and bluebird are good examples).
If I understand well, you want something like that : return Several collections with mongodb
Tell me if that helps.
Bye.
Have you tried ?
Box.find().sort("-itemCount").exec(function(err, boxes) {
res.json(boxes)
});
Also for sorting your results based on 2 or more fields you can use :
.sort({name: 1, size: -1})
Let me know if that helps.
var Poll = mongoose.model('Poll', {
title: String,
votes: {
type: Array,
'default' : []
}
});
I have the above schema for my simple poll, and I am uncertain of the best method to change the value of the elements in my votes array.
app.put('/api/polls/:poll_id', function(req, res){
Poll.findById(req.params.poll_id, function(err, poll){
// I see the official website of mongodb use something like
// db.collection.update()
// but that doesn't apply here right? I have direct access to the "poll" object here.
Can I do something like
poll.votes[1] = poll.votes[1] + 1;
poll.save() ?
Helps much appreciated.
});
});
You can to the code as you have above, but of course this involves "retrieving" the document from the server, then making the modification and saving it back.
If you have a lot of concurrent operations doing this, then your results are not going to be consistent, as there is a high potential for "overwriting" the work of another operation that is trying to modify the same content. So your increments can go out of "sync" here.
A better approach is to use the standard .update() type of operations. These will make a single request to the server and modify the document. Even returning the modified document as would be the case with .findByIdAndUpdate():
Poll.findByIdAndUpdate(req.params.poll_id,
{ "$inc": { "votes.1": 1 } },
function(err,doc) {
}
);
So the $inc update operator does the work of modifying the array at the specified position using "dot notation". The operation is atomic, so no other operation can modify at the same time and if there was something issued just before then the result would be correctly incremented by that operation and then also by this one, returning the correct data in the result document.
I have looked a long time and not found an answer. The Node.JS MongoDB driver docs say you can do bulk inserts using insert(docs) which is good and works well.
I now have a collection with over 4,000,000 items, and I need to add a new field to all of them. Usually mongodb can only write 1 transaction per 100ms, which means I would be waiting for days to update all those items. How can I do a "bulk save/update" to update them all at once? update() and save() seem to only work on a single object.
psuedo-code:
var stuffToSave = [];
db.collection('blah').find({}, function(err, stuff) {
stuff.toArray().forEach(function(item)) {
item.newField = someComplexCalculationInvolvingALookup();
stuffToSave.push(item);
}
}
db.saveButNotSuperSlow(stuffToSave);
Sure, I'll need to put some limit on doing something like 10,000 at once to not try do all 4 million at once, but i think you get the point.
MongoDB allows you to update many documents that match a specific query using a single db.collection.update(query, update, options) call, see the documentation. For example,
db.blah.update(
{ },
{
$set: { newField: someComplexValue }
},
{
multi: true
}
)
The multi option allows the command to update all documents that match the query criteria. Note that the exact same thing applies when using the Node.JS driver, see that documentation.
If you're performing many different updates on a collection, you can wrap them all in a Bulk() builder to avoid some of the overhead of sending multiple updates to the database.