I'm using watch() function of mongo to listen to changes made to a replicaSet, now I know I can get the whole document (fullDocument) by passing { fullDocument: 'updateLookup' } to the watch method,
like :-
someModel.watch({ fullDocument: 'updateLookup' })
But what I really want to do is, get just one extra field which isn't changed every time a new update is made.
Let's say a field called 'user_id', currently I only get the updatedFields and the fullDocument which contains the 'user_id' along with a lot of other data which I would like to avoid.
What I have researched so far is Aggregation pipeline but couldn't figure out a way to implement it.
Can anybody help me figure out a way to this?
Thanks everyone for suggesting, as #D.SM pointed out I successfully implemented $project
Like this :-
const filter = [{"$match":{"operationType":"update"}}, {"$project":{"fullDocument.user_id": 1, "fullDocument.chats": 0, "fullDocument._id": 0, "fullDocument.first_name": 0, "fullDocument.last_name": 0 }}];
Then passed it to watch() method
Like:-
const userDBChange = userChatModel.watch(filter, { fullDocument: 'updateLookup' });
Now I'm only getting user_id inside fullDocument object when the operationType is update hence reducing the data overhead returned from mongo
Thanks again #D.SM and other's for trying to help me out ;)
Related
Checked couple of old similar questions but no luck in finding the right answers.
I have a mongo query that uses await/async to fetch results from the database, So the code looks like this :
(async () => {
//get connection object
const db = await getDatabaseConnection("admindb");
//get user data object
const configResponse = await db.collection("config").find({}).toArray();
//prints results
console.log("Successfully Fetched Configuration", configResponse);
})();
The above code works fine, just that it returns me an array of elements since I have used the .toArray() method.
Sample Result:
[
{
_id: "6028d30db7ea89f74df013d9",
tokenize: false,
configurations: { theme: {} }
}
]
Is there a NATIVE WAY (not looking forEach responses) to get result as an object since I will always have only one document returned. I have multiple queries that returns only one document, Hence accessing using the 0th index everytime did not seem the right way.
I am thinking if the findOne() will help you.
Check this out docs
await db.collection("config").findOne({});
Here are some examples
So I've got an object that looks like this
{"_id":"5fb07ab6215679200cef0eb1","user":{"_id":"5fb07437538fcd2870e21a8e","email":"example#example.com","id":"5fb07437538fcd2870e21a8e"},"question":"question?","answers":[{"_id":"5fb07ab6215679200cef0eb2","answer":"Yes","votes":0}],"voters":[],"createdAt":"2020-11-15T00:47:50.156Z","updatedAt":"2020-11-15T00:47:50.156Z","__v":0,"id":"5fb07ab6215679200cef0eb1"}
and I'm trying to increase the votes variable by this function using findOneAndUpdate
export const castVote = async (id, answersid) =>
Poll.findOneAndUpdate(
{ id, 'answers._id': answersid },
{ $inc: { 'answers.$.votes': 1 } }
);
As far as i can see calling castVote("5fb07ab6215679200cef0eb1", "5fb07ab6215679200cef0eb2") works as in not crashing the server and not giving any errors back, but the votes variable in the answers object doesn't increase so something must be wrong. Is there something obvious I'm missing here?.
got it working by simply dropping the id field which i guess i enough since they're uniquely created
I'm trying to limit the amount of elements a user can add to an array field on one of my schemas. I'm currently adding the elements to the array using Schema.findOneAndUpdate(); with the $push operator.
The first thing I tried was the solution given by another answer here on StackOverflow, namely: https://stackoverflow.com/a/29418656/6502807
This solution adds a validate function to the fields in the schema definition. By setting runValidators to true, I did get the function to run with Schema.findOneAndUpdate(). It was at that moment, however, that I stumbled upon the next problem. At the end of the Validation chapter in the Mongoose docs it says:
Also, $push, $addToSet, $pull, and $pullAll validation does not run any validation on the array itself, only individual elements of the array.
So attempting to check for array length did not work when using $pull. It simply supplied the validation function with an empty array every time, regardless of its actual contents in the database.
Next thing I tried was to use a pre hook. This was without any success as well. For some reason it did not execute the hook, even with runValidators set to true. This is how I defined said hook:
Settings.pre('update', async function (next) {
if (this.messages.length > MAX_MESSAGES) {
throw new Error('Too many messages');
} else {
next();
}
});
EDIT: The reason the function did not fire was because I was using findOneAndUpdate instead of update this is fixed and the function now runs. The solution code above, however, does not work.
The schema with the array looks like this:
const Settings = new mongoose.Schema({
// A lot more fields not relevant to this question
messages: {
type: [{
type: String
}]
}
});
Another thing worth mentioning is that these update statements are used in conjunction with other options. I need the update statement to behave like an update or insert so my complete set of options looks like this:
{
runValidators: true,
setDefaultsOnInsert: true,
upsert: true,
new: true
}
When executing queries with the pre hook set like this, the array limit can be exceeded without any validation error being thrown.
At this point I'm wondering if there is any sensible way to do a max length check like this without having to do it myself outside of mongoose's abstraction layer.
I am using Mongoose 5.2.6 running on node v9.11.1 with MongoDB 4.0.0.
Any help is much appreciated!
Well if you are using latest version from mongodb and mongoose then you can use $expr operator
const udpate = await db.collection.update(
{ $expr: { $gt: [{"$size": "$messages" }, MAX_MESSAGES] }},
{ update }
)
You should be able to do that with the pre update hook. The thing is that that hook would not by default give you the update being mage so you can verify etc. You have to take it via this.getUpdate():
Settings.pre('update', async function (next) {
var preUpdate = this.getUpdate()
// now inside of the preUpdate you would have your update being made and should have the array in there on which you can check the length
});
To give you an idea in my test schema I had to do something like this on an update with a $set:
this.getUpdate().$set.books.length // gave me 2 which was correct etc
I also had no issues running and hitting the update hook at all. It looks super simple out of the mongoose docs:
AuthorSchema.pre('update', function(next) {
console.log('UPDATE hook fired!')
console.log(this.getUpdate())
next();
});
I'm working with the mean stack I'm trying to update the following object:
{
_id : "the id",
fields to be updated....
}
This is the function that does the updating:
function updateById(_id, update, opts){
var deferred = Q.defer();
var validId = new RegExp("^[0-9a-fA-F]{24}$");
if(!validId.test(_id)){
deferred.reject({error: 'invalid id'});
} else {
collection.findOneAndUpdate({"_id": new ObjectID(_id)}, update, opts)
.then(function(result){
deferred.resolve(result);
},
function(err){
deferred.reject(err);
});
}
return deferred.promise;
}
This works with some of my objects, but doesn't work with others.
This is what is returned when it fails to update:
{
ok: 1,
value:null
}
When the function is successful in updating the object it returns this:
{
lastErrorObject: {}
ok: 1
value: {}
}
It seems like Mongo is unable to find the objects I'm trying to update when it fails. However, I can locate those objects within the Mongo shell using their _id.
Does anybody know why the driver would be behaving this way? Could my data have become corrupt?
Cheers!
I found the answer and now this question seems more ambiguous so I apologize if it was confusing.
The reason I was able to find some of the documents using ObjectID(_id) was because I had manually generated some _id fields using strings.
Now I feel like an idiot but, instead of deleting this question I decided to post the answer just in case someone is running into a similar issue. If you save an _id as a string querying the collection with the _id field changes.
querying collection with MongoDB generated _ids:
collection.findOneAndUpdate({"_id": new ObjectID(_id)}, update, opts)
querying collection with manually generated _ids:
collection.findOneAndUpdate({"_id": _id}, update, opts)
In the second example _id is a string.
Hope this helps someone!
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.