I am working on photo sharing application that has a mongodb model that looks a bit like:
Location = { _id : id, address : address, name : name }
Photo = {
_id: id,
_upvotes : [{ ref to User }],
_location : {ref to Location},
url: url,
selected : boolean
}
A quick overview of the code that I want to modify (nodejs/expressjs/mongoose):
Photo.find({})
.populate('_location')
.stream({ objectMode : true })
.pipe(res);//res being response stream in express.js
Is there a way to query on Photo model in such a way that:
If there is no Photo.selected in a Location
Then find the photo with maximum votes, by counting the length of upvotes
I did a deep research using MongoDBs mapReduce implementation, agregation framework, and $where operator, but did not find my way out.
If there is any other question, or reference that may lead to an answer, or a specific approach to follow, please let me know.
Related
I am finding data from an array. that is a course and I want to find out an article by using the title, which is stored into the Course's Articles. I am going step by step...
(1) I want fine the course by the name,
(2) after of it, I want to find an article into course's article by using the title of an article
(3) and render the article and course to the web page
here is code
const course = req.params.course
const article_title = req.query.article
Course.findOne({name: course , article:article_title}).then(function(data){
console.log(data)
res.render('article',{data :data})
}).catch((err)=>{console.log(err)});
here is DB
_id:61c057cfd70f2fb178d4e996
name:"Soft "
discription:"House"
article:Array
0:Object
title:"Where does it come from?"
content:"<p>Title is very important for an article to explain content | article..."
_id:61c05d4a3905f61f72a8e61b
1 :Object
2:Object
To search you can use:
Couse.findOne({name: course, 'article.title': article_title})
So you will get the document with the articles you need.
Using projection and $elemMatch, you can filter the article array itself so that only the subdocument you want is there:
Couse.findOne({name: course, 'article.title': article_title}, {
article: {
$elemMatch: {
title: article_title
}
}
})
You can try it in MongoPlayground
https://mongoplayground.net/p/SVXNGE6tuW7
I'm using Mongoose in Node.js, and I am wondering if it is possible to refer to the currently selected document using "this" or a similar mechanism. Here is the use case I'm looking for :
Mongoose Schema :
const mySchema = mongoose.Schema({
position: Number,
date: Number,
lastEventDate: Number
});
Let's say that, at some point in time, an event occurs.
For a document selected through its position, I want to update "lastEventDate" to the document's date.
Here is my dream code :
myModel.findOneAndUpdate(
{position: myPosition},
{$set: {
'lastEventDate': THISDOCUMENT.date
}}
);
Note : I'm using $set here because the actual code updates subdocuments...
Is there a built-in "THISDOCUMENT" reference such as the one I'm dreaming of, to do it all in a single query ?
Or do I have to first query the value before updating the document (two queries).
Couldn't find anything on the web, and I'm quite the newbie when it comes to using "this".
Thanks for any kind of help !
[EDIT :] Precisions about the objective :
I am in a situation where I only have the position "myPosition" to identify the correct document, and I want to set "lastEventDate" to the same value as "date" for that document.
My question is about efficiency : is it possible to perform the update in a single upload query ? Or do I have to first download the "date" value before uploading it back to the "lastEventDate" key ?
Gathering all the information provided, I will venture on a possible answer!
You could try something like:
Your schema JS file
const mySchema = mongoose.Schema({
position: Number,
date: Number,
lastEventDate: Number
});
mySchema.methods.doYourThing(){
this.lastEventDate=this.date; //it will set the lastEventDate
}
mongoose.model("myModel", MySchema, "mycollection")
Now, whenever you call doYourThing(), the action wanted will take place, you call it after you have a instance of the mode.
This is from my own code
const token = user.generateJwt(expirationDate); //send a token, it will be stored locally in the browser
it is inside a function that return an instance of user, and in the model User I have done a function called generateJwt like I have showed, and we have something like this:
return jwt.sign(
{
_id: this._id, //this is created automatically by Mongo
email: this.email,
name: this.name,
exp: parseInt(expiry.getTime() / 1000, 10), //Includes exp as UNIX time in seconds
level: this.level,
lastLogin: this.lastLogin,
failedLogin: this.failedLogin
},
process.env.JWT_SECRET
); // DO NOT KEEP YOUR SECRET IN THE CODE!
It returns all the information of the user!
Please, do not hesitate to add comments and feebacks, I am not sure it is what you want, but that is why I have understood your request.
Anothe option is using Virtuals, they also have access to this.
So I have an object using a dictionary to store products that a user has added to the cart in a shopping cart application. I am taking is object and attempting to insert into mongoDB with zero luck.
The piece of data I am attempting to insert looks like this:
products: '{"rJUg4uiGl":{"productPrice":"78.34","count":2},"BJ_7VOiGg":{"productPrice":"3","count":2}}' }
My process of attempting to insert it into mongoDB looks like this:
db.orders.insert("products":{"rJUg4uiGl":{"productPrice":"78.34","count":2},"BJ_7VOiGg":{"productPrice":"3","count":2}});
Currently with this approach I get the following error:
2016-12-15T18:11:43.862-0500 E QUERY [thread1] SyntaxError: missing ) after argument list #(shell):1:27
Which is implying there is some sort of a formatting issue with inserting it. I have moved quotation marks and parenthesis around plenty, simply to either get the above error, or a ... response from mongoDB implying that it is waiting for me to do something more to fix what exactly is causing an error.
Any chance anyone could help give some guidance in the best way to store this object in mongoDB?
My true question feels that it should have been in regards to the mongoose schema that would be used in order to store this data format. I hoped that getting how to initially insert it into mongodb was going to be enough but the way the data is being saved has me a bit confused. I know this is a bit of an awful question but could I get any assistance with setting up my schema for this as well?
"products" : {
"rJUg4uiGl" : {
"productPrice" : "78.34",
"count" : 2
},
"BJ_7VOiGg" : {
"productPrice" : "3",
"count" : 2
}
}
This is what the data looks like when it is stored in mongo. I think what is confusing me on how to set up is the "rJUg4uiGl" portion of the data. I am un-sure of how exactly that is suppose to look in mongoose schema. Here are a few of my rather poor attempts:
products: {
productId: {
productPrice: Number,
count: Number
}
}
Above simply doesn't store anything in the database
products: {
productId: [{
productPrice: Number,
count: Number
}]
}
Above gives:
"products" : {
"productId" : [ ]
}
Again, I know that this is quite specific but any help at all would be extremely appreciated.
Need to wrap your insert data in {}
db.orders.insert({"products":{"rJUg4uiGl":{"productPrice":"78.34","count":2},"BJ_7VOiGg":{"productPrice":"3","count":2}}});
I am modelling two types of events (events and subevents) in a MongoDB like this:
var EventSchema = mongoose.Schema({
'name' : String,
'subEvent' : [ SubeventSchema ]
});
var SubeventSchema = mongoose.Schema({
'name' : String
});
Now when I query a subevent I want to be able to also retrieve data about its corresponding superevent, so that some example data retrieved using Mongoose population feature could look like this:
EventModel.findOne({
name : 'Festival'
})
.populate('subEvent')
.execute(function (err, evt) { return evt; });
{
name : 'Festival',
subEvent: [
{ name : 'First Concert' },
{ name : 'Second Concert' }
]
}
EventModel.findOne({
'subEvent.name' : 'FirstConcert'
}, {
'subEvent.$' : 1
})
.populate('superEvent') // This will not work, this is the actual problem of my question
.execute(function (err, subevt) { return subevt; });
{
name: 'First Concert',
superEvent: {
name: 'Festival'
}
}
A solution I can think of is not to embed but to reference like this:
var EventSchema = mongoose.Schema({
'name' : String,
'subEvent' : [ {
'type' : mongoose.Schema.Types.ObjectId,
'ref' : 'SubeventSchema'
} ]
});
var SubeventSchema = mongoose.Schema({
'name' : String,
'superEvent' : {
'type' : mongoose.Schema.Types.ObjectId,
'ref' : 'EventSchema'
}
});
I am looking for a solution based on the first example using embedded subevents, though. Can this be achieved and in case yes, how?
I think your mental model of document embedding isn't correct. The major misunderstanding (and this is very common) is that you "query a subevent" (query an embedded document). According to your current Event schema, a Subevent is just a document embedded in an Event document. The embedded SubEvent is not a top-level document; it's not a member of any collection in MongoDB. Therefore, you don't query for it. You query for Events (which are the actual collection-level documents in your schema) whose subEvents have certain properties. E.g. one way people translate the query
db.events.find({ "subEvent" : { "name" : "First Concert" } })
into plain English is as "find all the subevents with the name "First Concert". This is wrong. The right translation is "find all events that have at least one subevent whose name is "First Concert" (the "at least one" part depends on knowledge that subEvent is an array).
Coming back to the specific question, you can hopefully see now that trying to do a populate of a "superevent" on a subevent makes no sense. Your queries return events. The optimal schema, be it subevents embedded in events, one- or two-way references between events and subevents documents in separate collections, or events denormalized into the constituent subevent documents, cannot be determined from the information in the question because the use case is not specified.
Perhaps this is a situation where you need to modify your thinking rather than the schema itself. Mongoose .populate() supports the basic ideas of MongoDB "projection", or more commonly referred to as "field selection". So rather than try to model around this, just select the fields you want to populate.
So your second schema form is perfectly valid, just change how you populate:
EventModel.find({}).populate("subEvent", "name").execute(function(err,docs) {
// "subevent" array items only contain "name" now
});
This is actually covered in the Mongoose documentation under the "populate" section.
Help me with understanding mongodb, please.
have three collections: threads, messages and users.
thread
{ "title" : "1212", "message" : "12121", "user_id" : "50ffdfa42437e00223000001", "date" : ISODate("2013-04-11T19:48:36.878Z"), "_id" : ObjectId("51671394e5b854b042000003") }
message
{ "message" : "text", "image" : null, "thread_id" : "51671394e5b854b042000003", "user_id" : "516d08a7772d141766000001", "date" : ISODate("2013-04-17T15:58:07.021Z"), "_id" : ObjectId("516ec68fb91b762476000001") }
user
{ "user" : "admin", "date" : ISODate("2013-04-16T08:15:35.497Z"), "status" : 1, "_id" : ObjectId("516d08a7772d141766000001") }
How can I display all messages for current thread and get user name (for comment) from users collection?
this code get only messages without user name
exports.getMessages = function(id, skip, callback) {
var skip = parseInt(skip);
messages.find({thread_id: id}).sort({date: 1}).skip(skip).limit(20).toArray(
function(e, res) {
if (e) {
callback(e)}
else callback(null, res)
});
};
Node.js and mongo native
Generally, Mongo uses embedded documents or references to maintain relationships. Here is a link from the mongo docs worth reading.
What you are currently doing is storing a manual reference to the user collection within your message collection. Mongo manual references require additional queries in order to get that referenced data. In this case, using a reference based relationship will work, but it would force the N+1 query problem. Meaning you will have to make an addition query for every message you wish to display plus the original query for messages. References are explained in further detail here. One solution would be to incorporate DBRefs, which would require language specific driver support.
Another alternative would be use embedded documents. In this case you would store the related user object embedded within the messages object. Here is another link to the mongo docs with a great example. In this case, you would make a single query, which will return all of the messages, with each related user object embedded inside. Although embedded documents encourage duplicate data, in many cases they provide performance benefits. All of this information is explained in the mongo docs and can be read in detail to further understand the data modeling of mongo.
Additionally, the mongoose library is pretty awesome and has a populate function which is helpful for references.