Is there any way to on Firebae to filter data in an array?
I have this model on my Firebase:
-KABIGeWnBMUKjLTcvp8
deviceToken:"7DE60240CB4B712F05A009F32358610C1327917E7E68409..."
favorites
0:"Masha"
1:"moksha"
name:"juan"
And the problem is that I can't find any method to get all "users" that contain a certain value on the "favorites" array field.
Nope, that's not an option See firebase equivalent to sql where in ().
Instead: invert your data structure to make this query possible:
items_by_favorites
"Masha"
"-KABIGeWnBMUKjLTcvp8"
"moksha"
"-KABIGeWnBMUKjLTcvp8"
Now you can look up the item keys for Masha with a simple read: ref.child('items_by_favorites/Masha') and then load each item:
ref.child('items_by_favorites/Masha').on('value', function(snapshot) {
snapshot.forEach(function(childSnapshot) {
var key = childSnapshot.key();
ref.child('items').child(key).once('value', function(itemSnapshot) {
console.log(itemSnapshot.val());
});
});
})
First of all your question is answered deep in the guide for retrieving data, which is where I got this answer. It's under complex queries, then range queries, should you want more info.
var ref = new Firebase("https://dinosaur-facts.firebaseio.com/dinosaurs");
ref.orderByChild("height").equalTo(25).on("child_added", function(snapshot) {
console.log(snapshot.key());
});
The basic idea is that you need to first order the reference by a common child value, and then call .equalTo() to end up with a query that yields what you want.
Also you can call order by child like
ref.orderByChild("height/sublevel")
To drill deeper in the tree.
FirebaseFirestore.instance.collection('your collection name').where('favorite', arrayContains: 'Masha').snapshot();
Related
I have the following Firestore database structure in my Ionic 5 app.
Book(collection)
{bookID}(document with book fields)
Like (sub-collection)
{userID} (document name as user ID with fields)
Book collection has documentes and each document has a Like sub-collection. The document names of Like collection are user IDs who liked the book.
I am trying to do a query to get the latest books and at the same time trying to get the document from Like sub-collection to check if I have liked it.
async getBook(coll) {
snap = await this.afs.collection('Book').ref
.orderBy('createdDate', "desc")
.limit(10).get();
snap.docs.map(x => {
const data = x.data();
coll.push({
key: x.id,
data: data.data(),
like: this.getMyReaction(x.id)
});
}
async getMyReaction(key) {
const res = await this.afs.doc('Book/myUserID').ref.get();
if(res.exists) {
return res.data();
} else {
return 'notFound';
}
}
What I am doing here is calling the method getMyReaction() with each book ID and storing the promise in the like field. Later, I am reading the like value with async pipe in the HTML. This code is working perfectly but there is a little delay to get the like value as the promise is taking time to get resolved. Is there a solution to get sub-collection value at the same time I am getting the collection value?
Is there a solution to get sub-collection value at the same time I am getting the collection value?
Not without restructuring your data. Firestore queries can only consider documents in a single collection. The only exception to that is collection group queries, which lets you consider documents among all collections with the exact same name. What you're doing right now to "join" these two collections is probably about as effective as you'll get.
The only way you can turn this into a single query is by having another collection with the data pre-merged from the other two collections. This is actually kind of common on nosql databases, and is referred to as denormalization. But it's entirely up to you to decide if that's right for your use case.
I'm working in a MongoDB query with Nodejs and I have a problem that I can't resolve.
Let us supposed we have a lot of documents in Mongo and each document have a tags array
tags: [tag1, tag2, tag3]
Front-end are going to send the parameters and we want to make a query with those... How can I find every document inside Mongo with those tags. The tags can be differents, not all documents have the same tags but I want to pull each document that have almost one of those tags. I don't know if I make myself clear with this but I hope you'll help me.
PD: If the query works, we have more than 13 that I can apply so it needs to be something like dynamically query o something.
Regards
This is where the mongodb's aggregate function comes in play
lets say there is a database called books and we want to get books that contain lets say ['fantasy', 'sci-fi'] in its genres
db.book.aggregate([{
$match:{
genres:{
$in:['fantasy', 'sci-fi']
}
}
}])
this will get the result you want, finding all the books that contain either fantasy, or scifi
db.book.aggregate([{
$match:{
genres:{
$all:['fantasy', 'sci-fi']
}
}
}])
This will get all the books that have genres with both fantasy and sf
db.book.aggregate([{
$match:{
genres:{
$nin:['fantasy', 'sci-fi']
}
}
}])
This will fetch all the books that don't have these values
generate an $or condition in your code according to the parameters:
let or_array = [];
params.forEach(params, (tag_param) => {
or_array.push({tags: tag_param})
});
let or_cond = {$or: or_array};
now we just need a simple find query to retrieve the documents:
let results = model.find(or_cond);
results should contain the wanted documents.
** note that $or requires a none empty array so you should validate at least one parameter is received from the client side.
In Mongoose, I can use a query populate to populate additional fields after a query. I can also populate multiple paths, such as
Person.find({})
.populate('books movie', 'title pages director')
.exec()
However, this would generate a lookup on book gathering the fields for title, pages and director - and also a lookup on movie gathering the fields for title, pages and director as well. What I want is to get title and pages from books only, and director from movie. I could do something like this:
Person.find({})
.populate('books', 'title pages')
.populate('movie', 'director')
.exec()
which gives me the expected result and queries.
But is there any way to have the behavior of the second snippet using a similar "single line" syntax like the first snippet? The reason for that, is that I want to programmatically determine the arguments for the populate function and feed it in. I cannot do that for multiple populate calls.
After looking into the sourcecode of mongoose, I solved this with:
var populateQuery = [{path:'books', select:'title pages'}, {path:'movie', select:'director'}];
Person.find({})
.populate(populateQuery)
.execPopulate()
you can also do something like below:
{path:'user',select:['key1','key2']}
You achieve that by simply passing object or array of objects to populate() method.
const query = [
{
path:'books',
select:'title pages'
},
{
path:'movie',
select:'director'
}
];
const result = await Person.find().populate(query).lean();
Consider that lean() method is optional, it just returns raw json rather than mongoose object and makes code execution a little bit faster! Don't forget to make your function (callback) async!
This is how it's done based on the Mongoose JS documentation http://mongoosejs.com/docs/populate.html
Let's say you have a BookCollection schema which contains users and books
In order to perform a query and get all the BookCollections with its related users and books you would do this
models.BookCollection
.find({})
.populate('user')
.populate('books')
.lean()
.exec(function (err, bookcollection) {
if (err) return console.error(err);
try {
mongoose.connection.close();
res.render('viewbookcollection', { content: bookcollection});
} catch (e) {
console.log("errror getting bookcollection"+e);
}
//Your Schema must include path
let createdData =Person.create(dataYouWant)
await createdData.populate([{path:'books', select:'title pages'},{path:'movie', select:'director'}])
Suppose I have 2 Schema's in Mongoose that look like this:
var movieSchema = mongoose.Schema({
name: String,
type: String
});
var moviePlaylistSchema = mongoose.Schema({
name: String,
movies: [{type: mongoose.Schema.Types.ObjectId, ref: 'Movie'}]
});
var Movie = mongoose.model('Movie', movieSchema);
var MoviePlaylist = mongoose.model('MoviePlaylist', moviePlaylistSchema);
If a query was made along the following lines:
MoviePlaylist.find({}).populate('movies').exec(function(err, res) {
if (err) console.log('err', err);
else {
console.log('res', res);
res.forEach(function(elem, index) {
console.log('elem.name', elem.name);
});
}
});
Would the order of the elements in the array be maintained? The objective here is to allow the user to maintain a playlist order of their movies. If, when the "populate" method fires, the array order of Movie object Ids is not maintained, then this will not serve my purpose. Hence thought I'd ask someone who is more knowledgeable in this area.
If this works, then I have another task which is allowing the user to change the order of movies in the playlist, which should be straight forward by allowing the movie object id index to be swapped in the array.
Thanks for your help in advance.
MongoDB will keep the order of the array, much like an array in any programming language.
You can view the BSON/JSON spec for reference which highlights that the array must contain integer values for keys, and be maintained in ascending numerical order.
Additionally, the Mongoose populate on an array works by calling Model.populate via forEach on each element of the array. This modifies the array in place, hence the order is preserved. You can see the relevant source code here.
Say I'd like to fetch only items that contains keys: "-Ju2-oZ8sJIES8_shkTv", "-Ju2-zGVMuX9tMGfySko", and "-Ju202XUwybotkDPloeo".
var items = new Firebase("https://hello-cambodia.firebaseio.com/items");
items.orderByKey().equalTo("-Ju2-gVQbXNgxMlojo-T").once('value', function(snap1){
items.orderByKey().equalTo("-Ju2-zGVMuX9tMGfySko").once('value', function(snap2){
items.orderByKey().equalTo("-Ju202XUwybotkDPloeo").once('value', function(snap3){
console.log(snap1.val());
console.log(snap2.val());
console.log(snap3.val());
})
})
});
I don't feel that this is the right way to fetch the items, especially, when I have 1000 keys over to fetch from.
If possible, I really hope for something where I can give a set of array
like
var itemKeys = ["-Ju2-gVQbXNgxMlojo-T","-Ju2-zGVMuX9tMGfySko", "-Ju202XUwybotkDPloeo"];
var items = new Firebase("https://hello-cambodia.firebaseio.com/items");
items.orderByKey().equalTo(itemKeys).once('value', function(snap){
console.log(snap.val());
});
Any suggestions would be appreciated.
Thanks
Doing this:
items.orderByKey().equalTo("-Ju2-gVQbXNgxMlojo-T")
Gives exactly the same result as:
items.child("-Ju2-gVQbXNgxMlojo-T")
But the latter is not only more readable, it will also prevent the need for scanning indexes.
But what you have to answer is why want to select these three items? Is it because they all have the same status? Because they fell into a specific date range? Because the user selected them in a list? As soon as you can identify the reason for selecting these three items, you can look to convert the selection into a query. E.g.
var recentItems = ref.orderByChild("createdTimestamp")
.startAt(Date.now() - 24*60*60*1000)
.endAt(Date.now());
recentItems.on('child_added'...
This query would give you the items of the past day, if you had a field with the timestamp.
You can use Firebase child. For example,
var currFirebaseRoom = new Firebase(yourFirebaseURL)
var userRef = currFirebaseRoom.child('users');
Now you can access this child with
userRef.on('value', function(userSnapshot) {
//your code
}
You generally should not be access things using the Firebase keys. Create a child called data and put all your values there and then you can access them through that child reference.