I have two collection on stores user data and another stores all invitations.
In invitation collection I only store two ids one is fromID and another is toID
I am able to get all the document array from invitations collection, but how to get the user detail from user collection.
Thanks
MongoDB isn't a relational database and isn't the best choice to store such data. That being said, you can use the $lookup function as part of an aggregate query. See the docs, here.
You can use populate to get user detail. that is assuming in your mongoose model you made the toID and fromID of type mongoose model and you set the correct ref. check the docs. http://mongoosejs.com/docs/populate.html
Related
I am trying to query my database to get all the users where the document id is equal to the users id. I know that I can add that id as a field into the document, but I'd like to optimize the memory I take up, so I'd prefer accessing the document id directly through. Something like
.whereField(DOCUMENT_ID, isEqualTo, User.id)
DOCUMENT_ID is not a valid field so far as I know, and I don't know the equivalent. I have read around that other languages modules have a workaround like
.whereField(Firebase.firestore.FieldValues.documentId(), isEqualTo, User.id)
but I've heard hide nor hair of that in swiftUI. Any ideas?
To filter on the document ID in a query, you can use FieldPath.documentID() in Swift too: https://firebase.google.com/docs/reference/swift/firebasefirestore/api/reference/Classes/FieldPath#/c:objc(cs)FIRFieldPath(cm)documentID. But if you do this in a single document, that'd be the same as just doing document(User.id).
First of all, this is not a regular question. It's little complicated.
App summary
Recipes app where users can search recipes by selected ingredients (collection ingredients exists in firestore db). I want to store for every ingredient statistics how much did users search with that selected ingredient, so I can show them later at the top ingredients which they used mostly for searching recipes.
This is how my collection looks like:
http://prntscr.com/nlz062
And now I would like to order recipes by statistics that created logged in user.
first = firebaseHelper
.getDb()
.collection(Constants.INGREDIENTS_COLLECTION)
.orderBy("statistics." + firebaseHelper.getCurrentUser().getUid() + ".count")
.limit(25);
If logged in user hasn't yet searched recipes with ingredients, then it should order normally. Anyway the query above is not working. Is it possible this use case to be done with Firestore.
Note: Statistics may exists or may not for logged in user, it all depends on his search.
You can't query and documents by fields that don't immediately exist within the document. Or, in other words, you can't use fields documents within subcollections that are not in the named collection being queried.
As of today (using the latest Firestore client libraries), you could instead perform a collection group query to query all of the subcollections called "statistics" for their count field. However, that will still only get you the statictics documents. You would have to iterate those documents, parse the ingredient document ID out of its reference, and individually get() each one of those documents in order to display a UI.
The collection group query would look something like this in JavaScript:
firestore
.collectionGroup("statistics")
.where(FieldPath.documentId())
.orderBy("count")
.limit(25)
You should be able to iterate those results and get the related documents with no problem.
use <databasename> will set a variable db to be the database
specified by <databasename>, so the database can be referred to
the variable db.
I wonder if a collection or document can also be
referred to by a variable, and if yes, how?
Every object in a MongoDB server has an identifier _id. If I am correct, a database, a collection and a document are objects.
How are the identifier of an object used in practice?
Both a database and a collection have a name. So we can refer to a
collection via its name e.g. mydb.mycollection.
Does a document also have a name?
Thanks.
A collection consists of several documents so a document as such do not have any name. _id distinguishes the documents. To fetch any particular document, you can filter it on the basis of _id or the data stored in it.
Referencing the db and then the collection in selected db will give you the required document.
Does exist anything permitting us to access a full object from a reference with Mongodb ?
For example, I have a User and a Type collection. A user has a Type, stored with a reference to the Type object.
Is it possible to access the full User object with the Type, without lazyloading it ?
Thanks for all
Yes; if you're happy making use of mongoose, then you can use its populate() function:
Populated paths are no longer set to their original _id , their value is replaced with the mongoose document returned from the database by performing a separate query before returning the results.
http://mongoosejs.com/docs/populate.html
So for your User, when performing a query to derive said user, something like this would set up the Type instance:
User.findOne({ username: 'Fred Bloggs' }).populate('type')
.exec(function (err, user) {
...
MongoDB does not do joins. It's not possible to get the information to embed the full Type object in the User document without more than one operation (I guess you have to "lazyload" it, in your terminology). The Mongoose populate() function just handles doing the extra queries and replacing the id with the document for you - it does multiple queries just like any other client doing the same operation would have to. You should think carefully about what types of queries you are doing to determine if it might be a good idea to denormalize the Type object into User documents.
I am trying to fetch the documents from a collection based on the existence of a reference to these documents in another collection.
Let's say I have two collections Users and Courses and the models look like this:
User: {_id, name}
Course: {_id, name, user_id}
Note: this just a hypothetical example and not actual use case. So let's assume that duplicates are fine in the name field of Course. Let's thin Course as CourseRegistrations.
Here, I am maintaining a reference to User in the Course with the user_id holding the _Id of User. And note that its stored as a string.
Now I want to retrieve all users who are registered to a particular set of courses.
I know that it can be done with two queries. That is first run a query and get the users_id field from the Course collection for the set of courses. Then query the User collection by using $in and the user ids retrieved in the previous query. But this may not be good if the number of documents are in tens of thousands or more.
Is there a better way to do this in just one query?
What you are saying is a typical sql join. But thats not possible in mongodb. As you suggested already you can do that in 2 different queries.
There is one more way to handle it. Its not exactly a solution, but the valid workaround in NonSql databases. That is to store most frequently accessed fields inside the same collection.
You can store the some of the user collection fields, inside the course collection as embedded field.
Course : {
_id : 'xx',
name: 'yy'
user:{
fname : 'r',
lname :'v',
pic: 's'
}
}
This is a good approach if the subset of fields you intend to retrieve from user collection is less. You might be wondering the redundant user data stored in course collection, but that's exactly what makes mongodb powerful. Its a one time insert but your queries will be lot faster.