Firebase query if child of child contains a value

Firebase query if child of child contains a value - javascript

The structure of the table is:
chats
--> randomId
-->--> participants
-->-->--> 0: 'name1'
-->-->--> 1: 'name2'
-->--> chatItems
etc
What I am trying to do is query the chats table to find all the chats that hold a participant by a passed in username string.
Here is what I have so far:
subscribeChats(username: string) {
return this.af.database.list('chats', {
query: {
orderByChild: 'participants',
equalTo: username, // How to check if participants contain username
}
});
}

Your current data structure is great to look up the participants of a specific chat. It is however not a very good structure for looking up the inverse: the chats that a user participates in.
A few problems here:
you're storing a set as an array
you can only index on fixed paths
Set vs array
A chat can have multiple participants, so you modelled this as an array. But this actually is not the ideal data structure. Likely each participant can only be in the chat once. But by using an array, I could have:
participants: ["puf", "puf"]
That is clearly not what you have in mind, but the data structure allows it. You can try to secure this in code and security rules, but it would be easier if you start with a data structure that implicitly matches your model better.
My rule of thumb: if you find yourself writing array.contains(), you should be using a set.
A set is a structure where each child can be present at most once, so it naturally protects against duplicates. In Firebase you'd model a set as:
participants: {
"puf": true
}
The true here is really just a dummy value: the important thing is that we've moved the name to the key. Now if I'd try to join this chat again, it would be a noop:
participants: {
"puf": true
}
And when you'd join:
participants: {
"john": true,
"puf": true
}
This is the most direct representation of your requirement: a collection that can only contain each participant once.
You can only index known properties
With the above structure, you could query for chats that you are in with:
ref.child("chats").orderByChild("participants/john").equalTo(true)
The problem is that this requires you to define an index on `participants/john":
{
"rules": {
"chats": {
"$chatid": {
"participants": {
".indexOn": ["john", "puf"]
}
}
}
}
}
This will work and perform great. But now each time someone new joins the chat app, you'll need to add another index. That's clearly not a scaleable model. We'll need to change our data structure to allow the query you want.
Invert the index - pull categories up, flattening the tree
Second rule of thumb: model your data to reflect what you show in your app.
Since you are looking to show a list of chat rooms for a user, store the chat rooms for each user:
userChatrooms: {
john: {
chatRoom1: true,
chatRoom2: true
},
puf: {
chatRoom1: true,
chatRoom3: true
}
}
Now you can simply determine your list of chat rooms with:
ref.child("userChatrooms").child("john")
And then loop over the keys to get each room.
You'll like have two relevant lists in your app:
the list of chat rooms for a specific user
the list of participants in a specific chat room
In that case you'll also have both lists in the database.
chatroomUsers
chatroom1
user1: true
user2: true
chatroom2
user1: true
user3: true
userChatrooms
user1:
chatroom1: true
chatroom2: true
user2:
chatroom1: true
user2:
chatroom2: true
I've pulled both lists to the top-level of the tree, since Firebase recommends against nesting data.
Having both lists is completely normal in NoSQL solutions. In the example above we'd refer to userChatrooms as the inverted index of chatroomsUsers.
Cloud Firestore
This is one of the cases where Cloud Firestore has better support for this type of query. Its array-contains operator allows filter documents that have a certain value in an array, while arrayRemove allows you to treat an array as a set. For more on this, see Better Arrays in Cloud Firestore.

Related

Database modelling (mongoDB)

I am trying to model a database for a fitness app. Currently the 4 main entities are as follows:
Exercise
User
Workout
UserWorkout
id
id
id
id
name
email
name
userId (fk)
body_part
name
description
workoutId (fk)
category
password
level
date
age
exerciseIds (fk)
time_taken
The app will have default workouts as well as default exercises.
I would like the user to be able to add their own custom workouts/exercises that only they can see (in addition to the default ones) but I'm not sure on how to best structure the data?

Kris, MongoDB is a schemaless database, what makes it really flexible when it comes down to data modelling. There are different ways of achieving what you described, the one I would recommend would be adding nested documents to the user document if they belong to it. You would have something like this:
User {
firstName: ...,
lastName: ...,
age: ...,
weight: ...,
exercises: [
// User's exercise objects
],
workout: [
// User's workout objects
],
}
This way you can easily have access to information related to the user and avoid using expensive operations like $lookup or querying the database multiple times.
To handle the default exercises/workouts you can have a property in the respective objects like isDefault: true.

Query firebase realtime database where child has property

I'm trying to query my Firebase Realtime Database to find all games a user belongs to.
I have a list of games, each game has a property of players. Each child of players has a key of $uid, and within that {key: $uid, name: "joe"}
Is it possible to get all games this way? Or do I need to start keeping another index of players_games/$uid/$game?
I've tried firebase.database().ref('games').orderByChild('players').equalTo(token.uid), but this yields null
It looks like database.ref('games').orderByChild('players/${token.uid}') works, but then I'd need to give .read access to all of games, or do this server-side.

Your current data structure makes it easy to find all the users for a specific game. It does not however make it easy to find all the games for a specific user. To allow that, you'll want to add an addition data structure that inverts the information.
So that'd look something like this:
player_games: {
"XDYNyN8il6TDsM4LuttwDzNuytj1": {
"-M5vf...U5zK": true
},
"NxH14...mxY2": {
"-M5vf...U5zK": true
}
}
Also see:
Firebase query if child of child contains a value
Firebase Query Double Nested
I recommend you also study the Firebase documentation on structuring your database, specifically the section on avoiding nested data. By mixing entity types as you currently do, you'll likely run into problems with security, and scalability.
The most idiomatic way to model your many-to-many relationship in the Firebase database is with four top-level lists:
players: {
$playerId: { ... }
}
games: {
$gameId: { ... }
}
player_games: {
$playerId: {
$gameId: true
}
}
game_players: {
$gameId: {
$playerId: true
}
}
Also see:
Many to Many relationship in Firebase

Best way to query/retrieve firebase data based on user key? [duplicate]

The structure of the table is:
chats
--> randomId
-->--> participants
-->-->--> 0: 'name1'
-->-->--> 1: 'name2'
-->--> chatItems
etc
What I am trying to do is query the chats table to find all the chats that hold a participant by a passed in username string.
Here is what I have so far:
subscribeChats(username: string) {
return this.af.database.list('chats', {
query: {
orderByChild: 'participants',
equalTo: username, // How to check if participants contain username
}
});
}

grabbing all of one value type from a collection

I'm working on a Discord.js bot trying to add roles to mentioned users in a command. it stores all of the mention data for the message in a collection msg.mentions.users and looks something like this.
'189920214777856000' => User {
id: '189920214777856000',
username: 'Warburp',
discriminator: '2542',
avatar: 'e83b4777a8abfd7f4cfc0f04761520b4',
bot: false,
status: 'online',
game: null } }
What Id would like to do is collect all of the id's that were mentioned into an array so I can use a for loop too add them all to a role. Distinct is not recognized when I try to use it and find required I add a value and only finds exactly what I specify.

Collection.keyArray() is possibly what you're looking for. From what I understand msg.mentions.users is a Collection object mapping IDs to User objects. So something like this will give you an array of the user IDs:
msg.mentions.users.keyArray()

Foreign key conditions in sailsjs Waterline ORM

I have defined two models like below, what i need to do is to retrieve the unique neighborhoods that belong to active partners (partner.status=1), i can retrieve the grouped neighborhoods like this
Locations.find({groupBy: [ 'neighborhood' ],sum['id']}, function(err,locations){});
and then match against a retrieved list of active Partners or backwards (ie first getting the active partners with the locations for each partner and pushing them to an array after verifying they are not already in there) or just by a custom sql query (which i am trying to stay away from)
but... i want to know if there is some kind of way to do it with the ORM as i have seen model.find().populate('model') doesn't accept parameters beyond the desired model not the where in the find method accept foreign keys conditions.
Partner:{
attributes:{
businessName:{
type:'string'
},
status:{
type:'INT'
}
locations:{
model:'Locations'
via:'partner_id'
}
}
}
Locations:{
attributes:{
partner_id:{
model:'Partners',
type:'INT'
},
neighborhood:{
type:'STRING'
}
}
}
Thanks in advance!

Is this what you looking for?
Locations.find({where: {value1: key1}})
.populate('partners', {where: {value2: key2}})
.exec(function(err, locations){
// Now you've got what you need
});
P/S: Please checkout SailsJS v0.10.x documentation on GitHub. Personally I use this: https://github.com/balderdashy/sails-docs/tree/0.10
The documents are not up-to-date though :-)

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