I am bit familiar with NoSQL and Firebase Realtime Database and also I know that it is not best solution to solve tasks where relational database should be more appropriate. I want to verify about structure of simple many to many relationship that I have.
I have events and users. I want to use Firebase for storing information about users participating in events, later I will need to
Get list of users for event knowing it's id and city
Get list of events for users knowing it's id and city
add or delete information about user attending to event
I would like to have first tree of events ids divided by cities.
events {
'city1' : {
event_id_1 : {'user_1', 'user_2'},
event_id_2 : {'user_3', 'user_4'}.
}
'city2' : {
event_id_3 : {'user_5', 'user_6'},
event_id_4 : {'user_7', 'user_7'}.
}
}
And second tree for users
users {
'user1' : {
'city1' : {event_id_1, event_id_2},
'city2' : {event_id_3, event_id_4},
'city3' : {event_id_3, event_id_4}
},
'user2' : {
'city1' : {event_id_1, event_id_2},
'city2' : {event_id_3, event_id_4},
'city3' : {event_id_3, event_id_4}
},
'user3' : {
'city1' : {event_id_1, event_id_2},
'city2' : {event_id_3, event_id_4},
'city3' : {event_id_3, event_id_4}
},
}
Would it be easy and fast to use and maintain?
Your structure looks pretty OK to me given the requirements listed. Most importantly: you store the data in both directions already, which is the biggest hurdle for many developers new to NoSQL data modeling.
A few notes about your data model, though most are on the level of typos:
Be sure to store the data as maps, not arrays. So event_id_1 : {'user_1': true, 'user_2': true }
If there is a many-to-many relationship between users and events, I'd usually have four top-level lists: users and events (for the primary information about each), and then userEvents and eventUsers (for connections between the two).
Adding a user to an event can be done with a single multi-location update, e.g.:
ref.update({
'/userEvents/userId1/eventId1': true,
'/eventUsers/eventId1/userId1': true
});
Unregistering them is a matter of doing the same with null as the value (which deletes the existing key):
ref.update({
'/userEvents/userId1/eventId1': null,
'/eventUsers/eventId1/userId1': null
});
Also see my answer here: Many to Many relationship in Firebase
You can do this:
List of user
Users
useruid
name:userx
email:userx#gmail.com
useruid
name:usery
email:usery#gmail.com
Events
eventid
useruid
name:userx
location: city1
eventname: party
eventid2
useruid1
name:usery
location: city2
eventname: Boring Party
Get list of users for event knowing it's id and city:
DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("Events").child(eventid);
ref.orderByChild("location").equalTo(city1);
//retrieve users using a listener
Get list of events for users knowing it's id and city:
DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("Events");
Query q=ref.orderByChild("location").equalTo(city1);
using a listener this can give you the events that are in location:city1
Related
In my main page I have a list of users and i'd like to choose and open a channel to chat with one of them.
I am thinking if use the id is the best way and control an access of a channel like USERID1-USERID2.
But of course, user 2 can open the same channel too, so I'd like to find something more easy to control.
Please, if you want to help me, give me an example in javascript using a firebase url/array.
Thank you!
A common way to handle such 1:1 chat rooms is to generate the room URL based on the user ids. As you already mention, a problem with this is that either user can initiate the chat and in both cases they should end up in the same room.
You can solve this by ordering the user ids lexicographically in the compound key. For example with user names, instead of ids:
var user1 = "Frank"; // UID of user 1
var user2 = "Eusthace"; // UID of user 2
var roomName = 'chat_'+(user1<user2 ? user1+'_'+user2 : user2+'_'+user1);
console.log(user1+', '+user2+' => '+ roomName);
user1 = "Eusthace";
user2 = "Frank";
var roomName = 'chat_'+(user1<user2 ? user1+'_'+user2 : user2+'_'+user1);
console.log(user1+', '+user2+' => '+ roomName);
<script src="https://getfirebug.com/firebug-lite-debug.js"></script>
A common follow-up questions seems to be how to show a list of chat rooms for the current user. The above code does not address that. As is common in NoSQL databases, you need to augment your data model to allow this use-case. If you want to show a list of chat rooms for the current user, you should model your data to allow that. The easiest way to do this is to add a list of chat rooms for each user to the data model:
"userChatrooms" : {
"Frank" : {
"Eusthace_Frank": true
},
"Eusthace" : {
"Eusthace_Frank": true
}
}
If you're worried about the length of the keys, you can consider using a hash codes of the combined UIDs instead of the full UIDs.
This last JSON structure above then also helps to secure access to the room, as you can write your security rules to only allow users access for whom the room is listed under their userChatrooms node:
{
"rules": {
"chatrooms": {
"$chatroomid": {
".read": "
root.child('userChatrooms').child(auth.uid).child(chatroomid).exists()
"
}
}
}
}
In a typical database schema each Channel / ChatGroup has its own node with unique $key (created by Firebase). It shouldn't matter which user opened the channel first but once the node (& corresponding $key) is created, you can just use that as channel id.
Hashing / MD5 strategy of course is other way to do it but then you also have to store that "route" info as well as $key on the same node - which is duplication IMO (unless Im missing something).
We decided on hashing users uid's, which means you can look up any existing conversation,if you know the other persons uid.
Each conversation also stores a list of the uids for their security rules, so even if you can guess the hash, you are protected.
Hashing with js-sha256 module worked for me with directions of Frank van Puffelen and Eduard.
import SHA256 from 'crypto-js/sha256'
let agentId = 312
let userId = 567
let chatHash = SHA256('agent:' + agentId + '_user:' + userId)
I am trying to access to a object into another object in my firebase database, i have a structure like this:
I want to get all the objects that have the email that i send by parameters, i am using .child to access to the childs into my object but i am not success with the query, this is my code
$ ref_db.child("/groups").child("members").orderByChild("email").equalTo(email).once("value", (snapshot)=>{
console.log(snapshot.val());
});
The snapshot.val() always is undefined.
could you help me with the query?
One efficient way to get "all the groups that have that email inside the members object" would be to denormalize you data and have another "main node" in your database where you store all "members" (i.e. their email) and the "groups" they belong to.
This means that each time you add a "member" node under a "group" (including its email) you will also add the group as a child of the member email, in this other "main node".
More concretely, here is how would be the database structure:
Your current structure:
- groups
- -LB9o....
...
- members
- -LB9qbd....
-email: xxxx#zzz.com
- -LBA7R....
-email: yyyyy#aaaa.com
And the extra structure:
- groupsByMembers
- xxxxxx#zzzcom
- Grupo1: true
- yyyyy#aaaacom
- Grupo1: true
- Grupo2: true
- bbbcccc#dddcom
- Grupo6: true
- Grupo8: true
Note that in the "extra structure" the dots within an email address are removed, since you cannot include a point in a node id. You will have to remove them accordingly when writing and querying.
This way you can easily query for the list of groups a member is belonging to, as shown below. Without the need to loop several times over several items. This dernomalization technique is quite classic in NoSQL databases.
const mailToSearchFor = xxxx.xx#zzz.com;
const ref = database.ref('/groupsByMembers/' + mailToSearchFor.replace(/\./g, ''));
ref.once('value', snapshot => {
const val = snapshot.val();
for (let key in val) {
if (val.hasOwnProperty(key)) {
console.log(key);
}
}
});
In order to write to the two database nodes simultaneously, use the update method as explained here https://firebase.google.com/docs/database/web/read-and-write#update_specific_fields
This is because you have a random key before members, you need to go through the path and not skip a node, to be able to access the values:
ref_db.child("groups").child("-LB9oWcnE0wXx8PbH4D").child("members").orderByChild("email").equalTo(email).once("value", (snapshot)=>{
console.log(snapshot.val());
});
I'm trying to setup a friend system in Firestore. My data model looks like this at the moment:
collection("users") ->
document("user1")
document("user2")
...
A document in the users collection contains data like the name, email... of the user. I'd like to enable a user to have friends now, but I'm unsure about the best way to model this.
So, I'd for sure add a friends field in the documents of the users, but what should this field contain? My first thought was a pointer to a new collection called friends in which the documents are users. Something like this:
collection("users") {
document("user1") {
name:user1,
friends: -> collection("friends") {
document("user2"),
...
}
}
}
This seems reasonable, but that'd mean that I'd have a lot of duplicate data in my database because each user that has friends will be duplicated in a friends collection. Should I worry about this or is this normal in a Firestore database structure?
Would it perhaps be possible to point to a document in the users collection from the friends collection? Something like:
collection("users") {
document("user1") {
name:user1,
friends: -> collection("friends") {
document, -----
... |
} |
}, |
document("user2")<-
}
Or should I throw away the thought of using a collection for friends and just keep a list with uids of all friends of the user?
Seems you are using two separate collections for users and friends first all you can do it by one collection. But I don't want to go there may be there was another scenario.
As your separate collection way, you can design your friends collection model to meet no duplication:
{
name : 'Name',
email : 'email#mail.com'
has_connected : {
'user1' : true // here you can use anyother unique key from user
}
}
The thing is that firestore recommend this types of design for query and for faster performance you can make that has_connected key as index.
In this approach, you have to check during adding new friend by email or any other unique key. if exists then just put another key into has_connected with the respective user. e.g user2 : true.
Finally, for fetching all friends for a user you have to do a query like this: e.g: in javascript
let ref = firebase.firestore().collection("friends");
ref
.where(`has_connected.${username}`, "==", true)
.get()
.then(//do your logic)
.catch()
Thanks
I would like to make a one to one chat. Each user can contact another user.
Json structure would be :
{
"messages" :
"user1UID_user2UID" : {
auto generated ID : {
"text" : "hello",
"timestamp" : 192564646546,
"name" : "user1"
},
auto generated ID : {
"text" : "hi",
"timestamp" : 192564646554,
"name" : "user2"
}
}
}
When user1 connects to the app, he can see the list of every conversation of which he is a part.
Let's say he had initiated a conversation with user 2, and user 3 has a conversation with him too.
So we would have the following children :
user1UID_user2UID
user3UID_user1UID
How can I retrieve all the conversations User1 is involved in to ?
constructor(db: AngularFireDatabase) {
this.messages= db.list('/messages/' + user1UID + "_" + user2UID); //but I don't know user2UID at this moment
}
Can I make a Regex or do I have to store the conversation key (somewhere) every time it concerns him ?
Or I'm completely wrong and I do not look at the problem the right way?
The key naming schema you use for the chat rooms is a variant of my answer here: http://stackoverflow.com/questions/33540479/best-way-to-manage-chat-channels-in-firebase. It's a variant, since you don't seem to order the UIDs lexicographically, which I recommend.
All my proposed algorithm does is generate a reproducible, unique, idempotent key for a chat room between specific users. And while those are very important properties for a data model, they don't magically solve other use-cases.
As often the case in NoSQL data modeling, you'll have to model the data to fit with the use-cases you want. So if your app requires that you show a list of chat rooms for each user, then you should include in your data model a list of chat rooms for each user:
userChatRooms
user1UID
user1UID_user2UID
user1UID_user3UID
user2UID
user1UID_user2UID
user1UID_user3UID
user3UID
user1UID_user3UID
Now getting a list of the chat rooms for a user is as easy as reading /userChatRooms/$uid.
I have a game built on Meteor framework. One game document is something like this:
{
...
participants : [
{
"name":"a",
"character":"fighter",
"weapon" : "sword"
},
{
"name":"b",
"character":"wizard",
"weapon" : "book"
},
...
],
...
}
I want Fighter character not to see the character of the "b" user. (and b character not to see the a's) There are about 10 fields like character and weapon and their value can change during the game so as the restrictions.
Right now I am using Session variables not to display that information. However, it is not a very safe idea. How can I subscribe/publish documents according to the values based on characters?
There are 2 possible solutions that come to mind:
1. Publishing all combinations for different field values and subscribing according to the current state of the user. However, I am using Iron Router's waitOn feature to load subscriptions before rendering the page. So I am not very confident that I can change subscriptions during the game. Also because it is a time-sensitive game, I guess changing subscriptions would take time during the game and corrupt the game pleasure.
My problem right now is the user typing
Collection.find({})
to the console and see fields of other users. If I change my collection name into something difficult to find, can somebody discover the collection name? I could not find a command to find collections on the client side.
The way this is usually solved in Meteor is by using two publications. If your game state is represented by a single document you may have problem implementing this easily, so for the sake of an example I will temporarily assume that you have a Participants collection in which you're storing the corresponding data.
So anyway, you should have one subscription with data available to all the players, e.g.
Meteor.publish('players', function (gameId) {
return Participants.find({ gameId: gameId }, { fields: {
// exclude the "character" field from the result
character: 0
}});
});
and another subscription for private player data:
Meteor.publish('myPrivateData', function (gameId) {
// NOTE: not excluding anything, because we are only
// publishing a single document here, whose owner
// is the current user ...
return Participants.find({
userId: this.userId,
gameId: gameId,
});
});
Now, on the client side, the only thing you need to do is subscribe to both datasets, so:
Meteor.subscribe('players', myGameId);
Meteor.subscribe('myPrivateData', myGameId);
Meteor will be clever enough to merge the incoming data into a single Participants collection, in which other players' documents will not contain the character field.
EDIT
If your fields visibility is going to change dynamically I suggest the following approach:
put all the restricted properties in a separated collection that tracks exactly who can view which field
on client side use observe to integrate that collection into your local player representation for easier access to the data
Data model
For example, the collection may look like this:
PlayerProperties = new Mongo.Collection('playerProperties');
/* schema:
userId : String
gameId : String
key : String
value : *
whoCanSee : [String]
*/
Publishing data
First you will need to expose own properties to each player
Meteor.publish('myProperties', function (gameId) {
return PlayerProperties.find({
userId: this.userId,
gameId: gameId
});
});
then the other players properties:
Meteor.publish('otherPlayersProperties', function (gameId) {
if (!this.userId) return [];
return PlayerProperties.find({
gameId: gameId,
whoCanSee: this.userId,
});
});
Now the only thing you need to do during the game is to make sure you add corresponding userId to the whoCanSee array as soon as the user gets ability to see that property.
Improvements
In order to keep your data in order I suggest having a client-side-only collection, e.g. IntegratedPlayerData, which you can use to arrange the player properties into some manageable structure:
var IntegratedPlayerData = new Mongo.Collection(null);
var cache = {};
PlayerProperties.find().observe({
added: function (doc) {
IntegratedPlayerData.upsert({ _id : doc.userId }, {
$set: _.object([ doc.key ], [ doc.value ])
});
},
changed: function (doc) {
IntegratedPlayerData.update({ _id : doc.userId }, {
$set: _.object([ doc.key ], [ doc.value ])
});
},
removed: function (doc) {
IntegratedPlayerData.update({ _id : doc.userId }, {
$unset: _.object([ doc.key ], [ true ])
});
}
});
This data "integration" is only a draft and can be refined in many different ways. It could potentially be done on server-side with a custom publish method.