I am using firebase for simple chat application. I am looking to fetch messages of user 1 and user 2. My database structure look like this.
I am using queryOrdered to fetch messages but it will filter with either sender or receiver.
Database.database().reference().child("Chats").queryOrdered(byChild: "receiver")
.queryEqual(toValue: "2WCS7T8dzzNOdhEtsa8jnlbhrl12")
.observe(.value, with: { snapshot in
})
But using this code I got messages of receiver only. How can I receive messages of sender as well. Can I use AND condition to query sender child?
There is no way in your current data structure to with a single query get both the messages that a specific user sent and received.
Firebase Database queries can only order/filter on a single property. In many cases it is possible to combine the values you want to filter on into a single (synthetic) property.
For example, you could combine the sender and receiver UID into a single properties "sender_receiver": "2WCS7T8dzzNOdhEtsa8jnlbhrl12_Sl91z...." and then query for that combined value.
For a longer example of this and other approaches, see my answer here: Query based on multiple where clauses in Firebase
For most chat applications however I recommend creating a database structure that models chat "rooms". So instead of having one long list of all messages, store the messages in rooms/threads, which is also what you show in the UI of your app.
"-RoomId1": {
"msg1": { ... },
"msg2": { ... }
}, "-RoomId2": {
"msg3": { ... },
"msg4": { ... }
}
That way you have the most direct mapping from the database, to what you show on the screen.
For a good way to name the "rooms", see Best way to manage Chat channels in Firebase
You'd then still store a mapping for each user of what rooms they're a part of, which might also be useful in securing access.
I work on iOS app that use firebase real time database, my structure as , I want to write a query that retrieve all users of a group, each user have multiple groups, and each groups have multiple users, I capable of showing all groups of one user and I want to show all other users they are belong to that group, i.e, when user choose of his groups,
How can achieve that?
In my opinion, the best way to deal with this is to duplicate your data. If you definitely need the structure you posted above, you can keep it and create also another one as such:
"groupUsers": {
"123" : { //groupId
"235" : { //uniqueKey for record
userId: "567",
userName: "Jack"
}
}
}
To get all users in a certain group use the firebase reference:
`/groupUsers/${groupId}/`
You loop over the returned list to show values from each list item.
I have an application where user can like photos, comment etc. Functionality like Instagram has.
I want to realize users !feedback!, where user can see information, who liked his photos, who started to follow and etc. I don't know actually how should I organize structure of my database in this situation.
My user node snapshot:
My posts node snapshot:
As I can see, I have next option - I should save all actions, which are linked to user, to his node in internal node Feedback. But how can I keep sync this? For example, someone can follow my user, I will add it to this node, user will unfollow, but the record still remains. I think, that it is wrong way.
I have no other idea actually and I can't find anything about that.
Any suggestions and solutions are much appreciated.
EDIT: I need to understand, how to realize this tab of instagram-like apps:
How to retrieve data for it from nodes?
UPD: DB Architecture in my examples is bad (old question). Be carefull (10.11.2017).
First, let's think about how we need to structure our database for this:
There are two very important principles to follow when structuring data for Firebase:
You should save your data the way you want to retrieve it.
You should keep your data structure as flat as possible - avoid nesting.
Point 1 is because Firebase is not a relational database. This means that we need to keep queries simple in order to achieve performance. Making complex queries might require many requests to Firebase.
Point 2 is because of the way Firebase's query model works: If you observe a node, you also get all the children of that node. This means that, if your data is deeply nested, you might get a lot of data you don't need.
So, having those principles in mind, let's take a look at your case. We have users, who have photos. These are the two primary entities of your database.
I can see that, currently, you are keeping your photos as properties of the users. If you want to be able to query photos by user quickly (remember Point 1), this is a good way to do it. However, if we want users to be able to "favorite" photos, a photo should be more than just a link to its Firebase Storage location: It should also hold other properties, such as which users have favorited it. This property should be an array of user IDs. In addition, for each user, you'll want to store which photos are that user's favorites. This might seem like data duplication, but when using Firebase, it's OK to duplicate some data if it'll lead to simpler queries.
So, using a data index such as in the example above, each of your Photos should look like this:
{
id: /* some ID */,
location: /* Firebase Storage URL */,
favorited_by: {
/* some user ID */: true /* this value doesn't matter */,
/* another user ID */: true,
},
/* other properties... */
}
And your user should have a favorites property listing photo IDs. Now, since every photo has a user that "owns" it, we don't need to have a unique ID for every photo, we just need to ensure that no user has two photos with the same ID. This way, we can refer to the photo by a combination of its user ID and its photo ID.
Of course, remember Point 1: If you want to be able to get user info without getting a user's photos, you should have a different property on your root object for photos instead of associating photos with users. However, for this answer, I'll try to stick to your current model.
Based on what I said above, the favorites property of a user would hold an array of values of the format 'userId/photoId'. So, for instance, if a user favorites the photo with ID "3A" of the user with ID "CN7v0A2", their favorites array would hold the value 'CN7v0A2/3A'. This concludes our structure for favorites.
Now, let's look at what some operations you have mentioned would look like under this structure:
User favorites a photo:
We get the user ID of the photo's owner
We get the user ID of the user who is favoriting the photo
We get the ID of the photo
We add the user who is favoriting's ID to the photo's favorited_by array
We add photoOwnerID + "/" photoID to the favoriting user's favorites array
If the user unfavorites the photo later, we just do the opposite: We remove photoOwnerID + "/" + photoID from the user's favorites and we remove the favoriting user's ID from the photo's favorited_by property.
This kind of logic is sufficient to implement likes, favorites, and follows. Both the follower/liker/favoriter and the followee/likee/favoritee should hold references to the other party's ID, and you should encapsulate the "like/favorite/follow" and "unlike/favorite/unfollow" operations so that they keep that database state consistent every time (this way, you won't run into any issues such as the case you mentioned, where a user unfollows an user but the database still holds the "following" record).
Finally, here's some code of how you could do the "Favorite" and "Unfavorite" operations, assuming you have a User model class:
extension User {
func follow(_ otherUser: User) {
let ref = FIRDatabase.database().reference()
ref.child("users/\(otherUser.userId)/followers/")
.child(self.userId).setValue(true)
ref.child("user/\(self.userId)/following/")
.child(otherUser.userId).setValue(true)
}
func unfollow(_ otherUser: User) {
let ref = FIRDatabase.database().reference()
ref.child("users/\(otherUser.userId)/followers/")
.child(self.userId).remove()
ref.child("user/\(self.userId)/following/")
.child(otherUser.userId).remove()
}
}
Using this model, you can get all the follower user IDs for a user querying that user's followers property and using the .keys() method on the resulting snapshot, and conversely for users a given user follows.
Added content: We can build further on this structure in order to add simple logging of actions, which seems to be what you want to have available to the user in the "Feedback" tab. Let's assume we have a set of actions, such as liking, favoriting and following, which we want to show feedback for.
We'll follow point 1 once again: In order to structure feedback data, it is best to store this data in the same way we want to retrieve it. In this case, we will be most often showing a user their own feedback data. This means we should probably store feedback data by user ID. Additionally, following point 2, we should store feedback data as its own table, instead of adding it to the user records. So we should make a new table on our root object, where for each user ID, we store a list of feedback entries.
It should look something like this:
{
feedback: {
userId1: /* this would be an actual user ID */ {
autoId1: /* generated using Firebase childByAutoId */ {
type: 'follow',
from: /* follower ID */,
timestamp: /* Unix time */,
},
autoId2: {
type: 'favorite',
from: /* ID of the user who favorited the photo */
on: /* photo ID */
timestamp: /* Unix time */
},
/* ...other feedback items */
},
userId2: { /* ...feedback items for other user */ },
/* ...other user's entries */
},
/* other top-level tables */
}
In addition, we will need to change the favorites/likes/follows tables. Before, we were just storing true in order to signal that someone liked or favorited a photo or followed a user. But since the value we use is irrelevant, as we only check keys to find what the user has favorited or liked and who they have followed, we can start using the ID of the entry for the like/favorite/follow. So we would change our "follow" logic to this:
extension User {
func makeFollowFeedbackEntry() -> [String: Any] {
return [
"type": "follow",
"from": self.userId,
"timestamp": UInt64(Date().timeIntervalSince1970)
]
}
func follow(_ otherUser: User) {
let otherId = otherUser.userId
let ref = FIRDatabase.database().reference()
let feedbackRef = ref.child("feedback/\(otherId)").childByAutoId()
let feedbackEntry = makeFollowFeedbackEntry(for: otherId)
feedbackRef.setValue(feedbackEntry)
feedbackRef.setPriority(UInt64.max - feedbackEntry["timestamp"])
let feedbackKey = feedbackRef.key
ref.child("users/\(otherUser.userId)/followers/")
.child(self.userId).setValue(feedbackKey)
ref.child("user/\(self.userId)/following/")
.child(otherUser.userId).setValue(feedbackKey)
}
func unfollow(_ otherUser: User, completionHandler: () -> ()) {
let ref = FIRDatabase.database().reference()
let followerRef = ref.child("users/\(otherUser.userId)/followers/")
.child(self.userId)
let followingRef = ref.child("user/\(self.userId)/following/")
.child(otherUser.userId)
followerRef.observeSingleEvent(of: .value, with: { snapshot in
if let followFeedbackKey = snapshot.value! as? String {
// we have an associated follow entry, delete it
ref.child("feedback").child(otherUser.userId + "/" + followFeedbackKey).remove()
} // if the key wasn't a string, there is no follow entry
followerRef.remove()
followingRef.remove()
completionHandler()
})
}
}
This way, we can get a user's "feedback" just by reading the "feedback" table entry with that user's ID, and since we used setPriority, it will be sorted by the most recent entries first, meaning we can use Firebase's queryLimited(toFirst:) to get only the most recent feedback. When a user unfollows, we can easily delete the feedback entry which informed the user that they had been followed. You can also easily add extra fields to store whether the feedback entry has been read, etc.
And even if you were using the other model before (setting "followerId" to true), you can still use feedback entries for new entries, just check if the value as "followerId" is a string as I have done above :)
You can use this same logic, just with different fields in the entry, to handle favorites and likes. When you handle it in order to show data to the user, just check the string in the "type" field to know what kind of feedback to show. And finally, it should be easy to add extra fields to each feedback entry in order to store, for instance, whether the user has seen the feedback already or not.
You can sort of implement what you want by using Firebase Functions. Here's roughly how I would go about implementing it:
All a user's feedback will be stored in /Feedback/userID/, located at the root.
Within this node, have a subnode called eventStream.
Whenever an action occurs, this can be directly added to the user's eventStream, ordered by time.
This action could be of the form: pushID: { actionType:"liked", post:"somePostID", byUser:"someUserId" }
Also include an anti-action subnode (under /Feedback/userID/). Whenever one of these 'anti-action' events occurs (for example: unlike, unfollow etc.), store this under the anti-action node for the corresponding user. This node will essentially act as a buffer for our function to read from.
This anti-action could be of an almost identical form: pushID: { actionType:"unliked", post:"somePostID", byUser:"someUserId" }
Now for the function.
Whenever an anti-action is added to the anti-action node, a function removes this from the anti-action node, finds the corresponding action in the eventStream, and removes this. This can be achieved easily by first querying by "actionType" then "someUserId" and then by "somePostID".
This will ensure that the user's eventStream will always be up to date with the latest events.
Hope this helps! :)
My app's db has a many to many relationship between a Feed object and a Tweet object. This is to keep track of which feeds every tweet belongs in. If you're familiar with Twitter, imagine the main feed, a list feed, a user profile feed, etc.
How can I make a query using an NSPredicate to get a list of Tweets that exist in a specific Feed (and, inversely, get a list of Feeds that a Tweet exists in)? It seems that queries on inverse relationships does not work in Realm, so what are my options?
If I understand your question correctly this part of the documentation should be helpful:
Inverse Relationships Links are unidirectional. So if a to-many
property Person.dogs links to a Dog instance and a to-one property
Dog.owner links to Person, these links are independent from one
another. Appending a Dog to a Person instance’s dogs property, doesn’t
automatically set the dog’s owner property to this Person. Because
manually synchronizing pairs of relationships is error prone, complex
and duplicates information, Realm exposes an API to retrieve backlinks
described below.
With inverse relationships, you can obtain all objects linking to a
given object through a specific property. For example, calling
Object().linkingObjects(_:forProperty:) on a Dog instance will return
all objects of the specified class linking to the calling instance
with the specified property.
I guess you can do something like:
//assuming your Tweet object has a property like "let feeds = List<Feed>()"
someTweet.linkingObjects(Feed.self, forProperty: "feeds") //should return feeds your Tweet is in
But still I don't think I understand your question clearly. From my point of view your first requirement:
get a list of Tweets that exist in a specific Feed
should have a straightforward solution such as having a property in your Feed object like:
let tweets = List<Tweet>()
I wish you can clarify your situation further.
I wonder if it's possible to simplify the model a bit so many-to-many isn't necessary.
My understanding of Twitter is that tweets aren't 'owned' by any feeds. They simply exist on the platform, and are referenced by any number of feeds, but don't actually belong to any specific feed.
So a model setup like this should be appropriate:
class Tweet : Object {
}
class Feed : Object {
let tweets = List<Tweet>()
}
You can do a reverse lookup on a Tweet to see if there are any feeds in which it is currently visible, and you can simply use the tweets property of Feed objects to see which tweets they're displaying
Since the linkingObjects reverse lookup method of Realm simply returns a standard Swift Array, if you did want to filter that further, you could just use the system APIs (like filter or map) to refine it further.
Otherwise, if you really do want to be able to use Realm's NSPredicate filtering system both ways, then, as messy as it is, you would need to manually have each model linking to a list of the other:
class Tweet : Object {
let feeds = List<Feed>()
}
class Feed : Object {
let tweets = List<Tweet>()
}
While it's not recommended (Since it adds additional work), it's not disallowed.
Good luck!
I have a Firebase array called products that contains items like this one:
JhMIecX5K47gt0VaoQN: {
brand: "Esprit"
category: "Clothes",
gender: "Boys",
name: "Pants",
}
Is it possible to query products from this array using multiple filters with the Firebase API. For example I might want to filter by brand and category (all "Pants" by "Esprit"). So far I've tried ordering by child key and then limiting the start and end of this ordering, but I can't figure out how to apply more filters.
I'm using the iOS SDK.
Firebase can only order/filter on one property (or value) at a time. If you call a orderBy... method multiple times in a single query it will raise an error to indicate this is not allowed.
Actually, in Firebase, when you order by a specific key, there is another index involved : push IDs (if you use them) They are almost perfectly ordered chronologically, so you order by field XXX plus Time.
More details here
In your case, this is not about time, so the only solution is to use additional composite indexes :
JhMIecX5K47gt0VaoQN: {
brand: "Esprit"
category: "Clothes",
brandcategoryIndex: "EspritClothes",
categorybrandIndex: "ClothesEsprit",
brandnameIndex: "EspritPants",
namebrandIndex: "PantsEsprit",
gender: "Boys",
name: "Pants",
}
In the above example, you can query by :
Category > Brand (and the other way)
Name > Brand (and the other way)
Just make sure you add those fields to your Firebase index in the rules section, and that you maintain them anytime the items are modified.
(this process of adding a cost of redundant data at the benefit of performance, which is forced by Firebase in this case, is called denormalization)