We are trying to read specific data sets from Firebase and the current solution we have is this:
let ref = FIRDatabase.database().reference().child("messages")
func retrieveMessageAttributes() {
ref.queryOrderedByKey().queryEqual(toValue: "uniqueFirebaseID").observe(.value, with: { (snapshot) in
print(snapshot)
for item in snapshot.children {
let data = (item as! FIRDataSnapshot).value! as! NSDictionary
print("*********************")
print((data["text"])!)
}
})
This prints all of the data for the specific set in the console, however it seems strange to have to retrieve data, convert it to a hash, and then read specific values.
So we were wondering if anyone else has an alternative method, or ORM, which is simpler and cleaner.
Related
I use the pagination method at the bottom of this question which works fine. Once the startKey is initialized with a key from the db that's the point at which the next pagination will occur from and the next set of posts (children) will get appended to the datasource.
I realized that if that key got deleted by the initial user who posted it, then once I try to paginate from that key since it doesn't exist the children that would get appended if it was there wouldn't get appended because they wouldn't be accessible (they're accessible based on that key).
The only thing I could think of was to first check if the key exists() and if it doesn't just start everything over from the beginning:
if !snapshot.exists() {
self?.startKey = nil
self?.datasource.removeAll()
self?.collectionView.reloadData()
self?.handlePagination()
return
}
It works fine but it's not the most fluid user experience because I'd rather just pull the posts prior to the deleted key (I have no prior reference to them).
A possibility is to just keep an array of all the previous keys and just loop through them but there's always a minute chance that those keys can get deleted by the users who posted them also.
Any ideas of how to get around this?
var startKey: String?
func handlePagination() {
if startKey == nil {
Database...Ref.child("posts")
.queryOrderedByKey()
.queryLimited(toLast: 7)
.observeSingleEvent(of: .value, with: { [weak self](snapshot) in
guard let children = snapshot.children.allObjects.first as? DataSnapshot else { return}
for child in snapshot.children.allObjects as! [DataSnapshot] {
// append child to datasource
}
self?.startKey = children.key
})
} else {
Database...Ref.child("posts")
.queryOrderedByKey()
.queryEnding(atValue: startKey!)
.queryLimited(toLast: 8)
.observeSingleEvent(of: .value, with: { [weak self](snapshot) in
if !snapshot.exists() {
self?.startKey = nil
self?.datasource.removeAll()
self?.collectionView.reloadData()
self?.handlePagination()
return
}
guard let children = snapshot.children.allObjects.first as? DataSnapshot else { return}
for child in snapshot.children.allObjects as! [DataSnapshot] {
// insert child in datasource at startIndex
}
self?.startKey = children.key
})
}
}
there's always a minute chance that those keys can get deleted by the users who posted them also
You're saying that you could keep the keys of the current page, and just loop through until you find an item that was not deleted. In the case that all have been deleted, you'd reach the end of the list of keys, and should create a new query that doesn't have a startAt(). This will give you the first X items, which is the correct behavior in that case I think.
In general though: dealing with realtime and pagination is really hard, which is the main reason the paging adapters in FirebaseUI don't do realtime updates.
I'm trying to append "the retrieved data -Keys- from firebase" into an array but it doesn't work
This is the for loop output #2 the retrieved keys
This the keys from firebase
This is the code
let ref = Database.database().reference()
ref.child("Faculty ").observe(.value, with: { (snapshot) in
if let result = snapshot.children.allObjects as? [DataSnapshot] {
for child in result {
let FacultyName = child.key as! String
print(FacultyName)
self.NamesofFac.append(FacultyName)
}
}
})
for i in 0...self.NamesofFac.count {
print(self.NamesofFac.count)
print(" line")
print(self.NamesofFac)
The problem you are having is the Firebase Observe function give a callback in the form of a (snapshot).
It takes a bit of time to go to the web to get the data, therefore, firebase returns the data asynchronously. Therefore your code in your for loop will run before your firebase data has been returned. At the time your for loop code runs the array is still blank. But the for loop code in a separate function as you see in my sample code and call it straight after your for loop inside your firebase observe call.
Try this instead:
override func viewDidLoad() {
getFirebaseData()
}
func getFirebaseData() {
let ref = Database.database().reference()
ref.child("Faculty ").observe(.value, with: { (snapshot) in
if let result = snapshot.children.allObjects as? [DataSnapshot] {
for child in result {
let FacultyName = child.key as! String
print(FacultyName)
self.NamesofFac.append(FacultyName)
}
printNames()
}
})
}
func printNames() {
for i in 0...self.NamesofFac.count {
print(self.NamesofFac.count)
print(" line")
print(self.NamesofFac)
}
}
This was it won't print the names until they have been fully loaded from firebase.
PS: Your naming conventions are incorrect. You seem to be naming variables with a capital letter. Variables should be camel case. Classes should start with a capital.
I am trying to show my last sent message on my home screen of the chat messenger, from storyboard it looks like :
and the code I used are:
func getAllMsg() {
self.users = []
let fromId = Auth.auth().currentUser!.uid
let ref = Database.database().reference().child("privateMessages").child(fromId)
ref.observeSingleEvent(of: .value) { (snapshot) in
for snap in snapshot.children.allObjects as! [DataSnapshot] {
// retrieving receiver's ID
let chatUserID = snap.key
let ref2 = Database.database().reference().child("users").child(chatUserID)
// to retrieve message ID
ref2.observeSingleEvent(of: .value, with: { (snapshot2) in
let newUser = User(dictionary: snapshot2.value as! [String: AnyObject])
// to get the last message
ref.child(chatUserID).queryLimited(toLast: 1).observeSingleEvent(of: .value, with: { (snapshot3) in
let value = snapshot3.children
while let rest = value.nextObject() as? DataSnapshot {
newUser.lastMessage = (rest.value as! [String: AnyObject])["textMessages"] as? String
self.users.append(newUser)
DispatchQueue.main.async {
self.tableView.reloadData()
}
break
}
})
})
}
}
}
I have done some changes to my database and the above codes works, but after i changed the way i do my database, it doesnt work anymore
previously, my firebase looks like
now my firebase looks like:
i made a chatRoomId by using send and receiver ID. however I am now not able to show my last sent message which was supposed to show on my homescreen. Any ways I can go about this? Or the way I fetched my database is wrong?
Your query is wrong according to your db structure. Also don't perform lastMessage query inside the block of other query because this is totally independent query and not related with any. Below piece of code will work for you.
let ref = kFirDefaultDatabase.reference().child("yourChatRoomId").queryOrdered(byChild: "fromId").queryEqual(toValue: "0YfqnPIOYFYKb8cYZMHnSYti62i2").queryLimited(toLast: 1)
ref.observeSingleEvent(of: DataEventType.value) { (snapshot) in
if snapshot.exists() {
print(snapshot.value)
}
}
This will fetch the last message sent by fromId for the requested chatRoomId. For more detail have a look at Firebase Queries doc.
And if you want to do this in table for all users like in WhatsApp or other chatting application then you will need to make an extra table LastMessages and save last message information here corresponding to each chatRoomId or if possible save this detail somewhere you can fetch with the tableData so that you don't need to query for each chatRoom in a loop.
You can do some better stuff to make it faster. Use CoreData or Sqlite and save/update lastMessage information into local db whenever you send or received any message, where chatRoomId will be a primary key and first get the information from local db and show in the table immediately and mean while you can fetch the data from server and update your local db and refresh the table.
EDIT: For comment to get the last message regardless I send to recipient or recipient send to me.
Remove orderBy query and just use limitToLast. See below code:
let ref = kFirDefaultDatabase.reference().child("yourChatRoomId").queryLimited(toLast: 1)
ref.observeSingleEvent(of: DataEventType.value) { (snapshot) in
if snapshot.exists() {
print(snapshot.value)
}
}
You need to set up rooms differently.
If you you have 3 people in a room, what will the RoomID be ? If someone leaves the room how will you know what the room history is ?
i am a newbie in iOS development, and i am learning a tutorial about read and write data to firebase. I want to retrieve data from Firebase and populate the tableView with it.
I am confused when retrieving the data from real time database using .value data event type when observing the reference. here is the simplified code
class Story
{
var text = ""
var numberOfLikes = 0
var numberOfAngry = 0
let ref: FIRDatabaseReference!
init(snapshot: FIRDataSnapshot)
{
ref = snapshot.ref
if let value = snapshot.value as? [String : Any] {
text = value["text"] as! String
numberOfLikes = value["numberOfLikes"] as! Int
numberOfAngry = value["numberOfAngry"] as! Int
} else {
numberOfAngry = 0
numberOfLikes = 0
}
}
}
class StoriesTableViewController: UITableViewController
{
// MARK: - Properties
var stories = [Story]()
private let storiesRef = FIRDatabase.database().reference().child("stories")
#IBOutlet weak var composeBarButtonItem: UIBarButtonItem!
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
storiesRef.observe(.value, with: { snapshot in
self.stories.removeAll()
for child in snapshot.children {
let story = Story(snapshot: child as! FIRDataSnapshot)
self.stories.append(story)
}
self.tableView.reloadData()
})
}
my questions are...
i have looked other tutorial which almost the same, just write simple data and populate the tableview with it, but the other tutorial just use .childadded as the event type. i don't understand why in this tutorial .value event type is used ? because it looks more complicated.
why we have to loop the snapshot.children ? is snapshot.children is just the same as child when we create database reference?
actually i am not really comfortable with term snapshot(FIRDataSnapshot) and reference (FIRDatabasereference). is there any article or video explaining about this term?
i am sorry if i am asking too many questions and it seems silly, just a rookie who wants to really grasp of this code. Thanks in advance
When you observe the .value event, your completion handler gets called once; with a snapshot of all child nodes. This allows you to handle all child nodes at once, which can be handy to do things like updating counters, or reducing the number of updates to a table view.
When you observe a list of items from the Firebase Database with a .value event, there will potentially be multiple child nodes. So the snapshot contains a list of those results. Even if there is only a single child node, the snapshot will contain a list of one child node. So your completion handler needs to loop over those results, which you do by iterating over snapshot.children.
A FIRDataSnapshot/DataSnapshot is a Firebase object that contains a snapshot of the data you requested at a specific time.
I have an NSArray containing multiple ids. Is there a way in Firebase where I can get all the object with the ids in the array?
I am building a restaurant rating app which uses GeoFire to retrieve nearby restaurants. My problem is that GeoFire only returns a list of ids of restaurant that are nearby. Is there any way i can query for all the object with the ids?
No, you can't do a batch query like that in Firebase.
You will need to loop over your restaurant IDs and query each one using observeSingleEvent. For instance:
let restaurantIDs: NSArray = ...
let db = FIRDatabase.database().reference()
for id in restaurantIDs as! [String] {
db.child("Restaurants").child(id).observeSingleEvent(of: .value) {
(snapshot) in
let restaurant = snapshot.value as! [String: Any]
// Process restaurant...
}
}
If you are worried about performance, Firebase might be able to group all these observeSingleEvent calls and send them as a batch to the server, which may answer your original question after all ;-)
I know that this answer is considered accepted but I have had really good success using promise kit with the method frank posted with his javascript link Speed up fetching posts for my social network app by using query instead of observing a single event repeatedly and just wanted to share the swift version
So I have a list of users ids that are attached to a post like this:
also these methods are in my post class where I have access to the post id from firebase
// this gets the list of ids for the users to fetch ["userid1", "userid2"....]
func getParticipantsIds() -> Promise<[String]> {
return Promise { response in
let participants = ref?.child(self.key!).child("people")
participants?.observeSingleEvent(of: .value, with: { (snapshot) in
guard let snapshotIds = snapshot.value as? [String] else {
response.reject(FirebaseError.noData)
return
}
response.fulfill(snapshotIds)
})
}
}
// this is the individual query to fetch the userid
private func getUserById(id:String) -> Promise<UserData> {
return Promise { response in
let userById = dbRef?.child("users").child(id)
userById?.observeSingleEvent(of: .value, with: { (snapshot) in
guard let value = snapshot.value else {
response.reject(FirebaseError.noData)
return
}
do {
let userData = try FirebaseDecoder().decode(UserData.self, from: value)
response.fulfill(userData)
} catch let error {
response.reject(error)
}
})
}
}
// this is the where the magic happens
func getPostUsers(compeltion: #escaping (_ users:[UserData], _ error:Error?) -> ()){
getParticipantsIds().thenMap { (id) in
return self.getUserById(id: id)
}.done { (users) in
compeltion(users, nil)
}.catch({ error in
compeltion([], error)
})
}