I have the following code and was wondering why it crashes the app, I was hoping you could help me figure out what was going on.
The code below is not exact aside from the spinner code.
The idea is to have the spinner racePicker's array populated by FireStore document IDs, as shown below:
val db = FirebaseFirestore.getInstance()
val raceArray = ArrayList()
raceArray.add("Select race...")
db.collection("races").get().addOnSuccessListener {
DocumentSnapshot ->
for (document in DocumentSnapshot) {
raceArray.add(document.id)
Log.e("info", "raceArray contains values $raceArray")
}
This is a rough approximation. I may have set it .toString() or maybe used .addAll vs .add in the raceArray statement.
(I honestly don't remember exactly if this is how I coded it, but it's close enough to give an idea, I'm typing from memory at the moment).
My intention was to use it like so:
racPicker.onSelectedItemListener = object :
OnItemSelectedListener {
override fun onNothingSelected() {
}
override fun onItemSelected(parent: AdapterView<*>?, view:
View?, position: Int, id: Long) {
val selection = parent?.getItemAtPosition(position).toString()
when (selection) {
"$selection" -> raceArray.remove("Select race...").also{
statAllocator(selection) }
}
}
}
For some reason it crashes, but if I assign a literal such as "race name" -> fun, "2nd race name" -> fun, etc it works.
Would it be better to use
if (selectedItem.equals("$selection") {
// do stufd
}
instead? Or is it absolutely necessary to call each and every when case/statement as a literal string? I essentially am looking for a way to have the spinner's selected item (which is an array of document names generated from FireStore database) then "check for itself" and trigger the other functions.
Related
I have been getting this problem now a few times when I'm coding and I think I just don't understand the way SwiftUI execute the order of the code.
I have a method in my context model that gets data from Firebase that I call in .onAppear. But the method doesn't execute the last line in the method after running the whole for loop.
And when I set breakpoints on different places it seems that the code first is just run through without making the for loop and then it returns to the method again and then does one run of the for loop and then it jumps to some other strange place and then back to the method again...
I guess I just don't get it?
Has it something to do with main/background thread? Can you help me?
Here is my code.
Part of my UI-view that calls the method getTeachersAndCoursesInSchool
VStack {
//Title
Text("Settings")
.font(.title)
Spacer()
NavigationView {
VStack {
NavigationLink {
ManageCourses()
.onAppear {
model.getTeachersAndCoursesInSchool()
}
} label: {
ZStack {
// ...
}
}
}
}
}
Here is the for-loop of my method:
//Get a reference to the teacher list of the school
let teachersInSchool = schoolColl.document("TeacherList")
//Get teacherlist document data
teachersInSchool.getDocument { docSnapshot, docError in
if docError == nil && docSnapshot != nil {
//Create temporary modelArr to append teachermodel to
var tempTeacherAndCoursesInSchoolArr = [TeacherModel]()
//Loop through all FB teachers collections in local array and get their teacherData
for name in teachersInSchoolArr {
//Get reference to each teachers data document and get the document data
schoolColl.document("Teachers").collection(name).document("Teacher data").getDocument {
teacherDataSnapshot, teacherDataError in
//check for error in getting snapshot
if teacherDataError == nil {
//Load teacher data from FB
//check for snapshot is not nil
if let teacherDataSnapshot = teacherDataSnapshot {
do {
//Set local variable to teacher data
let teacherData: TeacherModel = try teacherDataSnapshot.data(as: TeacherModel.self)
//Append teacher to total contentmodel array of teacherdata
tempTeacherAndCoursesInSchoolArr.append(teacherData)
} catch {
//Handle error
}
}
} else {
//TODO: Error in loading data, handle error
}
}
}
//Assign all teacher and their courses to contentmodel data
self.teacherAndCoursesInSchool = tempTeacherAndCoursesInSchoolArr
} else {
//TODO: handle error in fetching teacher Data
}
}
The method assigns data correctly to the tempTeacherAndCoursesInSchoolArr but the method doesn't assign the tempTeacherAndCoursesInSchoolArr to self.teacherAndCoursesInSchool in the last line. Why doesn't it do that?
Most of Firebase's API calls are asynchronous: when you ask Firestore to fetch a document for you, it needs to communicate with the backend, and - even on a fast connection - that will take some time.
To deal with this, you can use two approaches: callbacks and async/await. Both work fine, but you might find that async/await is easier to read. If you're interested in the details, check out my blog post Calling asynchronous Firebase APIs from Swift - Callbacks, Combine, and async/await | Peter Friese.
In your code snippet, you use a completion handler for handling the documents that getDocuments returns once the asynchronous call returns:
schoolColl.document("Teachers").collection(name).document("Teacher data").getDocument { teacherDataSnapshot, teacherDataError in
// ...
}
However, the code for assigning tempTeacherAndCoursesInSchoolArr to self.teacherAndCoursesInSchool is outside of the completion handler, so it will be called before the completion handler is even called.
You can fix this in a couple of ways:
Use Swift's async/await for fetching the data, and then use a Task group (see Paul's excellent article about how they work) to fetch all the teachers' data in parallel, and aggregate them once all the data has been received.
You might also want to consider using a collection group query - it seems like your data is structure in a way that should make this possible.
Generally, iterating over the elements of a collection and performing Firestore queries for each of the elements is considered a bad practice as is drags down the performance of your app, since it will perform N+1 network requests when instead it could just send one single network request (using a collection group query).
Terminating app due to uncaught exception 'RLMException', reason: 'Attempting to modify object outside of a write transaction - call beginWriteTransaction on an RLMRealm instance first.'
All changes to a managed object (addition, modification and deletion) must be done within a write transaction. For example,
// Update an object with a transaction
try! realm.write {
author.name = "Thomas Pynchon"
}
I can make a Realm sub-class conform to ObservableObject. However, I don't see how to make the realm properties updatable in SwiftUI. Realm property example below.
#objc dynamic var myName: String = "Adam"
Realm automagically sets up the schema based on #objc dynamic var. I don't see a way to get #Published on a realm property. SwiftUI will render a TextField, but crashes when the value is edited.
TextField("Quantity (\(shoppingItem.myUnit!.myName))", value: $shoppingItem.stdQty, formatter: basicFormat)
.textFieldStyle(RoundedBorderTextFieldStyle())
.keyboardType(.numbersAndPunctuation)
Is there any way to wrap SwiftUI state changes inside a Realm write transaction?
Another way to do this is to use a Custom Binding, and when setting the property, open a transaction and save data to realm.
TextField("Quantity (\(shoppingItem.myUnit!.myName))",
value: Binding(get: {shoppingItem.stdQty},
set: {(value) in
//if your state property is in a view model, all this code could be like viewModel.saveData(newMessage: value)
let realm = try! Realm()
try! realm.write {
shoppingItem.stdQty = value
}
}),
formatter: basicFormat)
.textFieldStyle(RoundedBorderTextFieldStyle())
.keyboardType(.numbersAndPunctuation)
This will save to realm on every character inserted
Consider the Realm property, stdQty shown below. It can only be changed within a write transaction.
import RealmSwift
import Combine
class ShoppingItems: Object, ObservableObject
let objectWillChange = PassthroughSubject<Void, Never>()
#objc dynamic var stdQty: Double = 1
You cannot bind stdQty without the error in the original question. However you can create a calculated variable that can be bound.
var formQty: Double {
get {
return stdQty
}
set {
objectWillChange.send()
if let sr = self.realm {
try! sr.write {
stdQty = newValue
}
}
}
}
Binding the calculated variable works fine.
TextField("Quantity (\(shoppingItem.myUnit!.myName))", value: $shoppingItem.formQty, formatter: basicFormat)
.textFieldStyle(RoundedBorderTextFieldStyle())
.keyboardType(.numbersAndPunctuation)
Answer limitation: objectWillChange is only triggered by the calculated variable. Changes in the form are reflected in the form. Changes in the realm don't trigger a Combine objectWillChange yet.
I have a class Market which contains a collection of MarketUpdate objects called m_updates. For the UI I am using type-safe builders to create columns in a tableview like so:
override val root = tableview<Market> {
val sortedMarketList = SortedList<Market>(markets)
sortedMarketList.comparatorProperty().bind(this.comparatorProperty())
items = sortedMarketList
...
column("Strikes", Market::m_strikes)
...
The m_strikes property is just a SimpleIntegerProperty directly owned by a Market object. However, I need to be able to build columns like these:
...
column("Created At", Market::m_updates::first::m_time)
...
...
column("Last Update", Market::m_updates::last::m_time)
...
where m_time is a SimpleLongProperty owned by a MarketUpdate object. When a Market object is updated, a new MarketUpdate object is added to the end of the m_updates collection. This means that the binding needs to automatically transition from one object to another, and that the tableview needs to be notified and update itself to reflect the data in the new object. I think binding by way of the first() and last() functions of the collection as described above captures the idea in a very simple way, but it won't compile.
There are many properties like m_strikes and m_time. How can I achieve this gracefully?
If I understand your use case, what you want to do is to create an observable value that represents the time property for the first and last updates in a given Market object. To do that, you can create an objectBinding based on the updates list inside of each Market object, then extract the first() or last() element's timeProperty. In the following example, the TableView will update as soon as you augment the updates list in any Market object.
Bear in mind that the example requires each Market to have at least one update. If this isn't your case, make sure to handle null accordingly.
class Market {
val updates = FXCollections.observableArrayList<MarketUpdate>()
}
class MarketUpdate {
val timeProperty = SimpleObjectProperty(LocalDateTime.now())
}
class MarketList : View("Markets") {
val markets = FXCollections.observableArrayList<Market>()
val data = SortedFilteredList<Market>(markets)
override val root = borderpane {
prefWidth = 500.0
center {
tableview(markets) {
column<Market, LocalDateTime>("Created at", { objectBinding(it.value.updates) { first() }.select { it!!.timeProperty } })
column<Market, LocalDateTime>("Last update", { objectBinding(it.value.updates) { last() }.select { it!!.timeProperty } })
}
}
bottom {
toolbar {
// Click to add an update to the first entry
button("Add update").action {
markets.first().updates.add(MarketUpdate())
}
}
}
}
init {
// Add some test entries
markets.addAll(
Market().apply { updates.addAll(MarketUpdate(), MarketUpdate(), MarketUpdate()) },
Market().apply { updates.addAll(MarketUpdate(), MarketUpdate(), MarketUpdate()) },
Market().apply { updates.addAll(MarketUpdate(), MarketUpdate(), MarketUpdate()) },
Market().apply { updates.addAll(MarketUpdate(), MarketUpdate(), MarketUpdate()) }
)
}
}
I've used a SortedFilteredList to make it easier to deal with sorting. The reason sort works here, is that the columns are actually represented by LocalDateTime values.
I hope this gives you some ideas :)
I can not make a simple select on a SQLite database, via GRDB.swift
Here is my code:
override func viewDidLoad()
{
super.viewDidLoad()
do
{
let dbQueue = try DatabaseQueue(path: "games.sqlite")
try dbQueue.inDatabase
{
db in try db.execute("SELECT * FROM games")
}
}
catch
{
print("Erreur !")
}
}
I do not find in the documentation a simple way to perform a simple select, the doc speaks of model, and I desire just for the moment to make direct queries.
The documentation speaks only for error on my part of model.
Thank you all for your help.
My environment :
Xcode8.2.1
swift3
cocoapods 1.2.0.rc.1
The GRDB documentation says:
Once granted with a database connection, the execute method executes the SQL statements that do not return any database row, such as CREATE TABLE, INSERT, DELETE, ALTER, etc.
So if you want to fetch rows, you picked the wrong method.
To fetch rows, you use a fetching method (which starts with fetch), as documented in the Row Queries documentation chapter, that I encourage you to read.
For example:
let rows = try dbQueue.inDatabase { db in
try Row.fetchAll(db, "SELECT * FROM games")
}
// Now we're back to the main thread: use rows:
for row in rows {
let name: String = row.value(named: "name")
let year: Int = row.value(named: "year")
print(name)
print(year)
}
That's what it gives "without going through models".
Yet models are still handy:
let games = try dbQueue.inDatabase { db -> [Game] in
let rows = try Row.fetchAll(db, "SELECT * FROM games")
return rows.map { row in
Game(
name: row.value(named: "name"),
year: row.value(named: "year"))
}
}
// Now we're back to the main thread: use games
for game in games {
print(game.name)
print(game.year)
}
If you have your Game type (struct or class) adopt the RowConvertible protocol, you can even write:
let games = try dbQueue.inDatabase { db in
try Game.fetchAll(db, "SELECT * FROM games")
}
And if Game also adopts TableMapping protocol, you get:
let games = try dbQueue.inDatabase { try Game.fetchAll($0) }
See Record for the documentation of those protocols.
I'm trying to work with associating documents in different collections (not embedded documents) and while there is an issue for that in Mongooose, I'm trying to work around it now by lazy loading the associated document with a virtual property as documented on the Mongoose website.
The problem is that the getter for a virtual takes a function as an argument and uses the return value for the virtual property. This is great when the virtual doesn't require any async calls to calculate it's value, but doesn't work when I need to make an async call to load the other document. Here's the sample code I'm working with:
TransactionSchema.virtual('notebook')
.get( function() { // <-- the return value of this function is used as the property value
Notebook.findById(this.notebookId, function(err, notebook) {
return notebook; // I can't use this value, since the outer function returns before we get to this code
})
// undefined is returned here as the properties value
});
This doesn't work since the function returns before the async call is finished. Is there a way I could use a flow control library to make this work, or could I modify the first function so that I pass the findById call to the getter instead of an anonymous function?
You can define a virtual method, for which you can define a callback.
Using your example:
TransactionSchema.method('getNotebook', function(cb) {
Notebook.findById(this.notebookId, function(err, notebook) {
cb(notebook);
})
});
And while the sole commenter appears to be one of those pedantic types, you also should not be afraid of embedding documents. Its one of mongos strong points from what I understand.
One uses the above code like so:
instance.getNotebook(function(nootebook){
// hey man, I have my notebook and stuff
});
While this addresses the broader problem rather than the specific question, I still thought it was worth submitting:
You can easily load an associated document from another collection (having a nearly identical result as defining a virtual) by using Mongoose's query populate function. Using the above example, this requires specifying the ref of the ObjectID in the Transaction schema (to point to the Notebook collection), then calling populate(NotebookId) while constructing the query. The linked Mongoose documentation addresses this pretty thoroughly.
I'm not familiar with Mongoose's history, but I'm guessing populate did not exist when these earlier answers were submitted.
Josh's approach works great for single document look-ups, but my situation was a little more complex. I needed to do a look-up on a nested property for an entire array of objects. For example, my model looked more like this:
var TransactionSchema = new Schema({
...
, notebooks: {type: [Notebook]}
});
var NotebookSchema = new Schema({
...
, authorName: String // this should not necessarily persist to db because it may get stale
, authorId: String
});
var AuthorSchema = new Schema({
firstName: String
, lastName: String
});
Then, in my application code (I'm using Express), when I get a Transaction, I want all of the notebooks with author last name's:
...
TransactionSchema.findById(someTransactionId, function(err, trans) {
...
if (trans) {
var authorIds = trans.notebooks.map(function(tx) {
return notebook.authorId;
});
Author.find({_id: {$in: authorIds}, [], function(err2, authors) {
for (var a in authors) {
for (var n in trans.notebooks {
if (authors[a].id == trans.notebooks[n].authorId) {
trans.notebooks[n].authorLastName = authors[a].lastName;
break;
}
}
}
...
});
This seems wildly inefficient and hacky, but I could not figure out another way to accomplish this. Lastly, I am new to node.js, mongoose, and stackoverflow so forgive me if this is not the most appropriate place to extend this discussion. It's just that Josh's solution was the most helpful in my eventual "solution."
As this is an old question, I figured it might use an update.
To achieve asynchronous virtual fields, you can use mongoose-fill, as stated in mongoose's github issue: https://github.com/Automattic/mongoose/issues/1894