I'm trying to write code that will be executed if an SQLite query won't return results. However, the async nature of Node.js makes this difficult. I don't know if I can write code inside the callback function, because when I test with inputs that will cause empty results, nothing happens.
I'm doing
db.each("SELECT pid, collection , photo FROM photos WHERE collection = '"+collection_id+"' AND pid = '"+photo_id+"' ", function(err, row) {
console.log("PHOTO FOUND");
//code inside the callback function
});
//code I want
Specifically, I want to render something general, in case the user requests something that is not in the db
What should I do?
This is from the API documentation for the package you appear to be using (emphasis mine):
Database#each(sql, [param, ...], [callback], [complete])
Runs the SQL query with the specified parameters and calls the callback with for each result row. The function returns the Database object to allow for function chaining. The parameters are the same as the Database#run function, with the following differences:
The signature of the callback is function(err, row) {}. If the result set succeeds but is empty, the callback is never called. In all other cases, the callback is called once for every retrieved row. The order of calls correspond exactly to the order of rows in the result set.
After all row callbacks were called, the completion callback will be called if present. The first argument is an error object, and the second argument is the number of retrieved rows. If you specify only one function, it will be treated as row callback, if you specify two, the first (== second to last) function will be the row callback, the last function will be the completion callback.
If you know that a query only returns a very limited number of rows, it might be more convenient to use Database#all to retrieve all rows at once.
So, it would seem your code should look like this:
var sql = "SELECT pid, collection , photo FROM photos WHERE collection = '"+collection_id+"' AND pid = '"+photo_id+"' ";
db.each(sql, function(err, row) {
console.log("PHOTO FOUND");
//code inside the callback function
}, function(err, rows) {
if (rows == 0) {
//code I want
}
});
Related
To optimize usage, I have a Firestore collection with only one document, consisting in a single field, which is an array of strings.
This is what the data looks like in the collection. Just one document with one field, which is an array:
On the client side, the app is simply retrieving the entire status document, picking one at random, and then sending the entire array back minus the one it picked
var all = await metaRef.doc("status").get();
List tokens=all['all'];
var r=new Random();
int numar=r.nextInt(tokens.length);
var ales=tokens[numar];
tokens.removeAt(numar);
metaRef.doc("status").set({"all":tokens});
Then it tries to do some stuff with the string, which may fail or succeed. If it succeeds, then no more writing to the database, but if it fails it fetches that array again, adds the string back and pushes it:
var all = await metaRef.doc("status").get();
List tokens=all['all'];
List<String> toate=(tokens.map((element) => element as String).toList());
toate.add(ales.toString());
metaRef.doc("status").set({"all":toate});
You can use the methods associated with the Set object.
Here is an example to check that only 1 item was removed:
allow update: if checkremoveonlyoneitem()
function checkremoveonlyoneitem() {
let set = resource.data.array.toSet();
let setafter = request.resource.data.array.toSet();
return set.size() == setafter.size() + 1
&& set.intersection(setafter).size() == 1;
}
Then you can check that only one item was added. And you should also add additional checks in case the array does not exist on your doc.
If you are not sure about how the app performs the task i.e., successfully or not, then I guess it is nice idea to implement this logic in the client code. You can just make a simple conditional block which deletes the field from the document if the operation succeeds, either due to offline condition or any other issue. You can find the following sample from the following document regarding how to do it. Like this, with just one write you can delete the field which the user picks without updating the whole document.
city_ref = db.collection(u'cities').document(u'BJ')
city_ref.update({
u'capital': firestore.DELETE_FIELD
})snippets.py
I am trying to grab information from my firebase database after a particular intent is invoked in my conversation flow.
I am trying to make a function which takes a parameter of user ID, which will then get the highscore for that user, and then say that users highscore back to them.
app.intent('get-highscore', (conv) => {
var thisUsersHighestscore = fetchHighscoreByUserId(conv.user.id);
conv.ask('your highest score is ${thisUsersHighestScore}, say continue to keep playing.');
});
function fetchHighscoreByUserId(userId){
var highscoresRef = database.ref("highscores");
var thisUsersHighscore;
highscoresRef.on('value',function(snap){
var allHighscores= snap.val();
thisUsersHighscore = allHighscores.users.userId.highscore;
});
return thisUsersHighscore;
}
An example of the data in the database:
"highscores" : {
"users" : {
"1539261356999999924819020" : {
"highscore" : 2,
"nickname" : "default"
},
"15393362381293223232222738" : {
"highscore" : 78,
"nickname" : "quiz master"
},
"15393365724084067696560" : {
"highscore" : "32",
"nickname" : "cutie pie"
},
"45343453535534534353" : {
"highscore" : 1,
"nickname" : "friendly man"
}
}
}
It seems like it is never setting any value to thisUsersHighScore in my function.
You have a number of issues going on here - both with how you're using Firebase, how you're using Actions on Google, and how you're using Javascript. Some of these issues are just that you could be doing things better and more efficiently, while others are causing actual problems.
Accessing values in a structure in JavaScript
The first problem is that allHighscores.users.userId.highscore means "In an object named 'allHighscores', get the property named 'users', from the result of that, get the property named 'userId'". But there is no property named "userId" - there are just a bunch of properties named after a number.
You probably wanted something more like allHighscores.users[userId].highscore, which means "In an object named 'allHighscores', get the property named 'users', fromt he result of that, get the property named by the value of 'userId'".
But if this has thousands or hundreds of thousands of records, this will take up a lot of memory. And will take a lot of time to fetch from Firebase. Wouldn't it be better if you just fetched that one record directly from Firebase?
Two Firebase Issues
From above, you should probably just be fetching one record from Firebase, rather than the whole table and then searching for the one record you want. In firebase, this means you get a reference to the path of the data you want, and then request the value.
To specify the path you want, you might do something like
var userRef = database.ref("highscores/users").child(userId);
var userScoreRef = userRef.child( "highscore" );
(You can, of course, put these in one statement. I broke them up like this for clarity.)
Once you have the reference, however, you want to read the data that is at that reference. You have two issues here.
You're using the on() method, which fetches the value once, but then also sets up a callback to be called every time the score updates. You probably don't need the latter, so you can use the once() method to get the value once.
You have a callback function setup to get the value (which is good, since this is an async operation, and this is the traditional way to handle async operations in Javascript), but you're returning a value outside of that callback. So you're always returning an empty value.
These suggest that you need to make fetchHighScoreByUserId() an asynchronous function as well, and the way we have to do this now is to return a Promise. This Promise will then resolve to an actual value when the async function completes. Fortunately, the Firebase library can return a Promise, and we can get its value as part of the .then() clause in the response, so we can simplify things a lot. (I strongly suggest you read up on Promises in Javascript and how to use them.) It might look something like this:
return userScoreRef.once("value")
.then( function(scoreSnapshot){
var score = scoreSnapshot.val();
return score;
} );
Async functions and Actions on Google
In the Intent Handler, you have a similar problem as above. The call to fetchHighScoreByUserId() is async, so it doesn't finish running (or returning a value) by the time you call conv.ask() or return from the function. AoG needs to know to wait for an async call to finish. How can it do that? Promises again!
AoG Intent Handlers must return a Promise if there is an asyc call involved.
Since the modified fetchHighScoreByUserId() returns a Promise, we will leverage that. We'll also set our response in the .then() part of the Promise chain. It might look something like this:
app.intent('get-highscore', (conv) => {
return fetchHighscoreByUserId(conv.user.id)
.then( function(highScore){
conv.ask(`Your highest score is ${highScore}. Do you want to play again?`);
} );
});
Two asides here:
You need to use backticks "`" to define the string if you're trying to use ${highScore} like that.
The phrase "Say continue if you want to play again." is a very poor Voice User Interface. Better is directly asking if they want to play again.
I have successfully integeraed meteor with angular2 but while fetching the data from collection facing difficulties in getting at one shot, here is the steps:
Collection Name : OrderDetails
No Of records : 1000
Server:
Created publication file to subcribe the collection:
Meteor.publish('orderFilter', function() {
return OrderLineDetails.find({});
});
Client:
this.dateSubscription =
MeteorObservable.subscribe('orderFilter').subscribe(()=> {
let lines = OrderDetails.find({expectedShipDate:{$in:strArr}},{fields:
{"expectedShipDate":1,"loadNo":1},sort:{"expectedShipDate":1}}).fetch();
});
In this lines attribute fetches all the collection entries, but fails to subscribe for the changes
When I try with below one,
OrderDetails.find({expectedShipDate:{$in:strArr}},{fields:{"expectedShipDate":1,"loadNo":1},sort:{"expectedShipDate":1}}).zone().subscribe(results => {
// code to loop the results
});
In this am able to subscribe for the collection changes, but the results are looped for 1000 times , as 1000 entries in the colleciton.
Is there any way to get the whole collection entries in one single shot and mean time to subscribe the changes in the collection ?.
Yes, there are a couple of ways you can do it, mostly depending on how you want to handle the data.
If having everything at once is important, then use a Method such as:
MeteorObservable.call('getAllElements', (err, result) => {
// result.length === all elements
})
While on server side doing
Meteor.methods({
getAllElements:function(){return myCollection.find().fetch()}
})
Now, if you want to listen to changes, ofcourse you'll have to do a subscription, and if you want to lower the amount of subscriptions, use rxjs' debounceTime() function, such as (from your code):
this.theData.debounceTime(400).subscribe(value => ...., err =>)
This will wait a certain amount of time before subscribing to that collection.
Now, based on your intent: listening to changes and getting everything at once, you can combine both approaches, not the most efficient but can be effective.
As #Rager explained, observables are close to streams, so when you populate data on miniMongo (front end collection you use when you find() data and is populated when you subscribe to publications) it will start incrementing until the collection is in sync.
Since miniMongo is populated when you subscribe to a publication, and not when you query a cursor, you could either:
Try the debouceTime() approach
Use a Meteor.Method after subscribing to the publication, then sync both results, keeping the first response from the method as your starting point, and then using data from Collection.find().subscribe(collectionArray => ..., err=>) to do whatterver you want to do when changes apply (not that recommended, unless you have a specific use case for this)
Also, .zone() function is specific to force re-render on Angular's event cycle. I'd recomend not use it if you're processing the collections' data instead of rendering it on a ngFor* loop. And if you're using an ngFor* loop, use the async pipe instead ngFor="let entry of Collection | async"
I don't think that's possible. When you subscribe to an Observable it handles values as a "stream", not necessarily a loop. I have seen some makeshift helper methods that handle the data synchronously, though the time it takes to subscribe is not decreased. Check out this article for an under the hood look... A simple Observable implementation
However, you can set it up to only loop once.
The way that I've been setting up that scenario, the collection only gets looped through one time (in the constructor when the app starts) and detects changes in the collection. In your case it would look like:
values: YourModel[] = []; //this is an array of models to store the data
theData: Observable<YourModel[]>;
errors: string[];
subFinished: boolean = false;
constructor(){
this.theData = OrderDetails.find({expectedShipDate:{$in:strArr}},{fields:{"expectedShipDate":1,"loadNo":1},sort:{"expectedShipDate":1}}).zone();
MeteorObservable.subscribe('orderFilter').subscribe();
//push data onto the values array
this.theData.subscribe(
value => this.values = value,
error => this.errors.push("new error"),
() => this.subFinished = true
);
}
The "values" array is updated with whatever changes happen to the database.
I've made a function that calls on the FireBase database and will return a MutableList. However, when I try to make it return on a specific line, it says it requires a Unit instead of the MutableList.
fun firebaseCollect(key: String): MutableList<CustomList> {
var ref = FirebaseDatabase.getInstance().getReference(key)
var lessonList = mutableListOf<CustomList>()
ref.addValueEventListener(object: ValueEventListener{
override fun onCancelled(p0: DatabaseError?) {
}
override fun onDataChange(p0: DataSnapshot?) {
if (p0!!.exists()) {
lessonList.clear()
for (index in p0.children) {
val lesson = index.getValue(CustomList::class.java)
lessonList.add(lesson!!)
}
return lessonList
}
}
})
return lessonList
}
Type mismatch. Required: Unit, Found: MutableList< CustomList > is found at the first return lessonList since what I am asking for it to return is a MutableList not a Unit. I am confused as to why this happens. The last return would give an empty list. It is currently my first jab at FireBase and this is a practice I am doing. The rules for read and write have been set to public as well. How should I recode the function that I am able to return the data from FireBase into the function and passed back to the caller?
Firebase APIs are asynchronous. For your case, that means addValueEventListener returns immediately. Then, some time later, the listener you passed to it will be invoked with the data you're looking for. Your return statement in the callback doesn't actually return any data to the caller. In fact, you can't return anything from that callback. At the bottom of your function, when you return lessonList, you're actually returning an initially empty list to the caller, which may change later when the data finally arrives.
To get a better sense of how your code works, put log lines in various places, and see for yourself the order in which the code is invoked. You can read more about why Firebase APIs are asynchronous by reading this article. The bottom line is that you'll need to interact with the asynchronous APIs using asynchronous programming techniques. Don't try to make them synchronous.
Data is loaded asynchronously from Firebase. Once the data is fetched the method onDatachange() is invoked.
You are returning lessonList inside onDatachange(). Return type of onDatachange() is void(Unit in kotlin). This is the reason for the type mismatch error.
For returning the result from the method onDatachange() try this.
I have a Meteor Helper that does a GET request and am supposed to get response back and pass it back to the Template, but its now showing up the front end. When I log it to console, it shows the value corerctly, for the life of mine I can't get this to output to the actual template.
Here is my helper:
UI.registerHelper('getDistance', function(formatted_address) {
HTTP.call( 'GET', 'https://maps.googleapis.com/maps/api/distancematrix/json? units=imperial&origins=Washington,DC&destinations='+formatted_address+'&key=MYKEY', {}, function( error, response ) {
if ( error ) {
console.log( error );
} else {
var distanceMiles = response.data.rows[0].elements[0].distance.text;
console.log(response.data.rows[0].elements[0].distance.text);
return distanceMiles;
}
});
});
In my template I pass have the following:
{{getDistance formatted_address}}
Again, this works fine and shows exactly what I need in the console, but not in the template.
Any ideas what I'm doing wrong?
I posted an article on TMC recently that you may find useful for such a pattern. In that article the problem involves executing an expensive function for each item in a list. As others have pointed out, doing asynchronous calls in a helper is not good practice.
In your case, make a local collection called Distances. If you wish, you can use your document _id to align it with your collection.
const Distances = new Mongo.collection(); // only declare this on the client
Then setup a function that either lazily computes the distance or returns it immediately if it's already been computed:
function lazyDistance(formatted_address){
let doc = Distances.findOne({ formatted_address: formatted_address });
if ( doc ){
return doc.distanceMiles;
} else {
let url = 'https://maps.googleapis.com/maps/api/distancematrix/json';
url += '?units=imperial&origins=Washington,DC&key=MYKEY&destinations=';
url += formatted_address;
HTTP.call('GET',url,{},(error,response )=>{
if ( error ) {
console.log( error );
} else {
Distances.insert({
formatted_address: formatted_address,
distanceMiles: response.data.rows[0].elements[0].distance.text
});
}
});
}
});
Now you can have a helper that just returns a cached value from that local collection:
UI.registerHelper('getDistance',formatted_address=>{
return lazyDistance(formatted_address);
});
You could also do this based on an _id instead of an address string of course. There's a tacit assumption above that formatted_address is unique.
It's Meteor's reactivity that really makes this work. The first time the helper is called the distance will be null but as it gets computed asynchronously the helper will automagically update the value.
best practice is not to do an async call in a helper. think of the #each and the helper as a way for the view to simply show the results of a prior calculation, not to get started on doing the calculation. remember that a helper might be called multiple times for a single item.
instead, in the onCreated() of your template, start the work of getting the data you need and doing your calculations. store those results in a reactive var, or reactive array. then your helper should do nothing more than look up the previously calculated results. further, should that helper be called more times than you expect, you don't have to worry about all those additional async calls being made.
The result does not show up because HTTP.call is an async function.
Use a reactiveVar in your case.
Depending on how is the formated_address param updated you can trigger the getDistance with a tracker autorun.
Regs
Yann