I'm playing with Firebase as an alternative to a local Mongo store, for the time being.
I've followed various tutorials, however they are all for older versions of ES6. I've tried to tweak them to v14 and ES6 but, well, no errors but no data!
Some code:
var Rebase = require('re-base');
var base = Rebase.createClass('https://reactathon.firebaseio.com/days');
...
componentDidMount() {
console.log('ExampleComponent Mounted');
base.bindToState('days', {
context: this,
state: 'days',
asArray: true
});
console.log(this.state.days[0]);
}
The console simply logs undefined. I've tried the base URL with and without /days. I've tried getting the data as an object instead of an array. I have a feeling I'm simply pointing at the wrong thing.
Any thoughts?
Cheers.
bindToState is an asynchronous method so it's going to take some time to set up that listener. You're logging before the listener has been set up. As Jacob mentioned in his comment, move your log to your render method and then once your state is bound to Firebase your component will re render and you should see your data.
Related
I have the following event listener:
viewer.camera.moveStart.addEventListener(function(removeextra) {
// the camera started to move
clearoriginal();
});
viewer.camera.moveEnd.addEventListener(function(addback) {
// the camera stopped moving
getresults();
});
How can I remove these event listeners? I do not know the syntax.I tried with the following it does not work.
viewer.camera.moveStart.removeEventListener(removeextra);
viewer.camera.moveEnd.removeEventListener(addback);
I looked into Cesium and I think you might rewrite them like this
viewer.camera.moveStart.addEventListener(clearoriginal);
viewer.camera.moveEnd.addEventListener(getresults);
// then to remove
viewer.camera.moveStart.removeEventListener(clearoriginal);
viewer.camera.moveEnd.removeEventListener(getresults);
viewer.camera.moveEnd.removeEventListener('click',
getresults,// pass the method which you add
false
);
addEventListener() and removeEventListener() are not present in older browsers. You can work around this by inserting the following code at the beginning of your scripts, allowing the use of addEventListener() and removeEventListener() in implementations that do not natively support it. However, this method will not work on Internet Explorer 7 or earlier, since extending the Element. a prototype was not supported until Internet Explorer 8.
I have a Vue PWA and it stopped creating my IndexDB object stores on first load or upgrade. Here is my code, I am using the latest version of IDB (https://github.com/jakearchibald/idb):
await openDB('dbname', 1, {
upgrade(db, oldVersion, newVersion, transaction) {
switch (newVersion) {
case 0:
// a placeholder case so that the switch block will
// execute when the database is first created
// (oldVersion is 0)
// falls through
case 1:
db.createObjectStore('change_log', {keyPath: 'id'});
db.createObjectStore('person', {keyPath: 'id'})
.createIndex('username', 'username');
break;
}
}
});
I have tried multiple browsers and incognito tabs, etc. and the same thing always happens. The database is created, but no object stores are created. I use developer tools to clear all the data in the PWA and refresh but the same thing happens.
If I increment the version number, the version of my database gets updated in the browser, but the object stores still do not get added.
The upgrade() function does not get called.
I had this happen to me earlier in my development, and I fixed it, but I can't remember how. I feel like it may not actually be a coding issue...
OK, I found the problem. I added a logging mechanism to my App and there was code running BEFORE my upgrade code that was opening the database to create a log entry. Therefore, it was creating the database (with no object stores) before my upgrade method was being called. I changed my open database code to always include the upgrade method to solve my problems.
I am trying to get some data from firebase. Any idea how can I get the latest data (not from cache) when I have persistence enabled? I tried keepSynced; I still get stale data. Is this the correct usage?
userRef = FIRDatabase.database().reference().child("<path>")
userRef.keepSynced(true)
userRef.observeSingleEvent(of: .value, with: { snapshot in
...stale data here...
})
Or the only option is to use observe instead of observeSingleEvent? I don't like the fact that with observe I get the cache data first, and then the event triggers a second time with data from the server. So with observe, when I navigate to this screen, first I see a blank table, then I see the table with stale data, and then I see the table with latest data.
Thanks.
EDIT:
https://stackoverflow.com/a/34487195/1373592 -
This post says keeySynced should work. But it's not working for me. I would like to know if I am doing something wrong.
I retrieve some explanation, I think it might help you in your case :
ObserveSingleEventType with keepSycned will not work if the Firebase
connection cannot be established on time. This is especially true
during appLaunch or in the appDelegate where there is a delay in the
Firebase connection and the cached result is given instead. It will
also not work at times if persistence is enabled and
observeSingleEvent might give the cached data first. In situations
like these, a continuous ObserveEventType is preferred and should be
used if you absolutely need fresh data.
I think you don't have the choice to use a continuous listener. But to avoid performance issues why you don't remove yourself your listeners when you don't it anymore.
Here is an example on how to ALWAYS get latest data from firebase when persistence is turned on. Use observe event, keepSynced on your ref and terminate listener if you don't want to keep it always. After several trials, I came up with this and it is working.
func readFromFB() {
let refHandle: DatabaseHandle?
let ref: DatabaseReference? = firebase.child(nodeName)
ref?.keepSynced(true)
refHandle = ref!.observe(.value, with:
{ snapshot in
if snapshot.exists() {
for item in ((snapshot.value as! NSDictionary).allValues as Array) {
//do whatever tasks
}
}
})
if let rf = ref {
rf.removeObserver(withHandle: refHandle!)
}
}
I have such a method in my Meteor app:
addLocation: (location, tid) => {
location = LocationSchema.clean(location);
LocationSchema.validate(location);
var lid = Locations.insert(location);
Thoughts.update({_id: tid}, {$push: {locations: lid}});
}
I subscribe both Locations and Thoughts collections. But unfortunately after calling my method only changes in Locations collection are visible - my modified thought is still the same and I must reload page to see its changes. Is it bug in Meteor or my mistake? Do you know some ways to solve or bypass this problem?
What's more, when I push some value to locations array in some thought with Robomongo, changes are visible though. It looks like the problem is that two changes try to be seen at the same time.
[I am new to ADO.NET and the Entity Framework, so forgive me if this questions seems odd.]
In my WPF application a user can switch between different databases at run time. When they do this I want to be able to do a quick check that the database is still available. What I have easily available is the ObjectContext. The test I am preforming is getting the count on the total records of a very small table and if it returns results then it passed, if I get an exception then it fails. I don't like this test, it seemed the easiest to do with the ObjectContext.
I have tried setting the connection timeout it in the connection string and on the ObjectConntext and either seem to change anything for the first scenario, while the second one is already fast so it isn't noticeable if it changes anything.
Scenario One
If the connect was down when before first access it takes about 30 seconds before it gives me the exception that the underlying provider failed.
Scenario Two
If the database was up when I started the application and I access it, and then the connect drops while using the test is quick and returns almost instantly.
I want the first scenario described to be as quick as the second one.
Please let me know how best to resolve this, and if there is a better way to test the connectivity to a DB quickly please advise.
There really is no easy or quick way to resolve this. The ConnectionTimeout value is getting ignored with the Entity Framework. The solution I used is creating a method that checks if a context is valid by passing in the location you which to validate and then it getting the count from a known very small table. If this throws an exception the context is not valid otherwise it is. Here is some sample code showing this.
public bool IsContextValid(SomeDbLocation location)
{
bool isValid = false;
try
{
context = GetContext(location);
context.SomeSmallTable.Count();
isValid = true;
}
catch
{
isValid = false;
}
return isValid;
}
You may need to use context.Database.Connection.Open()