I am just starting out with Firebase and have managed to send data to a Firebase Realtime Database. The problem is that some times it works and sometimes not. I am struggling to understand why.
Here is a code snippet
var pq_data = jsPsych.data.get().values();
for (var ix= 0; ix < pq_data.length; ix++){
var object=pq_data[ix];
var pq_boo = pq_database.ref(subj_id +ix.toString()+'/').update(object)
}
As I say this works sometimes but not always and I understand that it may have something to do with the code completing before the write operations have(?)
I have read but do not clearly understand advice about onCompletion and I am still in the dark. I need to make sure each object is written to the database - is this possible and if so how?
Very much a beginner,
Philip.
// Import Admin SDK
var admin = require("firebase-admin");
// Get a database reference to our blog
var db = admin.database();
var ref = db.ref("server/saving-data/fireblog");
First, create a database reference to your user data. Then use set() / setValue() to save a user object to the database with the user's username, full name, and birthday. You can pass set a string, number, boolean, null, array or any JSON object. Passing null will remove the data at the specified location. In this case you'll pass it an object:
var usersRef = ref.child("users");
usersRef.set({
alanisawesome: {
date_of_birth: "June 23, 1912",
full_name: "Alan Turing"
},
gracehop: {
date_of_birth: "December 9, 1906",
full_name: "Grace Hopper"
}
});
Thanks for this Yes For brevity I didn't show all the code and so I have access to the database. The problem is with sending data to it. Sometimes it works and sometimes not.
I now realise this is related to my failure to deal with Promises. I have now some understanding of these but still need to make sure that the data gets captured in the database. SO even though the Promise may return an Error I still need to re-send the data so that it will get written to the database. Still not sure whether this is advisable or even possible.
Related
With Firestore, I add a timestamp field like this
var ref: DocumentReference? = nil
ref = Firestore.firestore()
.collection("something")
.addDocument(data: [
"name": name,
"words": words,
"created": Timestamp(date: Date())
]) { ...
let theNewId = ref!.documentID
...
}
That's fine and works great, but it's not really correct. Should be using the "server timestamp" which Firestore supplies.
Please note this is on iOS (Swift) and Firestore, not Firebase.
What is the syntax to get a server timestamp?
The syntax you're looking for is:
"created": FieldValue.serverTimestamp()
This creates a token which itself has no date value. The value is assigned by the server when the write is actually written to the database, which could be much later if there are network issues, so keep that in mind.
Also keep in mind that because they are tokens, they can present different values when you read them, to which we can configure how they should be interpreted:
doc.get("created", serverTimestampBehavior: .none)
doc.get("created", serverTimestampBehavior: .previous)
doc.get("created", serverTimestampBehavior: .estimate)
none will give you a nil value if the value hasn't yet been set by the server. For example, if you're writing a document that relies on latency-compensated returns, you'll get nil on that latency-compensated return until the server eventually executes the write.
previous will give you any previous values, if they exist.
estimate will give you a value, but it will be an estimate of what the value is likely to be. For example, if you're writing a document that relies on a latency-compensated returns, estimate will give you a date value on that latency-compensated return even though the server has yet to execute the write and set its value.
It is for these reasons that dealing with Firestore's timestamps may require handling more returns by your snapshot listeners (to update tokens). A Swift alternative to these tokens is the Unix timestamp:
extension Date {
var unixTimestamp: Int {
return Int(self.timeIntervalSince1970 * 1_000) // millisecond precision
}
}
"created": Date().unixTimestamp
This is definitely the best explanation of how the timestamps work (written by the same Doug Stevenson who actually posted an answer): https://medium.com/firebase-developers/the-secrets-of-firestore-fieldvalue-servertimestamp-revealed-29dd7a38a82b
If you want a server timestamp for a field's value, use FieldValue.serverTimestamp(). This will return a token value that gets interpreted on the server after the write completes.
So imagine the following scenario, using the Parse platform on iOS:
I get a PFObject from the server, let's call it GlassChalice.
Someone else, let's say Bill Blofeld, changes GlassChalice from a different location.
Later, I make some changes to my local GlassChalice, but don't save them to the server.
Still later, I want to update GlassChalice, but I want to update it to the current server values, in other word Bill Blofeld's values. I do not want to replace the server values with my local values, and also do not want to reset my local values to the values GlassChalice was loaded with.
So if I use revert(), will I get what I want?
According to the Parse docs:
- revert Clears any changes to this object made since the last call to save and sets it back to the server state.
...but, as in my example, clearing "changes made since the last call to save" and setting it "back to the server state" aren't always the same thing.
So far this seems like the only way to guarantee the results I want, but it has one obvious problem:
public func updateObjectFromServer(_ objectToUpdate: PFObject, then doThis: (()->Void)? = nil) {
let query = PFObject.query()
query?.whereKey("objectId", equalTo: objectToUpdate.objectId!)
query?.getFirstObjectInBackground (block: {
(serverObject, error) in
if error.isNil() {
objectToUpdate["numberOfLimbs"] = serverObject?["numberOfLimbs"]
objectToUpdate["eyePlacement"] = serverObject?["eyePlacement"]
objectToUpdate["crossStitchingTalentRating"] = serverObject?["crossStitchingTalentRating"]
objectToUpdate["clamsEaten"] = serverObject?["clamsEaten"]
} else {
//handle error...
}
doThis?()
})
}
But the huge problem here is that I have to know all the key names, and type them in explicitly, for this to work.
Is there a better, more generic, way?
I've found a ton of information on LocalStorage with HTML5 but they all focus on persistent single entries being saved.
I need to be able to have a contact form (simple name/email/phone) that gets saved to the iPad and then allows another person to submit an entry to save to the iPad locally (no Wifi/Internet available).
Then I want to be able to go in later and grab all the entries that were made in whatever format available.
Any direction & help would be appreciated.
I searched on Stackoverflow & Google but still couldn't find multiple entry tutorials or examples.
Thanks!
localStorage is a good fit for what you're after. As localStorage only supports strings, you will need to do some conversions to/from JSON to serialize the entries.
Here is some general code to hopefully get you started:
// read out any previous contact forms (initialise if it is empty)
var jsonEntries = localStorage["contactFormEntries"];
var contactFormEntries = JSON.parse(jsonEntries ? jsonEntries : '[]');
// ...
// sometime later... create a contact form record
var contactForm = {
'name': 'Timmy',
'email': 'timmy#example.com'
};
// add it to the entries array
contactFormEntries.push(contactForm);
// serialize all the contact form entries into local storage
localStorage["contactFormEntries"] = JSON.stringify(contactFormEntries);
// ...
// then, when you want to send the entries, read them all out again
var contactFormEntries = JSON.parse(localStorage["contactFormEntries"]);
Hopefully, a simple question and must have a simple answer but i have wasted almost 3hrs in getting out of this issue.
I have a user model. I want to load the first user from DB and show it on first page load.
What i am trying to use is:
in my ArrayController,
init: function(){
var user = App.User.find(1)
console.log(user);
this.set('defualtUser',user.get('name'))
}
But i cant get the name of user.
Here is the output of user in console, which indicates that data is being loaded but i can't just get it to use.
Class
__ember1367188634172: "ember270"
__ember1367188634172_meta: Meta
_changesToSync: Object
_data: Object
attributes: Object
***name: "Cafe Alpino"***
__proto__: Object
belongsTo: Object
hasMany: Object
id: null
__proto__: Object
See the name: "Cafe Alpino", i just want to display this name.
Any help???
BTW, i am a newbie with EmberJS
I think the problem here is asynchronousy. This line: var user = App.User.find(1) will result in a user record that is not loaded yet; its properties aren't set until the AJAX call returns in the background. Therefore, user.get('name') will be empty.
There are probably a few ways to solve this. I haven't used Ember Data too much (since it's not very solid at the moment), but according to the docmentation, there should be a didLoad event that you can use:
init: function() {
var user = App.User.find(1);
var _this = this;
user.on('didLoad', function() {
_this.set('defaultUser', user.get('name'));
});
}
Give it a try! Let me know if it doesn't work out.
I want to use the following method to flag people in the Person table so that they can be processed. These people must be flagged as "In Process" so that other threads do not operate on the same rows.
In SQL Management Studio the query works as expected. When I call the method in my application I receive the row for the person but with the old status.
Status is one of many navigation properties off of Person and when this query returns it is the only property returned as a proxy object.
// This is how I'm calling it (obvious, I know)
var result = PersonLogic.GetPeopleWaitingInLine(100);
// And Here is my method.
public IList<Person> GetPeopleWaitingInLine(int count)
{
const string query =
#"UPDATE top(#count) PERSON
SET PERSON_STATUS_ID = #inProcessStatusId
OUTPUT INSERTED.PERSON_ID,
INSERTED.STATUS_ID
FROM PERSON
WHERE PERSON_STATUS_ID = #queuedStatusId";
var queuedStatusId = StatusLogic.GetStatus("Queued").Id;
var inProcessStatusId = StatusLogic.GetStatus("In Process").Id;
return Context.People.SqlQuery(query,
new SqlParameter("count", count),
new SqlParameter("queuedStateId", queuedStateId),
new SqlParameter("inProcessStateId", inProcessStateId)
}
// update | if I refresh the result set then I get the correct results
// but I'm not sure about this solution since it will require 2 DB calls
Context.ObjectContext().Refresh(RefreshMode.StoreWins, results);
I know it is an old question but this could help somebody.
It seems you are using a global Context for your query, EF is designed to retain cache info, if you allways need fresh data must use a fresh context to retrieve it. as this:
using (var tmpContext = new Contex())
{
// your query here
}
This create the context and recycle it. This means no cache was stored and next time it gets fresh data from database not from cache.