I currently have an app with about 200 users and I'm trying to restructure my firebase db without breaking functionality so I can expand to other schools. I plan on pushing a required update before doing so.
Right now my database looks something like this
/users/user
/otherproperty/object
I am trying to move everything under one big "school" folder so it looks like this.
school/users/user
school/otherproperty/object
Is there a way I can change my firebase to look like this?
You could implement Firebase realtime database triggers that would fire whenever any data is added/modified/deleted under the old data hierarchy that performed the same updates in the new data hierarchy. You could also implement triggers that performed the same updates from the new hierarchy into the old hierarchy.
Then, you can migrate users from the old hierarchy into the new one at whatever rate/schedule makes the most sense to you. The triggers would maintain data consistency between the two hierarchies.
Once all users are migrated to the new hierarchy, you can remove the triggers and move forward with only the new hierarchy.
The easiest thing to do with a relatively small amount of data is write a script to get a snapshot of the data and set it in the new path.
let userRef = firebase.database().ref('users')
let newUserRef = firebase.database().ref('MYSCHOOL/users')
userRef.on('value', function(usersSnapshot) {
newUserRef.set(usersSnapshot.val())
});
You can also use the REST API and use shallow queries to grab the individual keys and query data in smaller chunks.
Related
Firebase allows having multiple projects in a single application.
// Initialize another app with a different config
var secondary = firebase.initializeApp(secondaryAppConfig, "secondary");
// Retrieve the database.
var secondaryDatabase = secondary.database();
Example:
Project 1 has my users collection; Project 2 has my friends collection (suppose there's a reason for that). When I add a new friend in the Project 2 database, I want to increment the friendsCount in the user document in Project 1. For this reason, I want to create a transaction/batch write to insure consistency in the data.
How can I achieve this? Can I create a transaction or a batch write between different Firestore instances?
No, you cannot use the database transaction feature across multiple databases.
If absolutely required, I'd probably instead create a custom locking feature. From wiki,
To allow several users to edit a database table at the same time and also prevent inconsistencies created by unrestricted access, a single record can be locked when retrieved for editing or updating. Anyone attempting to retrieve the same record for editing is denied write access because of the lock (although, depending on the implementation, they may be able to view the record without editing it). Once the record is saved or edits are canceled, the lock is released. Records can never be saved so as to overwrite other changes, preserving data integrity.
In database management theory, locking is used to implement isolation among multiple database users. This is the "I" in the acronym ACID.
Source: https://en.wikipedia.org/wiki/Record_locking
It's been three years since the question, I know, but since I needed the same thing I found a working solution to perform the double (or even ^n) transaction. You have to nest the transactions like this.
db1.runTransaction(t1 => db2.runTransaction(t2 => async () => {
await t1.set(.....
await t2.update(.....
etc....
})).then(...).catch(...)
Since the error is propagated in the nested promises it is safe to execute the double transaction in this way because for a failure in any one of the databases it results in the error in all of them.
I am building a chat engine using firebase in unity. I want to differentiate between the existing data and all the new data that gets added into the database. There is method once in web sdk of firebase which helps in differentiating between old and new data, is anyone aware if we have something similar on unity
There is no direct way to do this, one way that is a workaround is to add a timestamp value in all the entries maintained in the database and each time one subscribes for the new data we make use of the OrderByValue|OrderByKey and StartAt to do the same.
In the beginning value for StartAt will be 0 but post that whenever a child gets added we can update the StartAt value to that so that the next time client subscribes for the childAdded, it will only receive data post the last child.
I've read almost everywhere about structuring one's Firebase Database for efficient querying, but I am still a little confused between two alternatives that I have.
For example, let's say I want to get all of a user's "maxBenchPressSessions" from the past 7 days or so.
I'm stuck between picking between these two structures:
In the first array, I use the user's id as an attribute to index on whether true or false. In the second, I use userId as the attribute NAME whose value would be the user's id.
Is one faster than the other, or would they be indexed a relatively same manner? I kind of new to database design, so I want to make sure that I'm following correct practices.
PROGRESS
I have come up with a solution that will both flatten my database AND allow me to add a ListenerForSingleValueEvent using orderBy ONLY once, but only when I want to check if a user has a session saved for a specific day.
I can have each maxBenchPressSession object have a key in the format of userId_dateString. However, if I want to get all the user's sessions from the last 7 days, I don't know how to do it in one query.
Any ideas?
I recommend to watch the video. It is told about the structuring of the data very well.
References to the playlist on the firebase 3
Firebase 3.0: Data Modelling
Firebase 3.0: Node Client
As I understand the principle firebase to use it effectively. Should be as small as possible to query the data and it does not matter how many requests.
But you will approach such a request. We'll have to add another field to the database "negativeDate".
This field allows you to get the last seven entries. Here's a video -
https://www.youtube.com/watch?v=nMR_JPfL4qg&feature=youtu.be&t=4m36s
.limitToLast(7) - 7 entries
.orderByChild('negativeDate') - sort by date
Example of a request:
const ref = firebase.database().ref('maxBenchPressSession');
ref.orderByChild('negativeDate').limitToLast(7).on('value', function(snap){ })
Then add the user, and it puts all of its sessions.
const ref = firebase.database().ref('maxBenchPressSession/' + userId);
ref.orderByChild('negativeDate').limitToLast(7).on('value', function(snap){ })
I'm learning angularjs, firebase, angularfire by building a sample app. It's a dictionary app that any one can add a word, add several explanation to the word, add several common usage to the word, add example centences to the word. People can freely add new word via this web app. OR people can freely realtime search a word and display the content of that word. When I build the app.
I found everytime when I search a word, I have to load all the data and then check if the query string exist in the data and then display the content if exist. So, it's quite heavy if the library become very big.
How can I query a string if it exist from the server side and if exist, just download that piece of data?
Here is a very simple example that is on the firebase site (Retreiving data). I suggest you take a look at that page, there is a lot more info there about this subject. Now the example:
var ref = new Firebase("https://dinosaur-facts.firebaseio.com/dinosaurs");
ref.orderByChild([the child node to compare to]).equalTo([what you are searching]).on("child_added", function(snapshot) {
//do something with the data in snapshot
});
I want to use angularfirecollection to keep one-way sync with a list of data. The structure is a list of 'things' with various properties (e.g. 'Likes') and users who each hold a subset of 'things' keys (e.g. -jsdzsdrestofkey: true). U
sing angularfirecollection (or firebase native 'on'), I can sync up all things that a particular user has... I can also grab (using firebase native 'once') each 'thing''s properties to display.
In angular, however, I need to use $apply() to inject the property data into scope for each item in the user's 'thing' list. To keep things in sync, I suppose I can use firebase's on change event... But this all requires me to create new references for each thing in a user's list.
What is the best way to approach grabbing relational data in firebase, while keeping both the list and the relational data in sync?
Thanks!
Irfaan
If I understand correctly, it sounds like you should use FirebaseIndex and feed the index directly into an angularFireCollection. Then you wouldn't need to use $apply since the thing data will already be in the $scope, and everything will stay synced:
var index = new FirebaseIndex(fb.child('users/789/thing_list'), fb.child('things'));
$scope.things = angularFireCollection(index);
// $scope.things will contain the user's things with the associated thing data