When trying to pull data from a MySQL database, I can do something like:
SELECT * FROM users ORDER BY id WHERE vehicle = car
That should get me all the users that drives a car and not show users that drives a motorcycle for instance.
Is there something like this for Firebase? I can only retrieve specific data from one user?
My firebase database is like this: user -> user info (name, age, vehicle etc..)
I want to query every user that drives a car and display them in a row. How do I do that?
I have tried the following, but I didn't succeed with what I tried to do, since after users the users id is the next child. Is there a way to query past that?
var recents = firebase.database().child('users').orderByChild('department').equalTo(department);
recents.on('child_added', function(snapshot) {
var countOfUserInDepartment = snapshot.count;
document.querySelector("#cphCount").innerHTML = countOfUserInDepartment;
});
There are no count queries (nor other aggregation queries) in the Firebase Database. Your options are:
Retrieve all data matching your query and count client-side
Keep a separate count-node that you update whenever you add/remove items.
For #2 you may find it convenient to use Cloud Functions, for which there an an example of keeping such a counter.
Also see:
Firebase count group by
Database-style Queries with Firebase
In Firebase, is there a way to get the number of children of a node without loading all the node data?
How to get size of an element/list in Firebase without get it all?
Related
I have deployed an app with React and I am using Firebase Realtime database to store some info about attention tickets in a call center. The database will store aprox 80 tickets info per day, but this is cumulative. I want to avoid this so I will not reach the firebase storage limit.
My idea so far is to delete every day at noon the tickets from the database, so It will only store the data from the current date and eliminate it at noon.
I am using remove() function from firebase, but when I tried referencing to the collection, It was entired deleted, I just want to delete the documents but not the entire collection.
Is there a way to specify Firebase to delete docs only, maybe to delete every docs except one?
This is the bunch of code that I pretend to use for deleting (Based on JS)
function deletedata(){
const dbRef = query(ref(db,'/mycollectionpath'));
onValue(dbRef, (snapshot)=>{
snapshot.forEach(childSnapshot=>{
let keyName = childSnapshot.key;
remove(dbRef);
})
});
}
setInterval(deletedata,1000)
The Firebase Realtime Database automatically creates parent nodes when you write a value under them, and it automatically deletes parent nodes when there are no longer any values under them. There is no way to have a node without a value.
If you want to keep the node, consider writing a dummy value. For example, this would remove all child nodes from mycollectionpath and replace them with a single true value:
const dbRef = ref(db, '/mycollectionpath');
dbRef.set(true);
I've been looking for this but i have no idea about the name of this.
I am creating a data model on MySql and i have a table called users and i want to restrict the queries from each user, for example, allow to read all the rows from the clients table or only allow them to query some selected clients. It's like a filter but my question is, how can i save the name of the clients for each users or allow them to have access to all the clients?
My first idea was create a Many to Many relationship but when i create a new client i need to update the table for each user that have the options to query all the clients.
My second idea was create a table with a column called selectedClients with array data type and save ["all"] and whith an "if" make the query and if i selected various clients, in that filed will be save the id of the clients such as ["clientID1", "clientID2"] and after, in my middleware i will query the table only with the id's of that field. But the problem is that it's not a good practice i think and when deleted a client, i need to deleted for each field of that id.
How can i implement this?
Database-wise, what you want is a many-to-many relationship. Many users can access many clients. So you'll have a users table, a clients table, and a usersclients table (or whatever you want to name it). The usersclients table would map users.id (presuming id is the name of the primary key) to clients.id. There would be 1 row in usersclients for every client that every user can access.
As for users that can view all clients, my initial thought is to have that set as a flag on the user. Then, when you're building the list of clients, do something like:
(pseudo-code, please excuse any c# influence)
let viewableClients = [];
if( user.canViewAllClients ) {
clients = queryToGetAllClients();
} else {
clients = user.UserClients.forEach(uc => uc.Client);
}
I have many to many relational data model. For example , i have a chat room and it has many users.
{Chatroom:
ChatRoomID:ID,
Somedata...
User:{
ID:userid,
Somedata...
}
}
I have a user object and i need to filtre those by user.
DataStore.query(ChatRoom,e=>e.User.Id("eq",myID))
I tried to query the data which has my userid then get the ChatRoomID. But i didnt work as expected. I can filter it with its main keys but i cant go through inside the object to filter. Currently i am doing this the same as the aws document. Which is-->
DataStore.query(ChatRoom).filter(e=> e.user.id==myID)
My concern is ,is this query above gets the whole data to filter ? For the first one, it looks like it getting the filtered data like select queries as we do in SQL. But i m worried about using second one. What if i have 100.000 rooms and 500.000 users inside it ? Is it get the whole data before filtering with a JavaScript functions like filter, map etc. ? I dont get the logic behind.
I am working on firebase for the first time. I am confused in querying the database. I have two objects on the database, one is the Auth and second one is the Chats. In Auths I have number of UID(user id) nodes, each of these nodes have their respective username. What I am trying to do is, I want to query that Auth object and get all the usernames which is equal to the one I take from a user through input box. In my sql it will be simple as SELECT * FROM auth WHERE username = userInputValue. I need same query like this, Below is what I have done so far.
var _firbaseDB = firebase.database(),
_firebaseAuthRef = _firbaseDB.ref("Auth/");
$("body").on("submit",".search-from",function(e){
e.preventDefault();
var ev = e.target,
_allUsers = $(ev).serializeArray()
_user = _allUsers[0].value;
_firebaseAuthRef.equalTo(_user).on("child_added",function(res){
console.log(res.val());
})
})
You were almost there. What's missing is that you need to specify which attribute you're querying on:
_firebaseAuthRef.orderByChild("n").equalTo(_user).on("child_added",function(res){
console.log(res.val());
})
More info on the Firebase Database Documentation.
I'm having trouble trying to figure out how to get a list to query as desired. Full disclosure, it may not be possible and if that's the case then at least it will provide me with some closure. I want to query a friend's list based on presence, where friends who are active are queried on top.
Here is my database structure:
friendships
$UID
$UID: true
users
$UID
active:true/false
I need the list to stay synced so I need to use .on('value'). I've tried a couple different methods using child_added as well as iterating through a snapshot using snapshot.forEach() and pushing the childSnapshot key:value pairs into an array so I could then use lodash to order the list via the active key on the client side, but ran into the issue of it pushing a "new" item into the array for each active value change so there would be multiple items for any given user.
Any help or insight would be appreciated, spent the majority of yesterday attempting to figure this out before resorting back to an unorganized list using the following code:
const {currentUser} = firebase.auth();
firebase.database().ref(`/friendships/${currentUser.uid}`).on('value, snapshot => { //redux dispatch action, payload: snapshot.val() })
There's no great solution for this. Firebase doesn't have any sort of join or join query, so you could do usersRef.orderByChild('active').equalTo(true), but that will just return you all active users. You'll need to do separate queries to pull in their friendships.