Is it possible to retrieve data nodes that meet a specific condition using the Firebase JavaScript API in a single trigger? And does it establish a new TCP connection for every query?

Question

Is it possible to retrieve data nodes that meet a specific condition using the Firebase JavaScript API in a single trigger? And does it establish a new TCP connection for every query?

Looking for a solution using the Firebase JavaScript API, not the REST method like in this question. My query is a bit different, so I'm hoping for a unique solution. I'm trying to run a query similar to this:

"SELECT * FROM db.table WHERE field1 ="val1";"

With Firebase, we can achieve this with the following code:

var ref = new Firebase("https://db.firebaseio.com/table");
ref.orderByChild("field1").equalTo("val1").on("value", function(record) {
  console.log(record.val())
});

When using Firebase, does each child query for field1="val1" open a new TCP connection? And is there a way to retrieve all the children that meet the condition in a single callback (i.e., trigger the callback once when all data is downloaded at the client)?

javascript firebase firebase-realtime-database

Answer 1

Answer №1

My callback function in Firebase is triggered for every child that meets the condition field1="val1"

Actually, the callback function is triggered only once, and all the matching nodes are passed in the DataSnapshot parameter. To access each matching node, you can iterate over them using the following code:

var ref = new Firebase("https://db.firebaseio.com/table");
ref.orderByChild("field1").equalTo("val1").on("value", function(snapshot) {
  snapshot.forEach(function(record) {
    console.log(record.val())
  });
});

Even if there is only one child, the loop is necessary. You can use snapshot.numChildren() to check if there are any nodes matching your query.

Does each child query open a new TCP connection?

No, the Firebase client establishes a WebSocket connection when you first initialize new Firebase(...). All communication thereafter happens over this WebSocket. Only in environments that don't support WebSockets does Firebase resort to HTTP long-polling. You can view the network tab in your browser's debugger to see the network activity.

Is there a way to retrieve all matching children in a single callback once they are all downloaded at the client?

I believe I addressed that question previously.

Update based on the comments

Are the callback functions passed to forEach called synchronously?

Yes

Answer 2

My callback function in Firebase is triggered for every child that meets the condition field1="val1"

Actually, the callback function is triggered only once, and all the matching nodes are passed in the DataSnapshot parameter. To access each matching node, you can iterate over them using the following code:

var ref = new Firebase("https://db.firebaseio.com/table");
ref.orderByChild("field1").equalTo("val1").on("value", function(snapshot) {
  snapshot.forEach(function(record) {
    console.log(record.val())
  });
});

Even if there is only one child, the loop is necessary. You can use snapshot.numChildren() to check if there are any nodes matching your query.

Does each child query open a new TCP connection?

No, the Firebase client establishes a WebSocket connection when you first initialize new Firebase(...). All communication thereafter happens over this WebSocket. Only in environments that don't support WebSockets does Firebase resort to HTTP long-polling. You can view the network tab in your browser's debugger to see the network activity.

Is there a way to retrieve all matching children in a single callback once they are all downloaded at the client?

I believe I addressed that question previously.

Update based on the comments

Are the callback functions passed to forEach called synchronously?

Yes

Is it possible to retrieve data nodes that meet a specific condition using the Firebase JavaScript API in a single trigger? And does it establish a new TCP connection for every query?

Answer №1

Update based on the comments

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