I'm trying to delete a specific value from a firebase realtime database, but I don't know how to do it because I don't know to save or find the key value of the child which is automatically generate.
If you see the picture I've only managed to remove all the children from the first key with
FirebaseDatabase.getInstance().reference.child("Comentarios").removeValue()
But I need to delete just by the child creadoPor
Is there any way of skkiping an unnamed child?
FirebaseDatabase.getInstance().reference.child("Comentarios").removeValue()
But I need to delete just by the child creadoPor.
Since you know the "grantparent" key of the data and the value of one of the nodes properties, you can use a query to find the nodes that match that value.
FirebaseDatabase.instance
.ref("Comentarios")
.child("-NGi7xP...")
.orderByChild("creadoPor")
.equalTo("R7lji3...")
When you get the DataSnapshot from the query, you'll need to loop over its children as shown in the documentation on listening for value events. Even when there's only one result, you'll get a list of one child node and thus will need to loop over them.
Related
This is my firebase realtime database structure
I want to retrieve all questions with QID = "PQ1" . What i tried is given below . Its result is null .
database.child("Question").child("QID").equalTo("PQ1").limitToFirst(200).get().addOnSuccessListener {
Log.i("12345", "Got value ${it.value}")
}
My references :
Firebase - Search a child by value
Firebase search by child value
Search firebase by Child of child value
Your call to database.child("Question").child("QID") looks for a child node at path /Question/QID in your database, which doesn't exist and thus explains why you get an empty snapshot.
To query the Firebase Realtime Database needs two steps:
You order all child nodes on a property, on their key, or on their value by calling on of the orderBy... methods.
You then filter the ordered child nodes by calling one or more of the equalTo, startAt, startAfter, endAt, endBefore, limitToFirst and/or limitToLast methods.
While you're doing #2, you're not ordering the nodes first by calling orderBy....
The correct code:
database.child("Question").orderByChild("QID").equalTo("PQ1").limitToFirst(200).get().addOnSuccessListener {
Log.i("12345", "Got value ${it.value}")
}
Also don't forget that executing a query will potentially have multiple results, so the snapshot in it.value contains a list of those results and you will need to iterate over its children. Even if there is only a single result, the snapshot will contain a list of one result.
I am trying to achieve a scenario where firebase triggers only once when a collection is created and not every time that a document is added to the collection. Let's say I want it to trigger only for the first document added to the collection and not for every other document added to the same collection. How can that be done? Please help !!!
There is no such trigger for Cloud Functions. Your trigger path must specify exactly one document, or use wildcards to specify a path that could possibly match many documents.
If you want to know what a collection contains its first document, you will have to either:
Maintain a count of documents in that collection (perhaps in yet another document in another collection), and trigger of the change of that value when it goes from 0 to 1.
Query all of the documents in the collection where a document was just created in order to figure out if it was the first one.
Both of these requires a fair amount of extra code - very much not trivial to implement correctly for arbitrary collections. They could also run into problems under heavy load. If these options won't work for you, I suggest figuring out another way to get you function to trigger at the right time.
While It's not possible to do directly. You can check if collection contains any elements, and if it does it means that it exists.
const result =await firestore.collection("collection").limit(1).get()
if(result.size){
// Collection exists
}
I stored an Array as a FieldValue in one of my document in Firestore. Now I want to update one of its element value. As per the documentation I can use arrayRemove or arrayUnion function to remove the element from array but I didn't see any method to update the value of element. Is there any way that I can help me to update the elements' value.
Here I stored array in "patients" field of document. This array represents list of patients. Look at 0th position of element. Here status's value is "current". I want to update this to "processed". Is there anyway that I can do so.
Also is there any way that I can query the elements of array on the basis of the value placed on status key.
As per the documentation I can use arrayRemove or arrayUnion function to remove the element from an array.
There is no way you can use one of those functions to add or remove elements from an array that contains objects. To be able to use those functions, your array should contain for example literal strings. In that way, you can add or remove one of the elements using arrayRemove() or arrayUnion() functions.
I didn't see any method to update the value of an element.
There is no update method. arrayUnion() method will add a new element in the array only if it does not exist. If you want to update an element, you have to remove it first from the array and then add the new one. This is also available in the case of strings and not in the case of objects.
Is there any way that I can help me to update the elements' value.
Yes, two ways in which you can achieve this. The first one would be to get the entire document, get the patients property as a list of hashmaps, iterate through its elements, make the desired changes and write the document back. The second one would be to transform that array into a subcollection where each patient will become a document. In this way, you can simply update add or remove a document using the corresponding functions.
Also is there any way that I can query the elements of the array on the basis of the value placed on the status key.
Using your current document structure, no. If you want to query the patients of a user based on the value of a specific property, you should definitely use the second approach. There is no way you can achieve this using your actual schema.
I am using Firebase to store data. When I delete all data within a single parent node, the parent node also gets deleted. A parent node exists only if there is at least a single value of data in it.
How do I modify the rules in such a way that the parent node always exists even if there is not a single value in it. (I set the values of .read and .write in the rules to true.)
In the above image, the parent 'Queue Members' has a value 'hello'. If I delete 'hello', the parent 'Queue Members' also gets deleted.
There is no way to have a node without a value under it.
The Firebase Database automatically creates nodes as values are added under them. It also automatically deletes nodes when no value exists under them anymore.
This should typically not lead to any problems in your code, since requesting the value of a non-existing node leads to an empty snapshot. If you're having a problem with this in your code, it would be useful to see how you're trying to deal with it.
So I am writing a chat application that I want to have multiple rooms, however, I can't find a button on the Firebase console that I can add child collections.
I've tried exporting, editing, then importing but that doesn't seem to do much. I have looked at some Firebase tutorial's but I can't find one that explains this.
Anything you enter in the console has to have a value itself, or at least one child (with a value). This is because Firebase does not explicitly store "null" or empty values in the database. You can enter the name of the collection and then rather than a value use the + button at the right to start adding children to it and so on until you reach a node with a value:
You cannot however simply create a placeholder for a collection that has no values. If you need a collection but can't initialize any of its data, just use your security rules to define what's allowed and write your client code knowing it may or may not exist. Firebase allows you to attach listeners to nodes that don't exist yet.