How Can I Retrieve a List of Subcollection Names in Cloud Firestore?

Accessing Subcollection Names in Cloud Firestore

Listing subcollections in a document is a common requirement for organizing and navigating data stored in Cloud Firestore's hierarchical structure. However, in the client SDKs (including Web, iOS, and Android), retrieving a complete list of subcollections is not supported directly.

Client-Side Limitations:

As specified in the official documentation, "retrieving a list of collections is not possible with the mobile/web client libraries." This design choice aims to enhance security by restricting access to subcollection names, primarily for administrative tasks performed in trusted server environments.

In the client SDKs, accessing a document only returns the field names and values, excluding any subcollection names. For instance, the following code snippet will only log the field names, but not the subcollection names:

rootRef.doc('aDocument').get()
  .then(doc => {

    // only logs [ "someField", "anotherField" ], no collections
    console.log( Object.keys(doc.data()) )
  })

Server-Side Solution:

However, in server-side SDKs, such as Node.js, accessing subcollection names is supported. For Node.js, the ListCollectionIds method offers a way to retrieve the names of subcollections in a document.

var firestore = require('firestore.v1beta1');

var client = firestore.v1beta1({
  // optional auth parameters.
});

// Iterate over all elements.
var formattedParent = client.anyPathPath("[PROJECT]", "[DATABASE]", "[DOCUMENT]", "[ANY_PATH]");

client.listCollectionIds({parent: formattedParent}).then(function(responses) {
    var resources = responses[0];
    for (var i = 0; i < resources.length; ++i) {
        // doThingsWith(resources[i])
    }
})
.catch(function(err) {
    console.error(err);
});

This method returns an array of strings representing the names of the subcollections within the specified document.

Alternative Approach:

If direct access to subcollection names is crucial in a client-side environment, consider restructuring your data such that subcollection names can be inferred or derived logically from the document structure. This approach allows you to work around the limitation gracefully.

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