I have a firestore collection with a bunch of documents, each with plenty subfields. On a web page I need a list of a specific subfields from each document. Currently I load the the entire database when you load the page and then loop through and get the wanted values. This uses way to many reads to get very little data.

Is there a way to solve this e.g. a autogenerated a collection that contains field from other collection in an array or something.

Many thanks in advance

CodePudding user response：

Auto-creating such a subcollection with just the fields you need is a great way to reduce the bandwidth needed to load the data.

There is nothing built into Firestore to create those derived documents, but it's fairly easy to build something using Cloud Functions. Create a function that responds to a Firestore onWrite trigger, and write the subset of the data to its destination there. It's common to have a separate Cloud Function for each such use-case, and I regularly see projects with 100 such functions.

I expect we'll also start seeing Firebase Extensions for this type of thing, but right now no-one seems to have built one.