how can i delete multiple paths with firebase cloud functions

Question

I want to delete data older than 15 days. Can I query and delete multiple directories at the same time?

The database structure is like this. There are multiple languages and types.

{
  "hr" : {
    "classic" : {
      "finish" : {
        "-MuJD4oAlQ42TkdfKW5M" : {
          "gid" : "LlAHMyj",
          "ts" : 6.652890289073215E8
        }
      }
    },
    "duel" : {
      "finish" : {
        "-MuJD4o9LONeayt4ACMC" : {
          "gid" : "rfePU2x",
          "ts" : 6.652890289073215E8
        }
      }
    },
    "target" : {
      "finish" : {
        "-MuJD4o9LONeayt4ACMD" : {
          "gid" : "FBz4H_4",
          "ts" : 6.652890289073215E8
        }
      }
    }
  },
  "nl" : {
    "target" : {
      "finish" : {
        "-MuJD4oAlQ42TkdfKW5L" : {
          "gid" : "sv3pRfC",
          "ts" : 6.652890289073215E8
        }
      }
    }
  }
}

I tried to do it with the code below but it always returns null.

exports.deleteOldData = function (snap, context) {
  const end = new Date(new Date().setDate(new Date().getDate() - 15));
  const endDate = toSwiftDate(end);

  database.ref("/matchTour/{language}/{type}/finish/").orderByChild("ts").endAt(endDate).transaction(function (info) {
    if (info === null) return info;
    console.log("matchTour 3", JSON.stringify(info.val()));
    return null;
  }).catch((error) => {
    console.log("error);
  });
};

Answer 1

You can't run a transaction on a query. In fact, from looking at the reference documentation for Query this shouldn't even compile.

This should be closer:

exports.deleteOldData = function (snap, context) {
  const end = new Date(new Date().setDate(new Date().getDate() - 15));
  const endDate = toSwiftDate(end);

  const ref = database.ref("/matchTour/{language}/{type}/finish/");
  return ref
    .orderByChild("ts").endAt(endDate)
    .once("value")
    .then((results) => {
    let updates = {};
    results.forEach((snapshot) => {
      updates[snapshot.key] = null;
    });
    return ref.update(updates);
  }).catch((error) => {
    console.error(error);
  });
};

The above reads the results for the query from the data, performs a single multi-path update to delete all of them, and ensures the the promises returned by the asynchronous read and write bubble up, so that your Functions container doesn't get terminated prematurely.

---

That leaves the question of what language and type are in database.ref("/matchTour/{language}/{type}/finish/"). If there are meant to be variables that come from the context, you'll want to use backticks for this string:

database.ref(`/matchTour/{language}/{type}/finish/`)

---

All in all there are quite a few mistakes in this code that make me think you may not yet be too comfortable with writing server-side JavaScript. If that is the case, writing Cloud Functions is not the easiest way to get started, and I recommend first writing the same code in a client-side JavaScript environment, like a local node.js script, or even a web page.

Reading the Firebase documentation for Web developers and/or taking the Firebase codelab for Web developer are great starting points.