Publicize `ParseQuery.fromNetwork()` & allow multiple `find()`/`count()`

[grantland]

ParseQuery.fromNetwork() would be useful for toggling a query .fromLocalDatastore() <-> .fromNetwork() to mimic CACHE_THEN_NETWORK and CACHE_ELSE_NETWORK from query caching.

We already have the private API, so it'd be super easy to enable this.

We'd also need to remove the limitation of mutating an inflight query, which should be fine since we now since ParseQuery.State is passed to the controller as an immutable object.

[chrisjenx]

👍 on creating a immutable state when creating a Task so we can keep mutating the builder.

Not sure if fromLocalDataStore() explicitly means CACHE_THEN_NETWORK.

Generally when chaining queries, I want to know what they are doing. So I would concat .fromLocalDatastore with .fromNetwork to create a CACHE_THEN_NETWORK.

Exposing them should make it much easier for people to consume the tasks directly.

[satyadeepk]

@grantland I would like to pick up this. Can you be more specific on how .fromLocalDatastore() and .fromNetwork() corresponds to CACHE_THEN_NETWORK and CACHE_ELSE_NETWORK ?

Is it a chaining like @chrisjenx mentioned?

[grantland]

@satyadeepk Then it's yours! You are correct, this change would allow developers to emulate CACHE_THEN_NETWORK and CACHE_ELSE_NETWORK by using public ParseQuery APIs:

CACHE_THEN_NETWORK

final ParseQuery<ParseObject> query = // ...
query.fromLocalDatastore().findInBackground().continueWithTask((t) -> {
  // Update UI with results from LDS
  return query.fromNetwork().findInBackground();
}).continueWithTask((t) -> {
  // Update UI with results from Network
  return t;
});

CACHE_ELSE_NETWORK

final ParseQuery query = // ...
query.fromLocalDatastore().findInBackground().continueWithTask((t) -> {
  if (t.isFaulted() 
      && t.getError() instanceof ParseException 
      && ((ParseException) t.getError()).getCode() == ParseException.CACHE_MISS) {
    return query.fromNetwork().findInBackground();
  }
  return t;
}).continueWithTask((t) -> {
  // Update UI with results
  return t;
});

s/fromLocalDatastore()/setCachePolicy(CachePolicy.CACHE_ONLY)/g and s/fromNetwork()/setCachePolicy(CachePolicy.NETWORK_ONLY)/g without LDS.

[satyadeepk]

Gotcha, I just made fromNetwork() public and both your above use cases worked as expected. Mutable inflight query is not required for these two cases, because the second query happens after the first one is completed - Am I right?

Also, to make the query mutable inflight, I am thinking of bypassing checkIfRunning in ParseQuery.doWithRunningCheck and all query methods like whereEqualTo. Do you forsee any side effects of doing that? Or is there a better way of doing it?

[grantland]

Yeah, that's correct. We've added the immutable ParseQuery.State which is in the beginning of all "inflight" entry points and is used for all query properties so there shouldn't be any issues with removing this limitation. In addition, it would allow a slightly faster approach for CACHE_THEN_NETWORK:

ParseQuery<T> query = //...
final Task<Void> network = query.fromNetwork().findInBackground().continueWithTask((t) -> {
  // Update UI
  return t;
}, singleThreadExecutor);
final Task<Void> local = query.fromLocalDatastore().findInBackground().continueWithTask((t) -> {
  if (network.isCompleted) {
    return t;
  }

  // Update UI
  return t;
}, singleThreadExecutor);

[danielapsmaior]

Hi, I'm on version 'com.parse:parse-android:1.13.0' and I can't see query.fromNetwork(). Was it reverted? On my ParseQuery.java, there is:

/* package */ ParseQuery<T> fromNetwork() {
    checkIfRunning();

    builder.fromNetwork();
    return this;
  }

[grantland]

Nothing was ever merged in for this