Allow emulators to export on exit

[samtstern]

Originally requested through FIrebase support, there is some demand for a flag like this:

firebase emulators:start --import=./seed --export-on-exit

This would import from a location but save any mutations made on exit.

[michi88]

I've requested this indeed! Great that it is actually picked up here :). I could try to make a PR if that is appreciated. Let me know.

[samtstern]

@michi88 if you're interested in sending a PR for this I'd be happy to accept it. But we have to follow a bit of a process:

1. First you and I should work out the full API change here
2. Then I'll "sponsor" your internal API proposal, we have a group of Firebasers that reviews any API change to our SDKs or the CLI.
3. Once it's approved we can merge and release your PR, along with any edits suggested by the API review process (2).

Sound like something you're up for? I know it sounds slow and bureaucratic but I'll be handling the bad parts mostly.

[michi88]

Great, I’m up for giving that a try! So let’s settle on the API. What do you think about the —export-on-exit flag? Should it just be a flag or accept a path where to export the data to? Should it require the —import flag and take that folder to export to by default?

My general use case here is with :exec in the ‘default’ npm serve command that would start emulators but the data is not gone when you stop / reload. Of course you can do an export first and all but that is too much explaining for new developers coming to a project and expect things to just work with a single npm serve command.

What might make sense though is that the —import dir contains seed data (that you store in a repo) for new setups but that you can use a different dir as your local data dir where we would export and import to on subsequent runs. So maybe we would add another —seed flag that is only imported when the —import dir is empty.

Not sure what would be best here. Let me know what you think.

[samtstern]

@michi88 thanks for asking all the right questions. My personal take:

• I like the name --export-on-exit

• I think it should take an optional path --export-on-exit=./some-path. When unspecified it would use the same path as --import. If you do a bare --export-on-exit with no --import=something flag that's an error. So:

  • ✅ VALID: emulators:start --import=./foo --export-on-exit
  • ✅ VALID: emulators:start --import=./foo --export-on-exit=./bar
  • ✅ VALID: emulators:start --export-on-exit=./bar
  • ❌ NOT VALID: emulators:start --export-on-exit

If that sounds good to you I'll propose it to the API people.

[michi88]

I'm leaning towards that indeed as we have this --import flag already to work with.

On the other hand something like a --data-dir would maybe also make sense where we import from and export to. It feels a bit cumbersome that we need to set 2 flags in order to get this behavior (importing and exporting).

I'd say the --import flag is super useful for seeding data for tests and the --data-dir is what you want during development.

The downside of this is that we're actually not really using it as a persistent data dir but only export on exit (which is not guaranteed to succeed). Unless we can change that and use it like that (in the future) but that is doubtful.

I'm ok with --export-on-exit as well though :).

[samtstern]

@michi88 totally makes sense, although right now we do want import and export to feel explicit and separate for the reason you said: they're one-time expensive operations. Something like --data-dir implies that these emulators have a persistence layer, which they do not.

I'll go ahead and kick this off.

[samtstern]

Alright I sent out the API proposal so we'll see how it goes.

For googlers: http://go/firebase-emulators-export-on-exit

[samtstern]

@michi88 thanks for your patience, the API proposal was approved today! I think this is all stated above but here's a succinct version of the proposal you can use for your implementation guide:

# VALID: This would export to the same directory as import (./data)
$ firebase emulators:start --import=./data --export-on-exit

# VALID: This would export to a brand new directory
$ firebase emulators:start --import=./data --export-on-exit=./new-data

# VALID: No import is required to export
$ firebase emulators:start --export-on-exit=./new-data

# INVALID: In this case we don't have an --import flag to infer the directory
$ firebase emulators:start --export-on-exit

Of course if your circumstances have changed and you no longer want to implement this just let me know and I will happily do the PR myself.

[michi88]

I’ll have a look right now, keep you posted.

[quantuminformation]

Waiting with anticipation. I didn't realise that data was not saved automatically after restarting and was wondering what was wrong with my app until I checked the db, I'm glad I'm not crazy.