Native async/await and upgrade handlers

[sechel]

Hi, I'm currently trying to upgrade my codebase to native es2017 and especially native async/await. I am aware that I will have to to do some extra work to include Firefox. This is the story about Chrome. I'm using Dexie 2.0.1 and everything seems to work well so far. The only thing that does not work is migration with async callbacks. I prepared a JSFiddle to illustrate this (This contains also a version with pure then callbacks and a version involving generator functions both of witch work fine): https://fiddle.jshell.net/sechel/06gcbbpL/

let db = new Dexie(dbName);
db.version(1).stores({test: '++id'});
let data = {id: 1, value: 1};
await db.test.put(data);
db.close();
let migrated = new Dexie(dbName);
migrated.version(1).stores({test: '++id'})
migrated.version(2).stores({test: '++id, value'}).upgrade(async t => {
console.log('2 start');
await t.test.toCollection().modify(d => d.value += 1);
console.log('2 mid');
await t.test.toCollection().modify(d => d.value += 1);
console.log('2 end');
});
migrated.version(3).stores({test: '++id, value'}).upgrade(async t => {
console.log('3 start');
await t.test.toCollection().modify(d => d.value *= 2);
console.log('3 mid');
await t.test.toCollection().modify(d => d.value *= 2);    
console.log('3 end');    
});  
let dataExpected = {id: 1, value: 12};
let dataMigrated = await migrated.test.get(1);
assert.deepEqual(dataMigrated, dataExpected, 'migration successfully performed');
await migrated.delete();

The console output illustrates that there is something strange going on.

2 start
3 start
2 mid
3 mid
2 end
3 end

It seems to me as if the async handlers are not called sequentially but somehow in parallel on the same transaction!? Does that make sense, am I missing something?

[dfahlander]

Ok, I think the upgraders fail to reference count the db operations as standard promises take place instead of Dexie.Promise. Reference counting is not needed with async functions and we should really respect the returned promise instead. Could be easily fixed.

[sechel]

Hi David, thanks for the reply, a fix would be great.

[dfahlander]

I'll try fix it next week. Just a note for other readers : using native (non-transpiled) async await can only work well on recent versions of Chrome, Edge, opera and Safari. Firefox still has issues when involving native promises in an indexedDB transaction, and not all users have the latest versions of their browsers. Therefore, it is still recommended to transpile async/await code using either babel or typescript if it should work on most end users browsers.

[dfahlander]

Closing as it is now resolved in master branch and will be part of next 3.0.0-release.