feat(version) Automatically determine the database version when creat…

[janmeier]

…ing the first connection. Re-roll of #3842

Should be good to go, just want to get a quick review on it :)

[BridgeAR]

A Promise should always return something in the middle of a promise chain so I recommend to rewrite this to:

var promise;
if (self.sequelize.options.databaseVersion === 0) {
  promise = self.$connect(self.config)...;
} else {
  promise = Promise.resolve();
}
return promise.then(function () { ... });

Or:

return Promise.try(function() {
  if (self.sequelize.options.databaseVersion !== 0) {
    return;
  }
  return self.$connect(self.config)...;
}).then(...);

[mickhansen]

return; would not be returning something, i don't really see the importance in any case, but up to @janmeier

[mickhansen]

Although i do generally prefer short circuit code like your second example, although that example will still race.

[BridgeAR]

return; is sugar for return undefined;. So it'll return undefined and not nothing ;). I personally use return void 0; but that's just something I got used to quite a while ago. If you do not return something in the middle of a promise chain the promise thinks it's done and has to realize that there's another then chained.

[BridgeAR]

LGTM with one small comment

[mickhansen]

This will race, won't it?

[janmeier]

If several concurrent calls request a transaction yes. The other alternative is to block once the first call is sent, but it would make the code slightly more complicated. I don't really think its a big problem that call getversion maxConnections number of times :)

[mickhansen]

Just if you have several concurrent calls i assume? Each will request a new connection from the pool.
Blocking would not be too tricky, save the connect + databaseversion promise in a variable, if var is set use that to resolve.

[janmeier]

Yep, nothing to do with transaction :)

[janmeier]

Updated, thanks for the feedback @mickhansen and @BridgeAR :)