问题
We are using fast render in our app, so all the data the app needs is sent down with the app itself. We are not using any Meteor.subscribe calls since minimongo is populated by fast render.
Once rendered we run Meteor.disconnect()
At some point in the future we want to reconnect to call a specific method, but when we reconnect, minimongo gets cleared.
How can we prevent Meteor from clearing all documents in minimongo upon reconnect?
回答1:
I suspect that it's actually fast render that is causing your problem. Checking the meteor docs for Meteor.disconnect()...
Call this method to disconnect from the server and stop all live data updates. While the client is disconnected it will not receive updates to collections, method calls will be queued until the connection is reestablished, and hot code push will be disabled.
Call Meteor.reconnect to reestablish the connection and resume data transfer.
This can be used to save battery on mobile devices when real time updates are not required.
This implies that your client data is never deleted, otherwise you could not "resume data transfer" upon reconnection. It also would mean that one of their primary intended use cases for this method (e.g. "used to save battery on mobile devices when real time updates are not required") would not actually work.
Just to be absolutely sure, I checked the meteor source to see what happens on a disconnect and all it does it set a connection state var to false, clear the connection and heartbeat timers, and cancels any pending meteor method calls.
Similarly, Meteor.reconnect() simply set the connection state var back to true, re-establishes the connection and hearbeat timers, re-establishes any subscriptions (so that new data can be acquired...this action does not delete client data), and calls any queued up meteor method calls.
After reading more about how fast render works, I understand that a lot of hacking was done to get it to actually work. The main hack that jumped out to me is the "fake ready" hack which tricks the client to thinking the subscription is ready before the actual subscription is ready (since the data was sent to the client on the initial page load).
Since you have no subscriptions in your app and a Meteor.reconnect() does not cause your page to reload, I'm wondering if the client is never doing anything because it never receives another ready message. Or maybe since Meteor isn't aware of any subscriptions (since fast render bypasses meteor to transport data), is clears the client minimongo cache so its in a good state if a new subscription is started. Or, there could be something else about fast render that is getting in the way.
Long story short, I'm quite certain that Meteor.disconnect() and Meteor.reconnet() have no impact on your client minimongo data based upon reviewing the documentation, the source, and based upon my experience of testing my meteor apps offline.
I can Meteor.reconnect() does not delete data as I have a meteor app in production that continues to call Meteor.reconnect() if it detects that it has lost a connection (e.g. the computer goes offline, network outage, etc.).
Hopefully this long winded answer helps you track down what's going on with your app.
回答2:
I tried Meteor.disconnect() and Meteor.reconnect() and the Minimongo DB was not cleared. I confirmed it using:
a) Minimongo explorer: https://chrome.google.com/webstore/detail/meteor-minimongo-explorer/bpbalpgdnkieljogofnfjmgcnjcaiheg
b) A helper to return a message if at some point during reconnection
my collection would have zero records.
Although you are right, all the data in the subscription was sent from server to client after reconnection (letting the local DB to do the sync stuff though). This happens because Meteor server takes the reconnection like a completely new connection. It seems like in the future (uncertain) Meteor will deploy a real reconnection, as is stated in their docs:
Currently when a client reconnects to the server (such as after temporarily losing its Internet connection), it will get a new connection each time. The onConnection callbacks will be called again, and the new connection will have a new connection id.
In the future, when client reconnection is fully implemented, reconnecting from the client will reconnect to the same connection on the server: the onConnection callback won’t be called for that connection again, and the connection will still have the same connection id.
Source: https://docs.meteor.com/api/connections.html
来源：https://stackoverflow.com/questions/43007627/when-i-run-meteor-disconnect-and-then-meteor-reconnect-meteor-clears-minimo