Catchup Subscription

EventStoreDB
#1

Hi,

I’m trying to use SubscribeToStreamFrom to build my read models. Writing a windows service to subscribe to the streams that will process the events (<-- is this an OK approach or some thing else is favoured?).

The SubscriptToStreamFrom method expects the event number. However, it seems it actually works on the Stream position. Where do I get that value from to store so that next time I can process the next event. EventStoreCatchUpSubscription does not seem to have the LastProcessedEventNumber that EventStoreStreamCatchupSubscription has.

The other question is, do I unsubscribe (stop) the subscription each time and subscribe again to process the next event?

Thanks,

Qudoos

#2

The only time you should be resubscribing is on subscription lost /
restarts of your client (eg client remember the last event sequence
you processed and hands it back on a restart).

https://github.com/EventStore/EventStore.Samples.Dotnet/blob/master/CatchupSubscription/Program.cs

#3

Thanks Greg.

In that example

Console.WriteLine("Received: " + x.Event.EventStreamId + “:” + x.Event.EventNumber);

Is Event.EventNumber the thing I got to hang on to when I restart?

#4

Yes.

#5

Just to be clear thats assuming no linktos etc OriginalPosition is safe to use with either

#6

ah! Yes, so I don’t get the event data (Event.Data) unless I pass resolvelinktos=true.

#7

by the way I am testing this off of the $ce- projections…

#8

yes otherwise your event data will be what is actually in the stream which is a $> event with a body 1734@somestream resolve linkto will resolve that event

#9

That does make sense. But in this case i.e. resolvelinkto= true, the event number does not seem correct. It is being repeated. I have 3 events on my aggregate…for each event it retains the value 0,1,2 in the $ce- projection. I want the $ce event number not the actual event number (which I am only getting when resolvetolink=false).

#10

See previous post about using OriginalEventNumber that works in both cases.

#11

https://github.com/EventStore/EventStore/blob/release-v3.6.0/src/EventStore.ClientAPI/ResolvedEvent.cs#L49

#12

That works.

Much appreciated, thank you.