Aggregating value from multple projections

EventStoreDB
1

I’ve created a projection called MSP which aggregates monthly streams for all users as follows

fromCategory(‘MonthlyStream’)

.foreachStream()

.when(

{

“$init” : function(s,e) { return {count:0, type:{}}},

“$any” : function(s,e) {

s.count += 1;

var key = e.body.Reason;

var val = s.type[key];

s.type[key] = !val ? e.body.Change: val += e.body.Change;

}

})

This creates an aggregated value per monthly stream which I can access using MSP/state?partition=MonthlyStream-MemberId-2015-6

Is there a way for me to aggregate the monthly values into a yearly aggregate across all members? Ideally I’d write something along the lines of

fromCategory(‘MonthlyStream-MemberId’)

.foreachStream()

.when(

{

“$init” : function(s,e) { return {count:0, type:{}}},

“$any” : function(s,e) {

s.count += 1;

var key = e.body.Reason;

var val = s.type[key];

s.type[key] = !val ? e.body.Change: val += e.body.Change;

}

})

But I can’t get a category which groups all monthlystreams per member

Thanks

2

Given that MemberId changes of course

3

Is an internal projection the right place to do this? I would imagine
this to be trivial as an external projection to some read model.

4

Do you mean to consume the entire stream for the member and aggregate it when requested?

5

Let's imagine I had a catch up subscription and I wrote to mysql. This
would seem to be a pretty trivial query at that point.

6

Would a catch up subscription written using the C# ClientAPI not be a one off projection instead of a continuous one? I’d want to have a continuous projection so the running totals are up to date. Also if there are a lot of events the internal projections stores the checkpoint of how far along the stream it has reached.

Also I intended to calculate all the monthly statements up front instead of creating them when they are requested.

7

A catch up subscription will read forever. I would checkpoint such a
thing from outside

8

At the moment I’m pushing all account changes into one stream, then partitioning them by member id to a member stream then again into a monthly stream per member.

Is it better to consume these streams with an external projection using the C# ClientAPI rather than creating aggregation projections in GES?

Would I then have a catch up subscription to the member stream and have a sql row per member?

I was trying to compose the annual aggregation from the monthly aggregations, perhaps this is not the right approach when using GES.