Filtering projections

EventStoreDB
1

How i’m trying to get the projections working but i dont see clearly how they do.

working on the example of the chating room i can see how to get new messages but:

  • ¿How can i get all the messages posted by one given user?
  • ¿how can i get all the events of the type UserJoinedChat to compare diferents chats usage?
    Thanks.
2

So to be clear you want all the chats of one user to be in one stream
say /streams/{username} and you want a stream of all the UserJoined
events?

3

Assuming I am correct. Here is a rough typing of the first one.

fromAll().whenAny(
                    function(s, e) {
                            link_to(e.user, e);
                            return null;
                    });

What this does is create a stream name {e.user} that contains links to
events in other streams that the user did.

Example:

in chat room 1. Greg says "hello"
in chat room 1 Neringa says "hi!"

in chat room 2 Neringa says "Hi Greg"
in chat room 2 Greg says "more stuff"

in chat room 47 Greg says "hello"
in chat room 47 Tom says "yo"

would be your initial streams. That projection will create streams

/streams/Greg
in chat room 1. Greg says "hello"
in chat room 2 Greg says "more stuff"
in chat room 47 Greg says "hello"

/streams/Neringa
in chat room 1 Neringa says "hi!"
in chat room 2 Neringa says "Hi Greg"

/streams/Tom
in chat room 47 Tom says "yo"

So now if I wanted to write a projection to count how many chats
people sent I could do a foreach on the Greg/NEringa/Tom streams.

Make sense?

Cheers,

Greg