kimvanrenterghem / eventsoursingworkshop

workshop for eventsoursing

Event Sourcing Workshop

workshop for event sourcing

This app is a tutorial to get the feeling what you can do with event sourcing.

1. create workspace :

   1. unzip the event store in the tools folder
   2. unzip the curl in the tools folder
   3. add the C:\curl\ and C:\eventstore\ path to the PATH Environment Variable in Windows
   4. start event store

      EventStore.ClusterNode.exe --db C:\eventstore\db --log C:\eventstore\logs --run-projections=all --start-standard-projections=true

      now you can watch your store at http://127.0.0.1:2113/ user: admin pass: changeit

2. start and stop the song through the api and fire the events

   look in the web tool at the events

3. create app which displays the playing song for a user

   do this by reading only the last event of the stream (position -1)

   var eveTask = connection.ReadEventAsync(stream, -1, true);
   var eve = eveTask.Result;
   
   var ev = eve.Event?.Event;
   if (ev != null)
   {
       //event type validation
       var json = Encoding.UTF8.GetString(ev.Data);
       var songStart = JsonConvert.DeserializeObject<SongPlayingStarted>(json);
   }

4. add and remove the songs from a playlist through the api and fire the events

5. create a playlist from the playlist stream

   read the playlist stream and project it into the model

   update projection $by_category set - to _ create new projection with the following script

   fromCategory('playlist')
   .foreachStream()
   .when({
       PlayListCreated: function(state, ev){
       linkTo('playlist', ev)         
       }      
   });

   now all PlayListCreated events are linked to the stream Playlist !! for this to work all streams should be lower case and have a - between the streamname-id

   public delegate IProjector ProjectorFactory();

       public async void Start(string streamName, ProjectorFactory projectorFactory)
       {
           var projector = projectorFactory();
   
           long pos = 0;
           while (true)
           {
               var slice = await _connection.ReadStreamEventsForwardAsync(streamName, pos, 5, true);
               if (pos < slice.NextEventNumber)
               {
                   pos = slice.NextEventNumber;
   
                   //create a stream for all the linked streames
                   foreach (var e in slice.Events
                       .Where(e => e.Link?.EventType == "$>"))
                   {
                       Start(e.Event.EventStreamId, projectorFactory);
                   }
   
                   var nonlinks = slice.Events
                       .Where(e => e.Link == null)
                       .ToList();
   
                   projector.Project(nonlinks);
   
               }
               else
               {
                   await Task.Delay(100);
               }
           }

6. give top 10 list of most played songs

   do this by reading all the user play streams and rating the number of times a song is played afterwards you can order them and create a new play list create new projection with the following script

   fromCategory('usersong')
   .foreachStream()
   .when({
       $any: function(state, ev){
       linkTo('songs', ev)         
       }      
   });

7. a song should at least play for 20 sec to get in the list (rebuild your list)

   change the preview step, drop the db and restart from position 0

8. a song which is stopped and started in the same second should be considered not stopped (rebuild your list)

   change the preview step, drop the db and restart from position 0

9. create linked songs based on other users next 2 songs most played