I have recently been building an application on top of Greg Young EventStore as my peristance layer and I have been pondering how big should I allow an event to get?
For example I have an UK Address Aggregate with the following fields
UK_Address
-BuildingName
-Street
-Locality
-Town
-Postcode
Now I'm building the UI using React/Redux and was thinking should I create a single FAT addressUpdated Event contatining all the above fields?
Or should I Create a event for each of the different fields? and batch them within the client until the Save event is fired? buildingNameUpdated Event, streetUpdated Event, localityUpdated Event.
I'm not sure if the answer is as black and white ask I have asked it what I really would like to know is what conditions/constraints could you use to make the decision?
You have to bundle al the information together in one event when this data has to be consistent with each other.
So when you update one field of an address you probably get an unwanted address. This will happen when the client has not processed all the events at a certain time due to eventual consistency.
Example: Change address (City=1, Street=1, Housenumber=1) to (City=2, Street=2, Housenumber=2)
When you do this with 3 events and you have just processed one at the time of reading you could get the address: (City=2, Street=1, Housenumber=1).