How do I change the read model in cqrs? - events

Question

I'm new in cqrs user.
I have event in
id agg event payload time
1 member MemberCreated {id:1,user:yumi,age:21 ...} 2021-06-10
2 member MemberUpdated {id:1,user:yumi,age:25 ...} 2021-06-10
3 member MemberDeleted {} 2021-06-11
and, my ask is
How does the read model change based on events 1-3 above?
first scenario :
1 event in readmodel :
{id:1,user:yumi,age:21 ...}
1 row in readmodel
2 event in readmodel :
{id:1,user:yumi,age:21 ...}
{id:1,user:yumi,age:25 ...}
2 row in readmodel
3 event in readmodel :
{id:1,user:yumi,age:21 ...}
{id:1,user:yumi,age:25 ...}
{}
3 row in readmodel
or update only read model ??
second scenario :
{id:1,user:yumi,age:21 ...}
->
{id:1,user:yumi,age:25 ...}
->
{}
I am very confused about this issue. Any help would be appreciated.

Answer 1

Please note, that your events are always related to some DDD aggregate with an ID, so there should be an aggregateID column in your event table.
The answer depends on what do you want to have in your read model. For instance if you want to have some Members table with a row for each member, then in pseudocode I would do it like this:
switch(e.event) {
case MemberCreated:
db.Insert(Members, {
id: event.aggregateID,
user: e.payload.user,
age: e.payload.age}
)
break
case MemberUpdated:
db.Update(Members, {
id: event.aggregateID,
user: e.payload.user,
age: e.payload.age}
)
break
case MemberDeleted:
db.Delete(Members, {id: event.aggregateID})
break
}
But if you want to have some MemberCount table with number of members, you would increment it on MemberCreated and decrement on MemberDeleted.
If you want to have an AuditLog table, then you would just add a row about what happened on each event.