Hey,

I am actually interested in Event Sourcing for literally years but haven’t used it yet. Last night, I read through the guides in the Commanded documentation and watched the linked 20 minutes talk on Youtube.
The provided examples start to make sense and the overall picture becomes more clear.

Now, I have a project idea in mind for a very long time, which involves a rating system. I knew right from the start that this rating system would be a good opportunity to use Event Sourcing. However, this rating system will be a little bit more complicated in terms of aggregation and business rules.

Let me show you the concept:

The following will be my logical structure:

- parent
--- child
------category_a
------category_b
------category_c
--- category_1
--- category_2
--- category_3

• parent and child are the actual things I want to be rated.
• a child has a dynamic list of categories to be rated on, that can change over time, so they have just an identifier, e.g. usability (%RateCategory{subject: "id-of-child", name: "usability", score: 8})
• a parent also has a dynamic list of categories to be rated, same as child
• some parents are not ratable, depending on their type
• the overall rating of a child is a combination of all category ratings for it
• if a parent is ratable, it has two overall ratings
  • one overall rating as a result of combining its category ratings
  • another rating that combines the overall rating of its children

Here comes the tricky part:

I want to have the concept of rating periods. I am not sure yet how long a period should be, but as soon as one period ends, another starts immediately. This is to track “progress” over time.
In each rating period, a user can rate only once.
Let’s say, there is a rating period every month. In January, a user can rate all categories of a parent and child. Then, in February, the ratings will be “reset” and the user can rate for everything again.

The goal is to track the ratings of a parent and child over time to see if things got better or worse.

So, that was my overall idea for the rating system. Everything else in the system will be done the “usual” way.

What I would like to get from you are some strategies to achieve this. Since I am just starting to get into the ES mindset, I am a bit lost as to how to implement this right now.