CODEWITHSUNDEEP
domain-driven-designcqrs
Sebastian S
Sebastian S

Reputation: 294

readmodel for available data and selected data

I'm trying to follow DDD and CQRS principles in the project I'm currently working on. I'm now struggling with a design decision. Let's say I have a page with a list of topics a users can subscribe to. The users also sees what topics he has subscribed to. How do I retrieve the data? Do I query the topics and marked topics separately.

e.g.

and then in the view I do the magic of combining the 2 so that the users sees his subscriptions. Or do I make 1 model that contains all topics and already mark the topics the user have subscribed to

e.g.

Upvotes: 0

Views: 71

Answers (2)

mrdnk
mrdnk

Reputation: 685

This really comes down to a design decision - what are you going to show the users?

  1. List of all topics and a list of current subscription
  2. All Topics and if the user has a subscrition.

If 1, you want a results view...

var resultView = new TwoResultViews(avaiableTopics, subscriptionTopics);

returns 

"res": {
  "availableTopics": 
  [
    {
       "topic": "topic1",
    }
  ],
  "subscribedTopics": 
  [
    {
       "topic": "anotherTopic"
    }
  ]
}

or if 2

var resultView = new SingleResultView(availableTopics, susbcrtiptionTopics);

returns 

  [
    {
       "topic": "topic1",
       "subscribed": true
    }
  ],

Either way, you one want 1 call to the API, unless there are obvious (and accountable - aka performance) reasons to optimise it.

Upvotes: 0

tugberk
tugberk

Reputation: 58434

Let's say I have a page with a list of topics a users can subscribe to. The users also sees what topics he has subscribed to. How do I retrieve the data?

There is various ways to do this but I would create two read models:

  • AllTopics: list of all topics
  • UserWithTopics: to see what topics a user have subscribed to.

When constructing your page, you can then use both data to see what topics users can subscribe in that page, and probably unsubscribe. As you have at most 50 topics on both ends, performance for page construction shouldn’t be an issue.

Upvotes: 2

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