CODEWITHSUNDEEP
oopdomain-driven-designcqrs
Divyesh
Divyesh

Reputation: 21

How to Model Complex Query Classes in CQRS

How to Model Query classes (CQRS), given that data is accumulated from various places and business logic is then run on top of this data. Currently, we have code to pull out required data in Manager class and business logic in Domain Model. Is there a better way. high level suggestions will help. Hiererachy is webapi Controller-> Manager -> DomainModel |-> Infrastructure( to get required data)

Upvotes: 0

Views: 848

Answers (2)

Boris Guéry
Boris Guéry

Reputation: 47614

Generally speaking, write models (generated from Commands) are not mirroring the read models (fetch from the Queries).

Write models (Aggregate Roots) are designed to ensure consistency and invariants of a domain, while read models are mostly used to build UI and/or an API.

If you design a simple domain for a Blog, you may have a Post aggregate and PostSummary as well as PostDetails or even a simple Post.

Both named similarly but in a different context of use.

Your Aggregate will probably refers its author only by reference (id) while your read model may be a flattened and pre-built with all the necessary informations required for your UI.

You end up with two models where your Aggregate does not even expose any getters (that's the read model purpose).

Upvotes: 2

Brad Irby
Brad Irby

Reputation: 2542

It sounds like you're doing just the C part of CQRS, not the Q. In CQRS there are 2 data models, one that is updated via commands (the write model) and one that is custom made just for display purposes (the read model). when a command makes a change to data, it loads a full aggregate with business rules from the write model, makes appropriate changes, and saves. It then (usually by sending a message) requests an update of the read model.

The read model is a collection of tables that are custom built for specific target UI pages. Data duplication is everywhere. The idea is that reads should be very fast because they are just a "select *" query from the read table.

If you had implemented a read model, then your question doesn't make sense because there are no complex query classes. If you've not implemented CQRS, then normal advice would apply, such as creating repositories to contain the query, etc.

Upvotes: 0

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