Vertical Slices in .NETBojan Veljanovski, CTO at HASELT

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What is an user’s intent in software?

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User Intent - Reads and Writes

- WRITE is a request modeled as COMMAND triggered via HTTP POST

- READ is a request modeled as QUERY triggered via HTTP GET

- Commands modify data

- Queries retrieve data

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User Intent - CQRS

CQRS is a simple pattern, writing and reading data is placed in 2 separate classes which have single responsibility.

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DISCLAIMER

Nope… there is no silver bullet.5

What we are going to talk about

- Overview

- Horizontal vs. Vertical user stories

- Horizontal vs. Vertical slices

- Commands & Queries

- Feature folders

- DEMO code

- Summary

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“Two“ starting points to build a system

- Horizontal first

- Vertical first

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Horizontal vs. Vertical user stories

- Horizontal- Story 1: Create the new DB Table for Users

- Story 2: Create the DAL to access the DB Users

- Story 3: Create the Users business layer code that references the DAL

- Story 4: Write the Users UI screen

- Vertical- Story 1: User can register and provide username and

password.

- Story 2: User can manage multiple addresses.

- Story 3: User can add additional contact fields (phone, email, etc).

- Story 4: User can subscribe to a subscription plan.

- Story 5: Admin can manage subscription plans and pricing.

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Horizontal vs. Vertical user stories

- Horizontal- Implement the database layer for A, B and C- Implement the business logic layer for A, B

and C- Implement the user interface for A, B and C

- Vertical- Implement A from end to end- Implement B from end to end- Implement C from end to end

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Horizontal slicing is not natural in agile

- Changes usually happen vertically - You limit your application to the same horizontal

constraints for all features (regardless of the size and complexity)

- ...and more

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“Slicing” is a team organization thing too!

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Vertical Slices over Horizontal Slices

- Horizontal slices is organization by technical layers.

- Vertical slices is organization by features (business requirements).

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Vertical Slicing: The Stakeholder

Stakeholders talk and eat the cake in vertical slices. They want one delicious piece at a time, not only the vanila part.

Why don't we structure our code vertically as well?

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Horizontal Slices

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Horizontal Slices (2)

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Horizontal Slices (3)

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Vertical Slices

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Organization structure

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Addressing cross-cutting concerns

- Loggers- Validators- Transactions

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ASP.NET MVC - Feature Folders ViewEngine

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ASP.NET MVC - Feature Folders ViewEngine

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Can it easily evolve to CQRS?

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Can it easily evolve to SOA/Microservices?

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SUMMARY: Characteristics of good Vertical Slices- Code is structured primarily by feature,

secondary by layer- Have single responsibility (business-oriented)- Encapsulated and decoupled from other slices

- Complexity and defects are isolated in each slice, instead of each layer

- Increases developer’s understanding of each feature as a whole

- Enables incremental releases of features- Enables faster feedback loop- Enables support for potential simpler scaling out

- By Read/Write mechanics (CQRS), or- By Feature as a whole (SOA)

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SUMMARY: Trade-offs and Challenges

- Complete mindset shift

- Developers must be all-round-shaped (back, front, middle, db, all)

- Now you have twice as many classes as before

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