[Docs] Top-down (swagger gen) app tutorial

[b-admike]

Story

As a LoopBack4 user, I would like an easy to follow and intuitive tutorial which shows me how to make a LB4 app using a top-down approach, where I start with a swagger definition.

Acceptance Criteria

TBD

[bajtos]

Top-down approach is out of scope of MVP.

[dhmlau]

related to #725

[dhmlau]

@strongloop/sq-lb-apex @bajtos @raymondfeng @hacksparrow, now that we have lb4 openapi command and the docs page https://loopback.io/doc/en/lb4/OpenAPI-generator.html. I'm thinking we can close this task as done. What do you think?

The blog post from @raymondfeng (https://strongloop.com/strongblog/loopback4-openapi-cli/) covers this topic more in depth and contains more examples. If you think the current docs is not sufficient, we can move some of the content in that blog to our documentation as well.

[jannyHou]

I am good to close this issue, or add a section for "api definition first approach" under the "Best Practice"
https://loopback.io/doc/en/lb4/Best-practices.html.
Mention that with a lb4 app, users can generate artifacts from an existing OpenAPI spec file, then point to the generator page and blog.

[bajtos]

Please note that top-down approach is not about taking an OpenAPI spec file and generating TS code with @get and @param decorators. In the top-down approach, the OpenAPI spec is the source of truth about the operations and their parameters. The TypeScript code is providing only implementation of the individual endpoints, using OAI extensions like x-controller-name and x-method-name to link endpoints with controller methods.

The problem of the lb4 openapi approach is that when the OpenAPI spec file changes, there is no easy way how to apply those changes to the generated code.

[stale]

This issue has been marked stale because it has not seen activity within six months. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository. This issue will be closed within 30 days of being stale.

[stale]

This issue has been closed due to continued inactivity. Thank you for your understanding. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository.