Migration Guide: Discuss life cycle differences between LB3 and LB4

[aharbis]

Suggestion

This is a spin-off from a discussion on PR #3922.

The purpose of this issue is to discuss the life cycle differences between LB3 and LB4, with a primary goal of identifying pain-points during migration in regards to this topic.

Use Cases

Some initial topics or points of interest:

• End-to-end request-response sequence
• Out-of-the-box data parsing and validation provided by LoopBack
• Various points to mount custom data validation for a given request / transaction
• Operation hooks(interceptors in lb4)/remote hooks and their equivalents in LB4
• differences of operations between LB3 and LB4 such as boot, injection.
• datasource interceptor in lb4
• How to migrate boot scripts How to migrate boot scripts #3957 might be related

Since it's life cycle, this should be a high level view

Examples

Acceptance criteria

TBD - will be filled by the team.

• add these topics to the migration guide doc(s)
• blog about this doc

[dhmlau]

@bajtos , could you please add the acceptance criteria so that the team can estimate? Thanks.

[dhmlau]

Discussion with @hacksparrow:
It seems like the scope of this task is not clear. A few things to figure out:

• does it make sense to work on this task now while we're still working on other parts of the migration guide?
• does it make sense to break the task down into a smaller pieces first?

[dhmlau]

@hacksparrow, let me assign it to you for now, because you indicated that you'll be looking into the scope of this task. Thanks.

[hacksparrow]

https://loopback.io/doc/en/lb4/Understanding-the-differences.html already contains the broad differences between LB3 and LB4.

"Operation hooks(interceptors in lb4)/remote hooks and their equivalents in LB4" is covered by
https://loopback.io/doc/en/lb4/migration-models-overview.html.

"How to migrate boot scripts #3957 might be related" is covered by https://loopback.io/doc/en/lb4/migration-boot-scripts.html.

"Datasource interceptor in lb4" is covered by https://loopback.io/doc/en/lb4/Interceptor-generator.html.

For the remainder, I am suggesting to create the following pages under the Migration Guide.

• Request-response cycle
  • Document the request response cycle in LB3
  • Document the request response cycle in LB4
• In-built data parsing and validation
  • Document in-built data parsing and validation in LB3
  • Document in-built data parsing and validation in LB4
• Custom validation
  • Document the points where data (request / transaction) can be accessed and validated in LB3
  • Document the points where data (request / transaction) can be accessed and validated in LB4

Let's create three new tasks, with the sub points as the acceptance criteria.