refactor: migrate models from cli

[jannyHou]

connect to #4521, prepare for User model migration

address comment #4706 (comment)

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• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

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[agnes512]

It's nice to see an example uses CLIs to import models from LB3 and also create LB4 relations 👍 I like the improvement of consistency.

[agnes512]

I have a few concerns here but they might not be related to the PR itself:

• Is settings. idInjection from model migration? While I was doing task docs: update Models.md #4829, I removed idInjection from the LB4 docs because it doesn't work when I tested it ( I might test it incorrectly)
• LB3 uses id: 1 cause it allows composite ids, and 1 indicates true and also its index. Ideally we should just use id: true for imported models.

[jannyHou]

@agnes512 I didn't have it before, it's generated by the migration CLI. If it's not correct, I think we'd better fix it from CLI side.

[agnes512]

True, but I don't know how much effort it needs

[jannyHou]

ah got it after reading the story #4829 , let me remove them.

[agnes512]

I check what @bajtos did in his PR: https://github.com/strongloop/loopback-next/pull/4737/files#r383816292

And this is what I tried:

1. Define a LB4 model with idInjection: true

  settings: {
    idInjection: true,
  },
})
export class User extends Entity {
  // @property({   // no id property defined
  //   type: 'number',
  //   id: true,
  //   generated: true,
  // })
  // id?: number;

  @property({
    type: 'string',
  })
  name: string;
...
}

2. then run migration-> failed.

I am not hundred percent sure if idInjection works in LB4. I am okay to keep it for sake of consistency.

[jannyHou]

@agnes512 many thanks for double checking and verifying with code!

I am okay to keep it for sake of consistency.

If it causes failure I'd like to remove in the example, I can investigate a bit (after having PR ready for #4521) and create issue/PR to fix if needed.

[dhmlau]

nitpick: there's an extra spacing.

[dhmlau]

LGTM. Thanks!