feat(rest): refactoring common filter schemas

[achrinza]

Related: #4290 (comment)

Currently, the filter schemas are generated inline in the OAS openapi.json document. This may lead to the filter schemas being repeated within the same OAS docs.

Suggestion

Instead, these schemas should be refactored into /components/schemas.

Use Cases

The OAS document may be more compact and have increased readability as the filter schemas will not be repeated. Furthermore, the generated client-side code may also benefit similarly.

Examples

(Taken from: #4290 (comment))

{
  "TodoFields": {
    "title": "TodoFields",
    "type": "object",
    "properties": {
      "id": {
        "type": "boolean"
      }
     // ...
    }
  },
  "TodoFilter": {
    "title": "TodoFilter",
    "type": "object",
    "properties": {
      "where": {
        "type": "object"
      },
      "fields": {
        "$ref": "#/components/schemas/TodoFields"
      },
      "offset": {
        "minimum": 0,
        "type": "integer",
        "format": "int32"
      },
      "limit": {
        "minimum": 1,
        "type": "integer",
        "format": "int32",
        "example": 100
      },
      "skip": {
        "minimum": 0,
        "type": "integer",
        "format": "int32"
      },
      "order": {
        "type": "array",
        "items": {
          "type": "string"
        },
        "description": ""
      },
      "include": {
        "type": "array",
        "items": {
          "$ref": "#/components/schemas/Include"
        },
        "description": ""
      }
    }
  }

Acceptance criteria

TBD - will be filled by the team.

[dougal83]

@bajtos Here is a draft gist. I need to run code against samples and write tests(*sigh).

Where would be the best to place this code and where to inject it's functionality? I'll put into PR for review pending your feedback.

[jannyHou]

@dougal83 commented in #4290 (comment) :)

[bajtos]

After we land feat(rest): add openapi schema consolidation #4365, I'd like to start the process of deprecating getModelSchemaRef and reworking both our existing code and CLI templates to leverage the new schema consolidation:

• Introduce getModelSchema similar to getModelSchemaRef (see src/controller-spec.ts)
• Rework our controller templates to use getModelSchema instead of getModelSchemaRef
• Rework controllers inside /examples to use getModelSchema
• Soft-deprecate getModelSchemaRef in our documentation (both /docs files and the tsdoc comment)
• Update https://github.com/strongloop/loopback4-example-shopping to use getModelSchema

Considering the scope of that work, I think it may be better to open a follow-up issue.

Thoughts?

[dhmlau]

Closing as done. Opened #5791 as follow up issue.