Custom `type` is not retained as type, but rewritten as `allOf: - $ref: ...` breaking `nullable: true` spec in `@ApiProperty`

[Gregory Orton]

Is there an existing issue for this?

• I have searched the existing issues

Current behavior

Custom type is not retained as type, but rewritten as allOf: - $ref: ... breaking nullable: true spec in @ApiProperty

In @ApiProperty when using something like:

@ApiProperty({ nullable: true, type: MyCustomDto })
readonly myVar: MyCustomDto | null;
...

the rendered openapi.yaml is like:

myVar:
  nullable: true
  allOf:
     - $ref: "#/components/schemas/MyCustomDto"

tools like Redoc.ly then start to throw errors:

Minimum reproduction code

https://nothing.com

Steps to reproduce

see above

Expected behavior

myVar:
  type: object
  properties:
    id:
      type: integer

Package version

7.3.0

NestJS version

10.3.3

Node.js version

20

In which operating systems have you tested?

• macOS
• Windows
• Linux

Other

maybe related: #2645
maybe related: #2646

[Kamil Mysliwiec]

Would you like to create a PR for this issue?

[Gregory Orton]

Sure, but I don't know what the solution would be here -

what should the value of type be? Would we need to put the custom DTO into a schemas and then reference it?

[Gregory Orton]

One solution looks like:

myVar:
  nullable: true
  allOf:
    - $ref: "#/components/schemas/MyCustomDto"
    - type: object

I will test with redoc.ly to see if it's acceptable. If it is, then I think we can just add this type to the output for the custom type.

[Gregory Orton]

The only think redoc.ly will accept is:

myVar:
  nullable: true
  type: object
  allOf:
    - $ref: "#/components/schemas/MyCustomDto"

so it seems like an easy fix

[Clinton Blackburn]

Here is the source of our woes:

swagger/lib/services/schema-object-factory.ts

Lines 368 to 379 in 5404905

 const keysToRemove = ['type', 'isArray', 'required']; 
 const validMetadataObject = omit(metadata, keysToRemove); 
 const extraMetadataKeys = Object.keys(validMetadataObject); 
  
 if (extraMetadataKeys.length > 0) { 
   return { 
     name: metadata.name || key, 
     required: metadata.required, 
     ...validMetadataObject, 
     allOf: [{ $ref }] 
   } as SchemaObjectMetadata; 
 } 

Extra keys that are not in the set of ['type', 'isArray', 'required'] will result in an allOf instead of a direct $ref. In this case (and #2645), the key is nullable. In my case, it's name.

The list of supported keys needs to be expanded, or removed altogether. I'm not sure which one as I haven't read the OpenAPI spec to any level of detail.