[REQ][csharp-netcore] Support nullable value types

[mlhDevelopment]

Is your feature request related to a problem? Please describe.

.net core v8 introduced nullable value types. If a value is returned as null:

{
    "age": null
}

or explicit undefined:

{
    "age": undefined
}

or missing undefined ({ }) then openapi-generator will set that value to the default for the type. This is appropriate for reference types but introduces ambiguity for value types. E.g. If the age of the cheese is within the past year, the API may response { "age": 0 } but if the age is unknown or not applicable, { } the value of age will be set to 0 in both scenarios.

Describe the solution you'd like

Using the test case below,

Requested State: In OptionalPayload.cs, the property Age is of datatype int?

Current State: In OptionalPayload.cs, the property Age is of datatype int

Regression Scenario: In RequiredPayload.cs, the property Age is of datatype int and should remain int

Describe alternatives you've considered

• Stop using openapi-generator
• Manually editing all openapi-generator output

Additional context

Consider the following YML:

openapi: 3.0.3
info:
  title: Sample API
  version: 1.0.0
  description: Test optional primitive
servers:
  - url: https://example.com/api/v1
    description: Fake service
paths:
  /optional:
    get:
      summary: Get an optional integer value
      operationId: getOptionalAge
      responses:
        "200":
          description: Successful optional integer value
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/OptionalPayload"
  /required:
    get:
      summary: Get a required integer value
      operationId: getRequiredAge
      responses:
        "200":
          description: Successful required integer value
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/RequiredPayload"
components:
  schemas:
    OptionalPayload:
      type: object
      properties:
        age:
          type: integer
          description: Optional Age
    RequiredPayload:
      type: object
      properties:
        age:
          type: integer
          description: Required Age
      required:
      - age

Using CLI generator v2.19.1 (@openapitools/openapi-generator-cli@2.19.1) with the following:

npx @openapitools/openapi-generator-cli generate -i .\sample.yml -g csharp -o .\output --skip-operation-example --enable-post-process-file -p targetFramework=net8.0 -p library=httpclient

The property Age in OptionalPayload.cs should be of type int? and be set to null if received the payload { }

[devhl-labs]

Consider migrating to generichost. It does not have this issue and uses HttpClient and System.Text.Json

[wing328]

did you try enabling the rule SET_PRIMITIVE_TYPES_TO_NULLABLE in openapi normalizer?

ref: https://github.com/openapitools/openapi-generator/blob/master/docs/customization.md#openapi-normalizer

[mlhDevelopment]

@devhl-labs I tried generichost, I get the error "Each parameter in the deserialization constructor on type..." every time. See my reproduction code at https://github.com/mlhDevelopment/openapi-generator-21140.

[I should note that I'm using my code as the client and only using OpenApi Generator for the models]

@wing328 is SET_PRIMITIVE_TYPES_TO_NULLABLE available with the node.js CLI or do I need to use the run the jar directly? And is that with HttpClient or generichost ?

Thanks for your responses and maintenance work.

[devhl-labs]

@mlhDevelopment Please provide the yaml, the config you used to generate the code, and the json that is failing to deserialize.

[mlhDevelopment]

Sure, it is in that repo:

• sample.yml is a sample yaml
• {"age":null} is one of the examples that doesn't work, as seen in Program.cs
• Configuration as seen in generate.ps1 is npx @openapitools/openapi-generator-cli generate -i sample.yml -g csharp -o generatorOutput --skip-operation-example --package-name MyNamespace --model-package MySubset --enable-post-process-file -p targetFramework=net8.0 -p library=generichost

[wing328]

SET_PRIMITIVE_TYPES_TO_NULLABLE available with the node.js CLI or do I need to use the run the jar directly?

yes

And is that with HttpClient or generichost ?

that applies to all generators. for example, it turns the following:

          schema:
            type: integer
            format: int64

into

          schema:
            type: integer
            format: int64
            nullable: true

to indicate it's nullable

[devhl-labs]

@mlhDevelopment There are two issues causing generichost to not work. One is that you need to add nullable: true to your yaml, or use the normalizer as wing pointed out. The second issue is that when deserializing, you must use the JsonSerializerOptions.