Add readyOnly/writeOnly support #807

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1. hactar

   added

   kind/featureNew feature.New feature.

   status/triageCollecting information required to triage the issue.Collecting information required to triage the issue.

   on Aug 12, 2025
2. czechboy0 commented on Aug 12, 2025

   

   czechboy0

   on Aug 12, 2025

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   Hi @hactar,

   thanks for filing this. I agree this is an interesting question and I'm not sure I have a solution right now. Generating all schemas twice seems like a step too far, but I also want us to stay faithful to the spec.

   Do you know what other typesafe language generators do?
3. czechboy0

   added

   area/generatorAffects: plugin, CLI, config file.Affects: plugin, CLI, config file.

   and removed

   status/triageCollecting information required to triage the issue.Collecting information required to triage the issue.

   on Aug 12, 2025
4. hactar commented on Aug 12, 2025

   

   hactar

   on Aug 12, 2025

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   Do you know what other typesafe language generators do?

   While I was googling for information on readOnly and writeOnly, I stumbled across this discussion - a different framework with the same issue. Maybe that discussion is useful input. OpenAPITools/openapi-generator#4190

   Personally I have not worked with a framework that has this available yet, our back team and our client team are trying to clean up an API we use where as a workaround we currently send "0" - and other meaningless values such as creation dates that are ignored by the server during POST as the server is supposed to generate those - to the server during the POSTs, but we need those values to be required during GET. It's messy and while researching of how to solve this via openapi, readOnly and writeOnly were mentioned as the solution to that problem, which makes sense I'd say.
5. czechboy0 commented on Aug 12, 2025

   

   czechboy0

   on Aug 12, 2025

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   A manual way, which I've generally used, is to define separate types for POSTs (creation) and GETs (fetching). For example, unique IDs are often assigned by the server, so it shouldn't need to be in the POST at all.

   For example, check out this example of "*Request" types: https://github.com/swiftlang/swift-server-todos-tutorial/blob/0f7b57bd180ff3b3ca620fdda65141712d941040/Completed/Sources/SwiftServerTodos/openapi.yaml#L100

   In a way, readOnly/writeOnly are just a first class way to represent this coupling of two related schemas.
6. ManuW commented on Nov 9, 2025

   

   ManuW

   on Nov 9, 2025

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   Do you know what other typesafe language generators do?

   We use readOnly and writeOnly in our OpenAPI files and a lot of generators / tools do not support this. But some do support this. I have here two examples:

   Modified Pet Store

   My modified pet store example :

   ...
   components:
     schemas:
       Pet:
         type: object
         required:
           - id
           - name
         properties:
           id:
             type: integer
             format: int64
             readOnly: true
           name:
             type: string
           secret:
             type: string
             writeOnly: true
   ...
   

   Generator Hey API

   Hey API generates two types: Pet and PetWritable.

   Generated TypeScript code:

   ...
   export type Pet = {
       readonly id: number;
       name: string;
   };
   
   ...
   
   export type PetWritable = {
       name: string;
       secret?: string;
   };
   ...
   

   Generator typescript-fetch (OpenAPI Generator)

   The generator typescript-fetch from the OpenAPI Generator uses a different approach. In short, there is a PetToWeb and PetFromWeb functions that handles the writeOnly and readOnly fields.

   Generated code example:

   export interface Pet {
       readonly id: number;
       name: string;
       secret?: string;
   }
   
   /**
    * Check if a given object implements the Pet interface.
    */
   export function instanceOfPet(value: object): value is Pet {
       if (!('id' in value) || value['id'] === undefined) return false;
       if (!('name' in value) || value['name'] === undefined) return false;
       return true;
   }
   
   export function PetFromJSON(json: any): Pet {
       return PetFromJSONTyped(json, false);
   }
   
   export function PetFromJSONTyped(json: any, ignoreDiscriminator: boolean): Pet {
       if (json == null) {
           return json;
       }
       return {
           
           'id': json['id'],
           'name': json['name'],
           'secret': json['secret'] == null ? undefined : json['secret'],
       };
   }
   
   export function PetToJSON(json: any): Pet {
       return PetToJSONTyped(json, false);
   }
   
   export function PetToJSONTyped(value?: Omit<Pet, 'id'> | null, ignoreDiscriminator: boolean = false): any {
       if (value == null) {
           return value;
       }
   
       return {
           'name': value['name'],
           'secret': value['secret'],
       };
   }