OpenAPI generates AdditionalProperties field twice

Question

I am generating Swagger client via the OpenAPI but getting an error for additionalProperties as it was defined twice.

The json schema was generated from FastEndpoints project, I tried to add schema filter configuration to disallow the AdditionalPropertiesAllowed - yet no luck.

I'm trying to understand how do we configure the additionalProperties to appear only once in the json schema:

UPDATE:

The issue that I encountered on the generated json schema with additionalProperties defined twice is when I try to generate a CSharpClient through json the client throws an error with additionalProperties defined twice in the model.

Answer 1

You could try experimenting with DocumentSettings like below:

builder.Services
   .AddFastEndpoints()
   .SwaggerDocument(c => c.DocumentSettings = docSettings =>
   {
       docSettings.PostProcess = doc =>
       {
           foreach (var definition in doc.Definitions)
           {
               definition.Value.AdditionalPropertiesSchema = null;
               // and/or 
               definition.Value.AllowAdditionalProperties = false;
           }
       };
   });

It caused additionalProperties to disappear. So maybe it's worth taking a look.

Original answer

This is because in new C# projects, there are nullable reference types (NRTs) turned on by default. Go to your .csproj file and see that you will have set:

<Nullable>enable</Nullable>

And this will cause Swagger to generate these properties.

If you would disable NRTs, like below:

<Nullable>disable</Nullable>

Then Swagger would generate just "additionalProperties": false.

And the reason there are multiple "additionalProperties" properties, is that this is just applicable for every object, and so Swagger generates this information for each object. Not once.