IOpenApiDocumentTransformer cannot modify components.Schemas since it's null

[dnv-kimbell]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When running IOpenApiDocumentTransformer, it would be logical to have the ability to modify the OpenApiDocument.Components.Schemas to make any adjustments. The OpenApiDocument.Components is null.

aspnetcore/src/OpenApi/src/Services/OpenApiDocumentService.cs

Lines 100 to 106 in 049814c

	for (var i = 0; i < _options.DocumentTransformers.Count; i++)
	{
	var transformer = _options.DocumentTransformers[i];
	await transformer.TransformAsync(document, documentTransformerContext, cancellationToken);
	}
	// Move duplicated JSON schemas to the global components.schemas object and map references after all transformers have run.
	await _schemaReferenceTransformer.TransformAsync(document, documentTransformerContext, cancellationToken);

The await _schemaReferenceTransformer.TransformAsync(document, documentTransformerContext, cancellationToken) populates the Components.Schemas, but that happens after the document transformers are run.

Expected Behavior

It should be possible to modify Components.Schemas in the IOpenApiDocumentTransformer

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

.NET 9 RC2

Anything else?

No response

[captainsafia]

@dnv-kimbell This is expected behavior. If you are trying to make schema-level customizations, the IOpenApiSchemaTransformer API is the one that you want to use.

What are you trying to do?

[dnv-kimbell]

The reason why I started exploring this was to see if I could create a workaround for polymorphic types. I can't see how the information provided by the current Microsoft implementation can give me enough information to generate C# classes.

There may also be other scenarios where one would want to look at the total list of schemas rather than each one individually. Based on the name of the transformer, it's not unreasonable to expect that you get a complete document, not just parts of it.

Since this code is part of the yearly release schedule, we have to wait another year for any significant changes. If we had access to information, it would be possible for us to create workarounds until the Microsoft implementation is updated.