Support options for setting callback used to generated reference IDs in OpenAPI

[captainsafia]

Background and Motivation

The OpenAPI implementation generates reference IDs for schemas that are duplicated across the OpenAPI document. By default, a unique identifier is generated for the schema using a combination of the schema itself and the type associated with the schema. At times, it might be necessary for users to override our default behavior with their own reference ID generation function.

Proposed API

namespace Microsoft.AspNetCore.OpenApi;

public sealed class OpenApiOptions
{
+    public Func<JsonTypeInfo, string?> CreateSchemaReferenceId { get; set; }
}

Usage Examples

var builder = WebApplication.CreateBuilder();

builder.Services.AddOpenApi(options =>
{
	CreateSchemaReferenceId = (jsonTypeInfo) => $"My{jsonTypeInfo.Type.Name}",
});
builder.Services.AddOpenApi(options =>
{
	// Returning null means that all schemas will be inlined, can also be used to
	// conditional inline a schema
	CreateSchemaReferenceId = (jsonTypeInfo) => null,
});

var app = builder.Build();

app.MapOpenApi();

app.MapGet("/", () => "Hello world!");

app.Run();

Alternative Designs

Instead of specifying custom schema IDs via a callback, we could support a custom attribute on types that would allow users to set reference IDs for the types they care about. For example:

[SchemaReferenceId("some-name-here")]
public class Todo { }

Risks

Exposing an option for customizing the way reference IDs are created adds additional burden onto the user to ensure that the callback they provide will generate unique and accurate reference IDs for all the types that are used in their application.

[michael-wolfenden]

@captainsafia In my api's I like to nest the request / responses objects within the class containing the endpoint mapping as well as the implementation.

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddOpenApi();

var app = builder.Build();
app.MapOpenApi();

CreateArticle.MapEndpoint(app);
UpdateArticle.MapEndpoint(app);

app.Run();

public class CreateArticle
{
    public static RouteHandlerBuilder MapEndpoint(IEndpointRouteBuilder endpoints) =>
        endpoints.MapPost("/articles", async (Request request) => { });

    public record Request(string title);
}

public class UpdateArticle
{
    public static RouteHandlerBuilder MapEndpoint(IEndpointRouteBuilder endpoints) =>
        endpoints.MapPost("/articles/{id}", async (string id, Request request) => { });

    public record Request(string title, string description);
}

However this results in schema's named Request and Request2.

Would this feature allow me to generate ids like CreateArticleRequest and UpdateArticleRequest based on the type, like squashbuckle's CustsomSchemaIds option?

[captainsafia]

In my api's I like to nest the request / responses objects within the class containing the endpoint mapping as well as the implementation.

Oh! I really like this organization structure.

Would this feature allow me to generate ids like CreateArticleRequest and UpdateArticleRequest based on the type, like squashbuckle's CustsomSchemaIds option?

Yes -- it would! I'm actually hoping to take this API through review (ref) tomorrow. Do you have any thoughts on the shape I am currently proposing for it that we should consider as part of the review?

[michael-wolfenden]

Awesome @captainsafia, your initial suggestion makes the most sense to me

public Func<Type, OpenApiSchema, string> CreateReferenceId { get; set; }

[captainsafia]

@michael-wolfenden I ended up making a few changes to the API ahead of today's API review after I started implementing it. You should still be able to achieve the desired result but the shape is a little different now.

[amcasey]

[API Review]

• What happens if CreateSchemaReferenceId returns the same value twice?
  • We have centralized de-duping that tacks on sequential integers
  • This is a way users can make that de-duping less likely by more fully qualifying their names
• Why is the return value nullable?
  • Can return null to prevent referencing (i.e. force inlining)
  • People might plausibly think it means "use the default schema name"
• The default implementation isn't just trivially returning the name
• Options:
  • 1. Make signature Func<JsonTypeInfo, string>, always require returning a value
  • 1. Keep signature Func<JsonTypeInfo, string?> and say that null means we call the framework default
  • 1. Keep the signature as it is and provide the framework default as an option the user can invoke
  • 1. Separate filtering from naming with an out param

CreateSchemaReferenceId = (type) => {
  - if (type ...)
      - return type.FullName;
  - else
      - return OpenApiOptions.CreateDefaultSchemaReferenceId(type);
}

• CreateSchemaReferenceId is non-optional in the API but has a default value

namespace Microsoft.AspNetCore.OpenApi;

public sealed class OpenApiOptions
{
+    public static string? CreateDefaultSchemaReferenceId(JsonTypeInfo jsonTypeInfo);
+    public Func<JsonTypeInfo, string?> CreateSchemaReferenceId { get; set; }
}

API Approved!

[bkoelman]

This looks great. Though I find returning null to inline the schema kinda odd. What's the use case for inlining?

Would this also enable to specify the name of the discriminator property? I'm asking because we have a use case where it must be one of the model properties (the JSON:API spec we implement requires this). Example:

"dataInResponse": {
  "required": [
    "type"
  ],
  "type": "object",
  "properties": {
    "type": {
      "minLength": 1,
      "type": "string"
    }
  },
  "additionalProperties": false,
  "discriminator": {
    "propertyName": "type",
    "mapping": {
      "people": "#/components/schemas/personDataInResponse",
      "tags": "#/components/schemas/tagDataInResponse",
      "todoItems": "#/components/schemas/todoItemDataInResponse"
    }
  },
  "x-abstract": true
}

In the example above, we must ensure that:

• discriminator.propertyName is type (the model class doesn't actually contain a Type property, a concern for later)
• mapping values must be people/tags/todoItems (they do not match the class names)
• I'm assuming this issue enables to set personDataInResponse/tagDataInResponse/todoItemDataInResponse

For completeness, one of the derived types looks like this (I've left out extra properties in both snippets for brevity):

"personDataInResponse": {
  "allOf": [
    {
      "$ref": "#/components/schemas/dataInResponse"
    },
    {
      "required": [
        "id"
      ],
      "type": "object",
      "properties": {
        "id": {
          "minLength": 1,
          "type": "string"
        }
      },
      "additionalProperties": false
    }
  ],
  "additionalProperties": false
},