Swashbuckle - Free form query parameters

I’m creating an api where an arbitrary number of query parameters can be added.

The API looks something like this:

GET /api/example?param1=value1&param2=value2&param3=value3

By default when Swashbuckle generates the Swagger UI it only includes parameters that are explicitly defined at the action method level.

Luckily the Open API spec supports this starting from version 3 through ‘free form query parameters’.

At the spec level this looks like this:

	openapi: 3.0.1
	paths:
	/example:
	get:
	parameters:
	- in: query
	name: params
	schema:
	type: object
	additionalProperties:
	type: string
	# `style: form` and `explode: true` is the default serialization method
	# for query parameters, so these keywords can be omitted
	style: form
	explode: true

view raw openapi.yaml hosted with ❤ by GitHub

To achieve this using Swashbuckle you can use an operation filter:

	public class QueryParametersFilter : IOperationFilter
	{
	public void Apply(OpenApiOperation operation, OperationFilterContext context)
	{
	if (!context.MethodInfo.Name.StartsWith("UploadDocument"))
	return;
	operation.Parameters.Add(new OpenApiParameter()
	{
	In = ParameterLocation.Query,
	Name = "params",
	Schema = new OpenApiSchema()
	{
	Type = "object",
	AdditionalProperties = new OpenApiSchema()
	{
	Type = "string"
	}
	},
	Style = ParameterStyle.Form,
	Explode = true,
	});
	}
	}

view raw QueryParametersFilter.cs hosted with ❤ by GitHub

This will generate the following UI: