Added Explode and Style to SwaggerParameter

[aberus]

Pull Request

The issue or feature being addressed

It is currently not possible to set Explode and Style on the parameter.

Details on the issue fix or feature implementation

Added bool Explode and string Style with backing properties bool? ExplodeFlag and Microsoft.OpenApi.Models.ParameterStyle? ParameterStyle respectively. AnnotationsParameterFilter applies these two properties if set.

[martincostello]

Could you add at least one integration/verification test that shows the rendered effect of the new properties in an OpenAPI document please?

[jgarciadelanoceda]

This could close the issue #2248

[jgarciadelanoceda]

@aberus, are you planning to continue with this PR?, because I find it interesting :). I also will like to add the required parameters to solve the issue #2115(That's why I contact you first, to avoid conflicts between us)

[martincostello]

@aberus Thanks for responding to the review suggestions. This still needs tests before we can merge it though.

[aberus]

@martincostello I plan to add tests. But also I think that generation need to be changed, to support these two scenarions.

The default ASP.NET model binding parses the query ?sizes=a,b,c,d as a parameter of type string.

[HttpGet("Products")]
public IActionResult Get([FromQuery(Name = "sizes")][SwaggerParameter(Explode = false)] string sizes)
{
    return Ok();
}

The custom model binding ([CommaSeparated]) mentioned in #2248 can be mapped to a collection;

[HttpGet("Products")]
public IActionResult Get([FromQuery(Name = "sizes")][SwaggerParameter(Explode = false)][CommaSeparated] IEnumerable<string> sizes)
{
    return Ok();
}

Both of these scenarios should produce this:

paths:
  /Products:
    get:
      parameters:
        - name: sizes
          in: query
          style: form
          explode: false
          schema:
            type: array
            items:
              type: string
      responses:
        '200':
          description: Success

Let me know, what do you think?

[martincostello]

How would you propose adding metadata (i.e. an attribute) indicating that the parameters should be treated that way to both ASP.NET Core and Swashbuckle? The issue points to a Stack Overflow answer, which points to a blog post, which mentions a custom implementation of ASP.NET Core model binding. We wouldn't want to be shipping model binders in Swashbuckle, because that's not specific to OpenAPI.

[aberus]

My suggestion in first example is that a non-collection parameter combination with explode set to false, should generate an array in the OpenAPI specification.
Second example show how currently works (with this change) if explode set to false, but external library need to used to work property. I didn't mean that some external library needs to be added, just that this scenario also needs to be supported if someone wants to use it with external library.