Adding Query String Params to my Swagger Specs

Question

I am using Swashbuckle (swagger for C#) with my Web API. I have several GET End-Points that return lists and I allow the user to add a perpage and page params into the QueryString

Example: http://myapi.com/endpoint/?page=5&perpage=10

I see that swagger does support parameter in 'query' but how do I get Swashbuckle to do it?

---

I mention in one of the comments that I solved my issue by creating a custom attribute to allow me to do what I needed. Below is the code for my solution:

[AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = true)]
public class SwaggerParameterAttribute : Attribute
{
    public SwaggerParameterAttribute(string name, string description)
    {
        Name = name;
        Description = description;
    }

    public string Name { get; private set; }
    public Type DataType { get; set; }
    public string ParameterType { get; set; }
    public string Description { get; private set; }
    public bool Required { get; set; } = false;
}

Register the Attribute with the Swagger Config:

GlobalConfiguration.Configuration 
    .EnableSwagger(c =>
        {
            c.OperationFilter<SwaggerParametersAttributeHandler>();
        });

Then add this attribute to your methods:

[SwaggerParameter("page", "Page number to display", DataType = typeof(Int32), ParameterType = ParameterType.inQuery)]
[SwaggerParameter("perpage","Items to display per page", DataType = typeof(Int32), ParameterType = ParameterType.inQuery)]

Answer 1

You can achieve that quite easily. Suppose you have an ItemsController with an action like this:

[Route("/api/items/{id}")]
public IHttpActionResult Get(int id, int? page = null, int? perpage = null)
{
   // some relevant code
   return Ok();
}

Swashbuckle will generate this specification (only showing relevant part):

"paths":{  
  "/api/items/{id}":{  
     "get":{  
        "parameters":[  
           {  
              "name":"id",
              "in":"path",
              "required":true,
              "type":"integer",
              "format":"int32"
           },
           {  
              "name":"page",
              "in":"query",
              "required":false,
              "type":"integer",
              "format":"int32"
           },
           {  
              "name":"limit",
              "in":"query",
              "required":false,
              "type":"integer",
              "format":"int32"
           }
        ]
     }
  }

When you want page and perpage to be required, just make the parameters not nullable.

Answer 2

Here is a summary of the steps required (ASP.Net Core 2.1, Swashbuckle.AspNetCore v4.0.1) for the Attribute method. I needed a parameter starting with "$" so optional parameters were not an option!

SwaggerParameterAttribute.cs

     [AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = true)]
     public class SwaggerParameterAttribute : Attribute
     {
         public SwaggerParameterAttribute(string name, string description)
        {
            Name = name;
            Description = description;
        }

        public string Name { get; private set; }
        public string DataType { get; set; }
        public string ParameterType { get; set; }
        public string Description { get; private set; }
        public bool Required { get; set; } = false;
    }

SwaggerParameterAttributeFilter.cs

using Swashbuckle.AspNetCore.Swagger;
using Swashbuckle.AspNetCore.SwaggerGen;
using System.Linq;
public class SwaggerParameterAttributeFilter : IOperationFilter
{
    public void Apply(Operation operation, OperationFilterContext context)
    {
        var attributes = context.MethodInfo.DeclaringType.GetCustomAttributes(true)
            .Union(context.MethodInfo.GetCustomAttributes(true))
            .OfType<SwaggerParameterAttribute>();

        foreach (var attribute in attributes)
            operation.Parameters.Add(new NonBodyParameter
            {
                Name = attribute.Name,
                Description = attribute.Description,
                In = attribute.ParameterType,
                Required = attribute.Required,
                Type = attribute.DataType
            });              
    }
}

add this in Startup.ConfigureServices

 using Swashbuckle.AspNetCore.Swagger;
 services.AddSwaggerGen(c =>
 {
      c.OperationFilter<SwaggerParameterAttributeFilter>();
      c.SwaggerDoc("v1.0", new Info { Title = "My API", Version = "v1.0" });
 });

and use like this:

[SwaggerParameter("$top", "Odata Top parameter", DataType = "integer", ParameterType ="query")]

DataTypes can be: integer, string, boolean

ParameterTypes: can be path, body, query

Answer 3

There's some comments here regarding missing information on the SwaggerParametersAttributeHandler. It is an operation filter to help you determine what to do to your attributes.

Here's an example handler I used that allows me to override nullable parameters' required fields using the SwaggerParameterAttribute.

public class RequiredParameterOverrideOperationFilter : IOperationFilter
{
    public void Apply(Operation operation, SchemaRegistry schemaRegistry, ApiDescription apiDescription)
    {
        // Get all SwaggerParameterAttributes on the method
        var attributes = apiDescription.ActionDescriptor.GetCustomAttributes<SwaggerParameterAttribute>();

        if (operation.parameters == null)
        {
            operation.parameters = new List<Parameter>();
        }

        // For each attribute found, find the operation parameter (this is where Swagger looks to generate the Swagger doc)
        // Override the required fields based on the attribute's required field
        foreach (var attribute in attributes)
        {
            var referencingOperationParameter = operation.parameters.FirstOrDefault(p => p.name == attribute.Name);

            if (referencingOperationParameter != null)
            {
                referencingOperationParameter.required = attribute.Required;
            }
        }
    }
}