Swagger default value for parameter

Question

How do I define default value for property in swagger generated from following API?

public class SearchQuery
{
        public string OrderBy { get; set; }

        [DefaultValue(OrderDirection.Descending)]
        public OrderDirection OrderDirection { get; set; } = OrderDirection.Descending;
}


public IActionResult SearchPendingCases(SearchQuery queryInput);

Swashbuckle generates OrderDirection as required parameter. I would like it to be optional and indicate to client the default value (not sure if swagger supports this).

I don't like making the property type nullable. Is there any other option? Ideally using built in classes...

I use Swashbuckle.AspNetCore - https://learn.microsoft.com/en-us/aspnet/core/tutorials/web-api-help-pages-using-swagger?tabs=visual-studio

Answer 1

I've always set the default on the param itself like this:

public class TestPostController : ApiController
{
    public decimal Get(decimal x = 989898989898989898, decimal y = 1)
    {
        return x * y;
    }
}

Here is how that looks like on the swagger-ui:
http://swashbuckletest.azurewebsites.net/swagger/ui/index#/TestPost/TestPost_Get

UPDATE

Following the discussion on the comments I updated Swagger-Net to read the DefaultValueAttribute via reflection Here is the sample class I'm using:

public class MyTest
{
    [MaxLength(250)]
    [DefaultValue("HelloWorld")]
    public string Name { get; set; }
    public bool IsPassing { get; set; }
}

and here is how the swagger json looks like:

"MyTest": {
  "type": "object",
  "properties": {
    "Name": {
      "default": "HelloWorld",
      "maxLength": 250,
      "type": "string"
    },
    "IsPassing": {
      "type": "boolean"
    }
  },
  "xml": {
    "name": "MyTest"
  }
},

The Source code of Swagger-Net is here:
https://github.com/heldersepu/Swagger-Net

And the source code for the test project is here:
https://github.com/heldersepu/SwashbuckleTest

Answer 2

Setting the default parameter value works like this if you can do it in your controller

// GET api/products
[HttpGet]
public IEnumerable<Product> Get(int count = 50)
{
    Conn mySqlGet = new Conn(_connstring);
    return mySqlGet.ProductList(count);
}

Answer 3

This is applicable for ASP.net MVC5, code is not valid for .Net Core

1- Define a custom attribute as following

public class SwaggerDefaultValueAttribute: Attribute
{
   public SwaggerDefaultValueAttribute(string param, string value)
   {
      Parameter = param;
      Value = value;
   }
   public string Parameter {get; set;}
   public string Value {get; set;}
}

2- Define a Swagger OperationFilter class

public class AddDefaulValue: IOperationFilter
{
   void IOperationFilter.Apply(Operation operation, SchemaRegistry schemaRegistry, ApiDescription apiDescription)
   {
      if (operation.parameters == null || !operation.parameters.Any())
      {
         return;
      }
      var attributes = apiDescription.GetControllerAndActionAttributes<SwaggerDefaultValueAttribute>().ToList();

      if (!attributes.Any())
      {
         return;
      }
      
      foreach(var parameter in operation.parameters)
      {
         var attr = attributes.FirstOrDefault(it => it.Parameter == parameter.name);
         if(attr != null)
         {
            parameter.@default = attr.Value;
         }
      }
   } 
}

3- Register the OperationFilter at SwaggerConfig file

c.OperationFilter<AddDefaultValue>();

4- Decorate your controller method with attributes

[SwaggerDefaultValue("param1", "AnyValue")]
public HttpResponseMessage DoSomething(string param1)
{
   return Request.CreateResponse(HttpStatusCode.OK);
}

Answer 4

First approach

According to one of the answers here you should be able to simply add the following to your model although I haven't verified this:

 public class ExternalJobCreateViewModel
{
    ///<example>Bob</example>
    public string CustomFilename { get; set; }
    ...etc

Second approach

In .net 6 I used the following:

public class MyFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {

        if (operation.OperationId.Equals("somecontroller_somepath", StringComparison.OrdinalIgnoreCase))
        {                
            operation.Parameters.Clear();
            operation.Parameters = new List<OpenApiParameter>
            {
                new OpenApiParameter()
                {
                    Name = "document-name",
                    Schema = new OpenApiSchema()
                    {
                        Type = "string",
                    },
                    Example = new Microsoft.OpenApi.Any.OpenApiString("docName1"),
                    In = ParameterLocation.Query
                },
                new OpenApiParameter()
                {
                    Name = "user-email",
                    Schema = new OpenApiSchema()
                    {
                        Type = "string",
                    },
                    Example = new Microsoft.OpenApi.Any.OpenApiString("elvis.presley@somemail.com"),
                    In = ParameterLocation.Query
                },
                new OpenApiParameter()
                {
                    Name = "account-type-id",
                    Schema = new OpenApiSchema()
                    {
                        Type = "string",
                    },
                    Example = new Microsoft.OpenApi.Any.OpenApiString("2"),
                    In = ParameterLocation.Query
                }
            };
        }
    }
}

Then in Program.cs

builder.Services.AddSwaggerGen(options =>
            {
                ... other stuf
                options.OperationFilter<MyFilter>();

3rd Approach

I never used this code so not tested

In .net 6 and Piggybacking off of Sameh's answer...

To use multiple attributes decorate your attribute class like this:

[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public class SwaggerDefaultValueAttribute : Attribute
{
 ... etc

For 6.5.0 of swashbuckle I think it is something like this for properties:

public class AddDefaulValueFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        if (operation.Parameters == null || !operation.Parameters.Any())
        {
            return;
        }
        context.ApiDescription.TryGetMethodInfo(out var x);
        if (x != null)
        {
            return;
        }
        var attributes = x!.GetCustomAttributes<SwaggerDefaultValueAttribute>().ToList();

        if (!attributes.Any())
        {
            return;
        }

        foreach (var parameter in operation.Parameters)
        {
            var attr = attributes.FirstOrDefault(it => it.Parameter == parameter.Name);
            if (attr != null)
            {
                parameter.Schema.Default = new OpenApiString(attr.Value);
            }
        }
    }
}

Since I was trying to use this for body parameters on a multipart message I Had to do something like this but use at your own risk:

public class AddDefaulValueFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        if(operation.RequestBody == null)
        {
            return;
        }
        var keys = operation.RequestBody.Content.Where(val => val.Key == "multipart/form-data").Take(1).ToList();
        if(!keys.Any())
        {
            return;
        }
        var props = keys.FirstOrDefault().Value.Schema.Properties;
        if (props == null || !props.Any())
        {
            return;
        }
        context.ApiDescription.TryGetMethodInfo(out var x);
        if (x == null)
        {
            return;
        }
        var attributes = x!.GetCustomAttributes<SwaggerDefaultValueAttribute>().ToList();

        if (!attributes.Any())
        {
            return;
        }

        foreach (var prop in props)
        {
            var attr = attributes.FirstOrDefault(it => it.Parameter == prop.Key);
            if (attr != null)
            {
                prop.Value.Default = new OpenApiString(attr.Value);
            }
        }
    }
}

Answer 5

In the YAML file, you can define which properties should be required. This example is from a NSwag configuration.

/SearchPendingCases:
    post:
      summary: Search pending cases
      description: Searches for pending cases and orders them
      parameters:
        - in: body
          name: SearchQuery 
          required: true
          schema:
            type: object
            required:
              - OrderBy
              # do not include OrderDirection here because it is optional
            properties:
              OrderBy:
                description: Name of property for ordering
                type: string
                # you can remove the following two lines 
                # if you do not want to check the string length
                minLength: 1    
                maxLength: 100
              OrderDirection:
                description: Optional order direction, default value: Descending
                type: string
                enum: [Ascending, Descending] # valid enum values
                default: Descending           # default value

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