Error failed to add operation for get api v1 connections

Issue Description

Swagger Open API documentation gives the below error in .NET Core API etc.

“Failed to load API definition. Fetch error undefined /swagger/v1/swagger.json”

It is also observed that Swagger API documentation/description works on ‘localhost’ i.e locally but when it runs in publish mode i.e hosted on IIS or Cloud Server, produces the error like “Failed to load API definition” with undefined/swagger/v1/swagger.json error.

Resolution

Before applying this fix, I would recommend you to validate the swagger implementation with the below article,

• ASP.NET Core 3.1 or 5.0 – Add Swagger OpenAPI V3.0 specification documentation

• ASP.NET Core 2.2- Add Swagger v2.0 API documentation

Please make sure you verify the below points steps,

Resolution 1

Swagger Document is defined with proper Title and Version details, as both are required parameters.

Resolution 2

Please make sure the API doesn’t contain any conflicting action. Conflicting action could be using the same routes. To be on the safer side, you can very much use the below flag to control that behavior,

c.ResolveConflictingActions(x => x.First());

Resolution 3

Please make sure all controller methods are attributed with proper HTTP attributes Example- HttpGET or HttpPost etc. Missing this attribute could cause the error.

If the issue still persists then please apply the below fix to resolve the issue.

Resolution 5

Please check if the hosting server allows CORS request processing. Also, its important swagger UI-related resources like CSS or stylesheets are accessible from your server.

Resolution 6

Please, note that Swagger JSON will be exposed at the following route as per default behavior.

"/swagger/{documentName}/swagger.json". 

If you are using a custom route or prefix, then the route MUST include the {documentName} parameter.

To fix the issue, please update the UseSwagger() as below,

app.UseSwagger(c =>
             {
                c.RouteTemplate = "<custom-name>/swagger/{documentName}/swagger.json";
             });

Example,

 c.RouteTemplate = "MyTestService/swagger/{documentName}/swagger.json";  

The above changes also need to be reflected in SwaggerUI middleware. Please update the UseSwaggerUI method will be as follows,

app.UseSwaggerUI(c =>
             {
                 c.SwaggerEndpoint("/<custom-name>/swagger/v1/swagger.json", "TestService");
             });

Example:

 app.UseSwaggerUI(c =>
             {
          c.SwaggerEndpoint("/MyTestService/swagger/v1/swagger.json", "TestService");
             }); 

Please note that in Swaggerendpoint() method ‘documentName’ value is cases sensitive.

In fact, documentName is case sensitive anywhere else if referenced.

This documentName is generally a Group Name associated with API version

Example: It won’t work for V1 but works for v1.

If using RoutePrefix in API then it can be defined as below,

Example only if using RoutePrefix,

c.RoutePrefix= "MyTestService/swagger"

Here MyTestService is my service name.

Please see below the complete implementation,

Finally, Swagger runs successfully locally and in any hosting environment like IIS or Azure Cloud, etc.

For any other issues, please use google chrome dev tools(FUN F12) or Edge Developer tools to verify the exact error causing the issue. Please verify Console and Network tab to validate the exact erros.

Other References:

Add swagger to ASP.NET Core API in simple 2-3 steps:

• Swagger API Documentation in .NET Core 6 or 3.1

• Add Swagger API documentation to .NET Core 2.2

Did I miss anything else in these resolution steps?

Did the above steps resolve your issue? Please sound off your comments below!

Happy Coding !!

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