Optional INT parameter in Web API Attribute Routing

Question

I'm trying to create an API method in an ASP.NET Core app that may or may not receive an integer input parameter. I have the following code but getting an error with this. What am I doing wrong?

// GET: api/mycontroller/{id}
[HttpGet("id:int?")]
public IActionResult Get(int id = 0)
{
   // Some logic here...
}

Here's the error I'm getting:

Not overly familiar with asp.net core and don't have a dev. env handy, but I suspect it should be like this: "{id?:int}" whereby you are indicating that id is optional and the type is int. So you are missing the { and } and also the ? is in the wrong place as far as I can tell. — Stephen Byrne
– Stephen Byrne, Commented Jun 29, 2016 at 21:07
According to Microsoft documentation, mine is the correct syntax: asp.net/web-api/overview/web-api-routing-and-actions/… — Sam
– Sam, Commented Jun 29, 2016 at 21:13
Yes, I see, however the problem is for sure the missing { and }, because I just tested it and it works fine with { and } but without them I see the same error. So it should be "{id:int?}...otherwise "id:int?" is being treated as a literal string, not a route template. — Stephen Byrne
– Stephen Byrne, Commented Jun 29, 2016 at 21:19

Stephen Byrne · Accepted Answer · 2016-06-29 21:26:15Z

2

"id:int?" is not a valid route template, it's just a string literal (like as if you expected the Request Url to literally look like http://server/api/MyController/id:int? which is not allowed. Funnily enough, that's only because of the ? character; if you removed that then the literal would be allowed (even though it's useless).

Whereas "{id:int?}" is a proper route template and will work correctly, i.e. the Url will look like http://server/api/MyController/42 or http://myserver/api/MyController/ which will give the default value

So the method should be like this:

// GET: api/mycontroller/{id}
[HttpGet("{id:int?}")]
public IActionResult Get(int id = 0)
{
   // Some logic here...
}

answered Jun 29, 2016 at 21:26

Stephen Byrne

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