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Why is MVC query parameter being used for the wrong variable?

I have a problem with all my controller endpoints, whenever I use sort and filter as query parameter in a way similar to this example:
[Microsoft.AspNetCore.Mvc.HttpGet,
Microsoft.AspNetCore.Mvc.Route("{tenantId}/archive/retrievals", Name = "getRetrievalList")]
public System.Threading.Tasks.Task<RetrievalListResult> GetRetrievalList([Microsoft.AspNetCore.Mvc.FromQuery] int? limit = null, [Microsoft.AspNetCore.Mvc.FromQuery] int? offset = null, [Microsoft.AspNetCore.Mvc.FromQuery] System.Collections.Generic.IEnumerable<string> sort = null, [Microsoft.AspNetCore.Mvc.FromQuery] System.Collections.Generic.IDictionary<string, string> filter = null)
{
throw new NotImplementedException();
}
It works perfectly fine with these calls:
{{baseUrl}}/:tenantId/archive/retrievals?filter[fields]=Text 01
{{baseUrl}}/:tenantId/archive/retrievals?sort=name&filter[fields]=Text 01
But when I only use sort…
{{baseUrl}}/:tenantId/archive/retrievals?sort=name
...then suddenly both sort and filter variables are filled, creating a false filter parameter.
Any solutions for that?
P.S. using only filter=id results in none of the variables being filled which is as I expect.

For Dictionary targets, model binding looks for matches to parameter_name or property_name. If no match is found, it looks for one of the supported formats without the prefix.
In other words, "sort=name" matches the format of the supported target parameter Dictionary<string, string> named filter.
Therefore, it will also be automatically bound to the filter.
You can specify the prefix to solve the problem.
public IEnumerable<WeatherForecast> Get(
[FromQuery] int? limit = null,
[FromQuery] int? offset = null,
[FromQuery] IEnumerable<string> sort = null,
[FromQuery][Bind(Prefix = "filter")]IDictionary<string, string> filter = null
)

Route based attributes taking the incorrect method when data constraints are applied

I have the following API controller class.
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Routing;
namespace Core31Test.Controllers
{
[ApiController]
[Route("[controller]")]
public class DataController : ControllerBase
{
[HttpGet]
[Route("query/{idr:int?}")]
public string Get(int idr, [FromQuery] int id)
{
var idx = id == 0 ? idr : id;
return $"Value: {idx}";
}
[HttpGet]
[Route("query/{cityr}")]
public string GetByCity(string cityr, [FromQuery] string city)
{
var cityx = string.IsNullOrEmpty(city) ? cityr : city;
return cityx;
}
}
}
When I attempt to query by an id, both the route based path and the query string work. When I attempt to query by city, only the route based path works. The querystring path ends up taking the incorrect path.
For example:
http://localhost:51123/data/query/1
Result: value: 1
http://localhost:51123/data/query?id=1
Result: value: 1
http://localhost:51123/data/query/mycity
Result: mycity
http://localhost:51123/data/query?city=acity
Result: value: 0
In the last case, the incorrect route is being selected. Why is this happening and how can I fix it?
Edit 1
If I modify the route for the GetByCity method to be the one given below, the Get method is still selected. In this case, both methods have an optional route parameter and a querystring. Since the Get route specifies the input is an integer, I do not understand why the GetByCity method is going to that one. What I would like to know is how to make this work.
[Route("query/{cityr?}")]

In the last case, the incorrect route is being selected. Why is this happening and how can I fix it?
No, it's not. The correct and expected route is being selected. Let's take a closer look:
The route is query?city=acity
The available actions are:
query/ + optional int parameter (query/{idr:int?})
query/ + required string parameter ("query/{cityr}")
If you think about it, query/ does not satisfy query/ + required string parameter, as no value for cityr was given, so the correct route is the idr overload since that parameter is optional.

Swagger - Web API - Optional query parameters

[HttpGet]
[Route("students")]
[SwaggerOperation(Tags = new[] { "Student" })]
[SwaggerResponse(HttpStatusCode.OK, Type = typeof(ResponseModel<IList<Student>>))]
[SwaggerResponseExample(HttpStatusCode.OK, typeof(StudentResponseExample))]
[SwaggerResponse(HttpStatusCode.InternalServerError)]
public IHttpActionResult SearchStudent()
{
IDictionary<string, string> searchParams = null;
searchParams = ControllerContext.GetQueryStrings();
.
.
.
}
The above API has three optional parameters which will be pass as query string
SyncDate - Long
OffSet - int
Limit - int
There is no option for user to enter these optional query parameters in swagger UI. Please guide me to implement the optional query parameters.
I am using swashbuckle and I prefer to use annotations rather than having a lengthy comment section over each API method for swagger functionalities.
I referred the following Adding Query String Params to my Swagger Specs and created the SwaggerParameterAttribute class in Filters folder of Web API and when trying to add the OperationFilter in GlobalConfiguration.Configuration
.EnableSwagger as given, it throws type or the namespace name SwaggerParametersAttributeHandler could not be found. I even added the Filters folder namespace but still the error exists.
Please guide on how to implement the optional query parameters in swagger

The way Swagger works it pulls out parameters based on your signature of Action i.e parameters to your Action, but here you are getting these value from ControllerContext which obviously Swagger will never be aware of.
So You need to change the signature of the Action and pass your parameters there.
They will be treated as optional if you make them of nullable type -
[HttpGet]
[Route("students")]
[SwaggerOperation(Tags = new[] { "Student" })]
[SwaggerResponse(HttpStatusCode.OK, Type = typeof(ResponseModel<IList<Student>>))]
[SwaggerResponseExample(HttpStatusCode.OK, typeof(StudentResponseExample))]
[SwaggerResponse(HttpStatusCode.InternalServerError)]
public IHttpActionResult SearchStudent(long? SyncDate = null,int? OffSet = null,int? Limit = null)
{
// Use the variables here
.
.
.
}

This worked for me:
[System.Web.Http.HttpGet]
[Route("api/DoStuff/{reqParam}")]
[Route("api/DoStuff/{reqParam}/{optParam1:alpha?}/{optParam2:datetime?}")]
public string Get(string reqParam, string optParam1= "", string optParam2= "")
It did create two sections in my Swagger UI but that works for me.

Optional Parameters in Web Api Attribute Routing

I want to handle POST of the following API-Call:
/v1/location/deviceid/appid
Additional Parameter are coming from the Post-Body.
This all works fine for me. Now I wnat to extend my code by allowing "deviceid" and/or "appid" and/or BodyData to be null:
/v1/location/deviceid
/v1/location/appid
/v1/location/
These 3 URLs should responded by the same route.
My first approach (BodyData required):
[Route("v1/location/{deviceid}/{appid}", Name = "AddNewLocation")]
public location_fromuser Post(string deviceid = null, string appid = null, [FromBody] location_fromuser BodyData)
{
return repository.AddNewLocation(deviceid, appid, BodyData);
}
This does not work and returns a compile error:
"optional Parameters must be at the end"
Next try:
[Route("v1/location/{deviceid}/{appid}", Name = "AddNewLocation")]
public location_fromuser Post([FromBody] location_fromuser BodyData, string deviceid = null, string appid = null)
Now my function AddNewLocation() get always an BodyData=null - even if the call send the Body.
Finally I set all 3 Parameter optional:
[Route("v1/location/{deviceid}/{appid}", Name = "AddNewLocation")]
public location_fromuser Post(string deviceid = null, string appid = null, [FromBody location_fromuser BodyData = null)
Don´t work:
Optional parameter BodyData is not supported by FormatterParameterBinding.
Why do I want a solution with optional Parameters? My Controller handles just the "adding of a new Location" via a POST.
I want to send on wrong data my own exceptions or error messages. Even if the call has missing values. In this case I want to be able to decide to throw an exception or Setting Defaults by my code.

For an incoming request like /v1/location/1234, as you can imagine it would be difficult for Web API to automatically figure out if the value of the segment corresponding to '1234' is related to appid and not to deviceid.
I think you should change your route template to be like
[Route("v1/location/{deviceOrAppid?}", Name = "AddNewLocation")] and then parse the deiveOrAppid to figure out the type of id.
Also you need to make the segments in the route template itself optional otherwise the segments are considered as required. Note the ? character in this case.
For example:
[Route("v1/location/{deviceOrAppid?}", Name = "AddNewLocation")]

Another info: If you want use a Route Constraint, imagine that you want force that parameter has int datatype, then you need use this syntax:
[Route("v1/location/**{deviceOrAppid:int?}**", Name = "AddNewLocation")]
The ? character is put always before the last } character
For more information see: Optional URI Parameters and Default Values

An additional fact to complement #Kiran Chala's answer -
When we mark any parameter (appid) as optional in the action URI using ? character(for nullable value types) then we must provide default value to the parameter in the method signature as shown below:
[Route("v1/location/{deviceid}/{appid}", Name = "AddNewLocation")]
public location_fromuser Post(string deviceid, int? appid = null)

Ok, I fallen here with my internet research and I continue my way, because the accepted solution not working with dotnet core 3.1.
So here is my solution, following this doc
[HttpPost]
[Route("{name}")]
[Route("{name}/parent/{parentId}")]
public async Task<IActionResult> PostSomething(string name, Guid? parentId = null)
{
return Ok(await Task.FromResult(new List<string>()));
}
By this way many routes go to this single API function

How do I accept an array as an ASP.NET MVC controller action parameter?

I have an ASP.net MVC controller called Designs that has an action with the following signature:
public ActionResult Multiple(int[] ids)
However, when I try to navigate to this action using the url:
http://localhost:54119/Designs/Multiple?ids=24041,24117
The ids parameter is always null. Is there any way to get MVC to convert the ?ids= URL query parameter into an array for the action? I've seen talk of using an action filter but as far as I can tell that will only work for POSTs where the array is passed in the request data rather than in the URL itself.

The default model binder expects this url:
http://localhost:54119/Designs/Multiple?ids=24041&ids=24117
in order to successfully bind to:
public ActionResult Multiple(int[] ids)
{
...
}
And if you want this to work with comma separated values you could write a custom model binder:
public class IntArrayModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
if (value == null || string.IsNullOrEmpty(value.AttemptedValue))
{
return null;
}
return value
.AttemptedValue
.Split(',')
.Select(int.Parse)
.ToArray();
}
}
and then you could apply this model binder to a particular action argument:
public ActionResult Multiple([ModelBinder(typeof(IntArrayModelBinder))] int[] ids)
{
...
}
or apply it globally to all integer array parameters in your Application_Start in Global.asax:
ModelBinders.Binders.Add(typeof(int[]), new IntArrayModelBinder());
and now your controller action might look like this:
public ActionResult Multiple(int[] ids)
{
...
}

To extend on Darin Dimitrov's answer, something you can get away with is accepting a simple string in your URL parameter and converting it to an array yourself:
public ActionResult Multiple(string ids){
int[] idsArray = ids.Split(',').Select(int.Parse).ToArray();
/* ...process results... */
}
If you get a parse error while doing this (because someone passed you a malformed array), you can cause your exception handler to return a 400 Bad Request error instead of the default, more unfriendly 404 Not Found error that MVC returns when an endpoint is not found.

You can also use this URL format, and ASP.NET MVC will do everything for you. But, remember to apply URL encoding.
?param1[0]=3344&param1[1]=2222

I don't know where Groky's URL string was coming from, but I had the same problem with some javascript calling my controller/action. It would build up a URL of null, 1, or many "IDs" from a multiple-select list (which is unique to the solution I'm going to share).
I copy/pasted Darin's custom model binder and decorated my action/parameter, but it didn't work. I still got null valued int[] ids. Even in the "safe" case where I actually did have many IDs.
I ended up changing the javascript to produce an ASP.NET MVC friendly parameter array like
?ids=1&ids=2
I had to do some silly stuff, though
ids || [] #=> if null, get an empty array
[ids || []] #=> if a single item, wrap it in an array
[].concat.apply([], ...) #=> in case I wrapped an array, flatten it
So, the full block was
ids = [].concat.apply([], [ids || []])
id_parameter = 'ids=' + ids.join('&ids=')
It's messy, but it's the first time I had to hack like this in javascript.

.Net Core Answer
For those coming here in recent times, you can do this in .Net Core with:
http://localhost:54119/Designs/Multiple?ids=24041&ids=24117
and:
public ActionResult Multiple([FromQuery] int[] ids)
{
...
}