C# WebApi getting The parameters dictionary contains a null entry error

Question

Have the following api method:

[HttpPut]
[Route("Customers/{CustomerId}/Search", Name = "CustomerSearch")]
[ResponseType(typeof(SearchResults))]
public async Task<IHttpActionResult> Search([FromBody]SearchFilters filters, long? CustomerId = null)
{
    //This func searches for some subentity inside customers
}

when I try http://localhost/Customers/Search/keyword, the following works but when I try http://localhost/Customers/Search, I am getting following error:

messageDetail=The parameters dictionary contains a null entry for parameter 'CustomerId' of non-nullable type 'System.Int64' for method 'System.Threading.Tasks.Task1[System.Web.Http.IHttpActionResult] GetById(Int64, System.Nullable1[System.Int64])' in '....'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.

[HttpGet]
[Route("Customers/Search/{keyword}", Name = "GetCustomersByKeyword")]
public async Task<IHttpActionResult> SearchCustomers(string keyword = "")
{
    //This func searches for customers based on the keyword in the customer name
}

Can anyone help how to fix the issue? Or correct me what am i doing wrong?

Answer 1

Optional parameter should be used as the end of the template as they can be excluded from the url.

Also by using a route constraint for the customer id you will make sure that a key word is not mistaken for a customer id.

Reference: Attribute Routing in ASP.NET Web API 2

//PUT Customers/10/Search
[HttpPut]
[Route("Customers/{CustomerId:long}/Search", Name = "CustomerSearch")]
[ResponseType(typeof(SearchResults))]
public async Task<IHttpActionResult> Search(long CustomerId, [FromBody]SearchFilters filters, ) {
    //This func searches for some subentity inside customers
}

//GET Customers/Search    
//GET Customers/Search/keyword
[HttpGet]
[Route("Customers/Search/{keyword?}", Name = "GetCustomersByKeyword")]
public async Task<IHttpActionResult> SearchCustomers(string keyword = "") {
    //This func searches for customers based on the keyword in the customer name
}