Default values in list query parameter - asp.net-core

Question

I am trying to display default values in Swashbuckle. Is there a way to define default values in a query list parameter in a .NET Core API.
Something like:
[HttpGet("test")]
public ActionResult<string> TestFunc([FromQuery, BindRequired] List<string> testList = ["value1", "value2"]) {
//Do some stuff
return Ok(results);
}

Answer 1

As far as I know, we couldn't set the default parameter value must be compile-time constant which means we couldn't set a default value for a list or array of string.
That means there is no way to set the defualt value inside the web api paramter.
If you want to show the default value inside the swagger. You could create a class which inherit from IOperationFilter.
Then you could check the paramter name, if the name is equals the testList ,you could set the custom description.
More details, you could refer to below codes example:
Custom class:
public class ParameterClass : IOperationFilter
{
public void Apply(OpenApiOperation operation, OperationFilterContext context)
{
if (operation.Parameters == null)
{
return;
}
foreach (var parameter in operation.Parameters) {
if (parameter.Name == "testList")
{
parameter.Description = #"Default value: ['value1', 'value2']";
}
}
}
}
Register the swaggergen with filter :
services.AddSwaggerGen(c =>
{
c.OperationFilter<ParameterClass>();
});
Result:
Update:
If you want to set the parameter like query string, you could modify the apply method as below:
public void Apply(OpenApiOperation operation, OperationFilterContext context)
{
if (operation.Parameters == null)
{
return;
}
foreach (var parameter in operation.Parameters) {
if (parameter.Name == "testList")
{
parameter.In = 0;
parameter.Description = #"['value1', 'value2']";
parameter.Schema = new OpenApiSchema() { Type = "string" ,Items = null };
}
}
}
Result: