How to pass model values in a parameter - asp.net

Question

I want to pass values using model as parameter.
This is basically the mvc web api app
This is my Model class
public class ConversionModel
{
public double value { get; set; }
public int qty { get; set; }
public double result { get; set; }
public string from { get; set; }
public string to { get; set; }
}
This is My controller code
[HttpGet]
[Route("api/Conversion/Currency")]
public double Currency(ConversionModel c)
{
return c.value;
}
And my url is
http://localhost:5267/api/Conversion/Currency?value=123
But is showing me an error
Object reference not set to an instance of an object.

Answer 1

You cannot pass an object in query string. You need to write all parameters in your Route annotation.
[Route("api/Conversion/Currency/{value}/{qty}/{result}/{from}/{to}")]
And then in your action:
public double Currency(double value, int qty, double result, string from, string to) {
var conversionModel = new ConversionModel();
conversionModel.value = value;
conversionModel.qty = qty;
conversionModel.result = result;
conversionModel.from = from;
conversionModel.to = to;
// Rest of your code.
}

Answer 2

You are only providing an integer value, it cannot be converted to ConversionModel.
You can either use post
[HttpPost]
public double Currency([FromBody]ConversionModel c)
which is more suitable for a complex object.
Or pass the values as separate get parameters, constructing a ConversionModel in the method body.
Or use get with [FromUri]; this still requires supplying all the individual parameter-values. (see here)
Passing a collection of individual values is a little fragile/clumsy, I would prefer to use post. Besides which, it is unlikely that you need all the values, and an instance of the class, if you will be simply returning a double value, so post is most likely to be appropriate.