ASP.NET Web Api - Unable to cast object of type 'Fidly.Dtos.CustomerDto' to type 'Fidly.Models.Customer'.

Question

User-1128363788 posted

I have a web api request shown below using Postman:

and this is my Custom Validation class which has a line converts 'validationContext' which is supposed to be of type 'customerDto'. The implicit casting to 'Customer' fails and throws an exception. I tried also explicit casting but it doesn't work with 'validationContext'.

How to do casting?

Answer 1

User753101303 posted

Hi,

mahmoud_arafa

supposed to be of type 'customerDto'. The implicit casting to 'Customer' fails

More likely you want to cast CustomerDto ?

Edit: if you really declared your class for implicit casting (that is https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/implicit what you shown is explicit casting), I doubt casting from object to Customer could go through an implicit casting though I never tried.

Answer 2

User1120430333 posted

A class is a blueprint for an object instance, which has public  properties, private variables and behaviors/methods that are unique for the object. You cannot cast a object that is defined by one class to be an object that is defined by another class, the cast. 

https://alfredjava.wordpress.com/2008/07/08/class-vs-object-vs-instance/

Two casting rules are the following:

1) The cast of the object must be of the same type, which is two objects defined by the same class.

2) .NET will not allow the casting of an object across namespaces even if it's the same object, like trying to cast namespacex.objectxyz to namespacez.objectxyz, 

Customerdto should be just a simple object with public properties only with no behavior. Customer I am going to assume is a domain object that has public properties that may have behavior. You are going to have to map the public properties of the DTO to the public properties of the domain object by doing the mapping manually or using a library like Automapper.

https://www.infoworld.com/article/3192900/how-to-work-with-automapper-in-c.html

example...

 public ProjectViewModels.Project GetProjectById(int id)
        {
            var responseDto = _webApi.GetProjByIdApi(id);

            var project = new ProjectViewModels.Project
            {
                ProjectId = responseDto.ProjectId,
                ClientName = responseDto.ClientName,
                ProjectName = responseDto.ProjectName,
                Technology = responseDto.Technology,
                ProjectType = responseDto.ProjectType,
                StartDate = responseDto.StartDate,
                EndDate = responseDto.EndDate,
                Cost = responseDto.Cost
            };

            return project;
        }

 

Answer 3

User1520731567 posted

Hi mahmoud_arafa,

var customer=(Customer)validationContext.ObjectInstance;

Do your error happened on this line?

I suggest you could use the same model,if your want different,you could create a ViewModel,

for example: create a viewmodel named Customer2 

var customer=(Customer)validationContext.ObjectInstance; 

Customer2 newcustomer = new Customer2();
newcustomer.Id = customer.Id;
newcustomer.xx= customer.xx; 
...

if  your fields is too much,I suggest you could use autoMapper to convert,

for example:

install autoMapper in Nuget,and then:

var customer=(Customer)validationContext.ObjectInstance; 

Mapper.Initialize(cfg => cfg.CreateMap<Customer, Customer2>());
Customer2 newcustomer= Mapper.Map<Customer2>(model);

Best Regards.

Yuki Tao