How to set a subset of properties of an object using data obtained from web (in form of JSON) using DataContractJsonSerializer

Question

I am making a Travel app project consisting of a backend coded in PHP and a UWP app (frontend) coded in C#.

Following represent the "Holiday Package" class implemented in C#

 public class Packages
{
    public string PackageID { get; set; }
    public string Name { get; set; }
    public string Destination { get; set; }
    public string Description { get; set; }
    public int Duration { get; set; }
    public float BasePrice { get; set; }
    public List<string> Images { get; set; }

    public HotelInPackage Hotel { get; set; }

    public string TransportType { get; set; }

    public Packages(string packageID,string name,string destination,string description,int duration,float basePrice,List<string> images)
    {
        PackageID = packageID;
        Name = name;
        Destination = destination;
        Description = description;
        Duration = duration;
        BasePrice = basePrice;
        Images = images;
    }

    public void HotelConstruct(string hotelID,string name,int cat)
    {
        Hotel = new HotelInPackage(hotelID, name, cat);
    }

    public void SetTransport(string transportType)
    {
        TransportType = transportType;
    }

    public void ChangeImageName()
    {
        int i = 0;
        while(i<Images.Count)
        {
            Images[i] = string.Format("Assets/CitiesPlaceholder/{0}.jpg",Images[i]);
            i++;
        }
    }
}

Following is the JSON string returned by the backend

{
"PackageID":"P280",
"Name":"Sigapore Dreams",
"Destination":"Singapore",
"Description":"lorem ipsum,dolor sit amet",
"Duration":5,
"BasePrice":999.2
}

I want to deserialize the above JSON string into the "Packages" class thereby setting its "PackageID", "Name", "Destination", "Description", "Duration" and "BasePrice" properties ie I want to set only a subset of properties using web data

How to implement the above solution using the DataContractJsonSerializer class?

Do I need to Add/Modify any Constructor?

Answer 1

DataContractJsonSerializer will never call a parameterized constructor. Thus, as it stands, since your Packages type lacks a parameterless constructor, it throws an exception because it does not know how to construct an instance of such a type.

You have two ways to enble DataContractJsonSerializer to construct your object. Firstly, you can add a parameterless constructor. It could even be private:

public class Packages
{
    public string PackageID { get; set; }
    public string Name { get; set; }
    public string Destination { get; set; }
    public string Description { get; set; }
    public int Duration { get; set; }
    public float BasePrice { get; set; }
    public List<string> Images { get; set; }

    public HotelInPackage Hotel { get; set; }

    public string TransportType { get; set; }

    Packages()
    {
        Debug.WriteLine("Calling private constructor of " + GetType().FullName);
    }

    public Packages(string packageID, string name, string destination, string description, int duration, float basePrice, List<string> images)
    {
        PackageID = packageID;
        Name = name;
        Destination = destination;
        Description = description;
        Duration = duration;
        BasePrice = basePrice;
        Images = images;
    }
}

Alternatively, if you don't want even a private parameterless constructor, you can mark your type with [DataContract] and [DataMember] attributes:

[DataContract]
public class Packages
{
    [DataMember]
    public string PackageID { get; set; }
    [DataMember]
    public string Name { get; set; }
    [DataMember]
    public string Destination { get; set; }
    [DataMember]
    public string Description { get; set; }
    [DataMember]
    public int Duration { get; set; }
    [DataMember]
    public float BasePrice { get; set; }
    [DataMember]
    public List<string> Images { get; set; }

    [DataMember]
    public HotelInPackage Hotel { get; set; }

    [DataMember]
    public string TransportType { get; set; }

    public Packages(string packageID, string name, string destination, string description, int duration, float basePrice, List<string> images)
    {
        PackageID = packageID;
        Name = name;
        Destination = destination;
        Description = description;
        Duration = duration;
        BasePrice = basePrice;
        Images = images;
    }
}

This works because, for data contract types, the data contract serializer does not call any constructor at all .

Having implemented either of these options for Packages (and, probably, HotelInPackage , which is not included in the question), you can now deserialize your JSON. Only those properties actually present in the JSON will be set.