how to not return null when a Data member field is not set in the data contract

问题

I'm having a strange problem with my WCF service that returns data in JSON format. I want to return information about a "Customer" based on the request sent by client.

Client can request what fields of information about a customer they need and the service needs to send only that information about the customer.

For Example: If client asks for a list of customers and says they want firstname, lastname, city of each customer then server should send a json response with each field name and corresponding value

Something like...

[
  {"firstname":"john","lastname":"Goodman","city" :"NY"},
  {"firstname":"brad","lastname":"newman","city" :"LA"}
]

if client asks for list of customers with ID and city fields only then the response should look like this

[
  {"id" :"1234","city" :"NY"},
  {"id":"1235","city" :"LA"}
]

My initial design was to implement a "Customer" class and then have each possible "field" as a field of this class. Then inside my service method, I was getting the list of fields specified by the client and instantiating customer objects with only those properties set.

My operation contract looks like this

[OperationContract]
[WebGet(BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Json, UriTemplate = "Customers?fields={value}")]
List<Customer> GetCustomers(string value);

But the problem is when I decorate the class with "DataContract" and each Field as "DataMember"....if some properties are not set, they still get deserialized as NULL when sent to client. I dont want this to happen.

Also, the list of possible fields a customer is very long and so the class became very large. I would rather store these fields as an enum collection in my service rather than fields of a class.

I then thought of having my Operation return a IDictionary<string,object> and then add each field and value iteratively to this collection. That didn't work because, when a dictionary is serialized it shows {"Key:dfas", "Value:34"} etc etc. not what i want

So I'm kinda stuck. What's the best way to solve this problem?

Can I mark my [DataContract] such a way that if [DataMember] properties are not set i.e, null then they shouldn't be serialized and send to client at all?

回答1:

You can mark each data member so it won't be serialized if it's null. The essential part is: EmitDefaultValue = false

[DataContract]
public class Person
{
    [DataMember(EmitDefaultValue = false)]
    public string id { get; set; }

    [DataMember(EmitDefaultValue = false)]
    public string firstname { get; set; }

    [DataMember(EmitDefaultValue = false)]
    public string lastname { get; set; }

    [DataMember(EmitDefaultValue = false)]
    public string city { get; set; }
}

来源：https://stackoverflow.com/questions/5685045/how-to-not-return-null-when-a-data-member-field-is-not-set-in-the-data-contract

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wcf

json

serialization

datacontractserializer