[wcf] When to use DataContract and DataMember attributes?

I am very confused about the DataContract attribute in WCF. As per my knowledge it is used for serializating user defined type like classes. I wrote one class which is exposed at client side like this.

[DataContract]
public class Contact
{
    [DataMember]
    public int Roll { get; set; }

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

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

    [DataMember]
    public int Age { get; set; }
}

It is working properly but when I remove DataContract and DataMember it also works properly. I can't understand why it is working properly. Can any one tell me what is the actual use of DataContract?

My service contract looks like this

[ServiceContract]    
public interface IRestServiceImpl
{
    [OperationContract]        
    Contact XmlData(string id);      
}

A data contract is a formal agreement between a service and a client that abstractly describes the data to be exchanged.

Data contract can be explicit or implicit. Simple type such as int, string etc has an implicit data contract. User defined object are explicit or Complex type, for which you have to define a Data contract using [DataContract] and [DataMember] attribute.

A data contract can be defined as follows:

• It describes the external format of data passed to and from service operations

• It defines the structure and types of data exchanged in service messages

• It maps a CLR type to an XML Schema
• It defines how data types are serialized and deserialized. Through serialization, you convert an object into a sequence of bytes that can be transmitted over a network. Through deserialization, you reassemble an object from a sequence of bytes that you receive from a calling application.
• It is a versioning system that allows you to manage changes to structured data

We need to include System.Runtime.Serialization reference to the project. This assembly holds the DataContract and DataMember attribute.

In terms of WCF, we can communicate with the server and client through messages. For transferring messages, and from a security prospective, we need to make a data/message in a serialized format.

For serializing data we use [datacontract] and [datamember] attributes. In your case if you are using datacontract WCF uses DataContractSerializer else WCF uses XmlSerializer which is the default serialization technique.

Let me explain in detail:

basically WCF supports 3 types of serialization:

1. XmlSerializer
2. DataContractSerializer
3. NetDataContractSerializer

XmlSerializer :- Default order is Same as class

DataContractSerializer/NetDataContractSerializer :- Default order is Alphabetical

XmlSerializer :- XML Schema is Extensive

DataContractSerializer/NetDataContractSerializer :- XML Schema is Constrained

XmlSerializer :- Versioning support not possible

DataContractSerializer/NetDataContractSerializer :- Versioning support is possible

XmlSerializer :- Compatibility with ASMX

DataContractSerializer/NetDataContractSerializer :- Compatibility with .NET Remoting

XmlSerializer :- Attribute not required in XmlSerializer

DataContractSerializer/NetDataContractSerializer :- Attribute required in this serializing

so what you use depends on your requirements...

Since a lot of programmers were overwhelmed with the [DataContract] and [DataMember] attributes, with .NET 3.5 SP1, Microsoft made the data contract serializer handle all classes - even without any of those attributes - much like the old XML serializer.

So as of .NET 3.5 SP1, you don't have to add data contract or data member attributes anymore - if you don't then the data contract serializer will serialize all public properties on your class, just like the XML serializer would.

HOWEVER: by not adding those attributes, you lose a lot of useful capabilities:

• without [DataContract], you cannot define an XML namespace for your data to live in
• without [DataMember], you cannot serialize non-public properties or fields
• without [DataMember], you cannot define an order of serialization (Order=) and the DCS will serialize all properties alphabetically
• without [DataMember], you cannot define a different name for your property (Name=)
• without [DataMember], you cannot define things like IsRequired= or other useful attributes
• without [DataMember], you cannot leave out certain public properties - all public properties will be serialized by the DCS

So for a "quick'n'dirty" solution, leaving away the [DataContract] and [DataMember] attributes will work - but it's still a good idea to have them on your data classes - just to be more explicit about what you're doing, and to give yourself access to all those additional features that you don't get without them...

DataMember attribute is not mandatory to add to serialize data. When DataMember attribute is not added, old XMLSerializer serializes the data. Adding a DataMember provides useful properties like order, name, isrequired which cannot be used otherwise.

A data contract is a formal agreement between a service and a client that abstractly describes the data to be exchanged. That is, to communicate, the client and the service do not have to share the same types, only the same data contracts. A data contract precisely defines, for each parameter or return type, what data is serialized (turned into XML) to be exchanged.

Windows Communication Foundation (WCF) uses a serialization engine called the Data Contract Serializer by default to serialize and deserialize data (convert it to and from XML). All .NET Framework primitive types, such as integers and strings, as well as certain types treated as primitives, such as DateTime and XmlElement, can be serialized with no other preparation and are considered as having default data contracts. Many .NET Framework types also have existing data contracts.

You can find the full article here.

Also when you call from http request it will work properly but when your try to call from net.tcp that time you get all this kind stuff

1. Data contract: It specifies that your entity class is ready for Serialization process.

2. Data members: It specifies that the particular field is part of the data contract and it can be serialized.