When to use DataContract and DataMember attributes?

Question

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);      
}

Nakitanalani

A perfect answer is here #5682342 – Schwinn

Answer 1

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...

Io

you mean by default all the data types are internally marked as serializable and we used DataContract/DataMember to restrict them. – Necromancy

@Santosh: if you have a class with some public properties, those will be serialized by the WCF Data Contract Serializer, unless you explicitly apply [DataContract]/[DataMember] .- then it's 100% up to you to say what gets serialized and what not – Io

@Io without [DataMember], you cannot serialize non-public properties or fields . In my case without [DataMember], i cannot even serialize public properties. So that you have to use it, this is not an option. I am using .net 4.0 – Phycomycete

@Arthis: that's not entirely true. As of .NET 3.5 SP1, WCF will happily serialize classes without any [DataContract] and [DataMember] attributes... but as soon as you start using one of those attributes, then this "default" behavior will stop working - as soon as you have a single [DataMember] in your class, from that point on, only those properties with this attribute will be serialized. – Io

Youhou! it rocks!! Merci beaucoup! – Phycomycete

Is this still valid? I am getting an exception when trying to add a service reference to a service which uses an object without data contract & data member attributes. The exception suggests me to add that in, which resolves the issue once added. – Jacob

@Ross: yes, it's still valid – Io

Actually, I found that in my particular use case, where I had a WCF rest service, I needed to add [DataMember] to every attribute in order for the parameter binding (and help page) to work. To making a WCF rest service, note that BodyStyle is very important when making requests from Postman/Fiddler! – Wayworn

Answer 2

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...

Hurrah

Though not directly supported by XmlSerializer, you still can implement some form of manual version support with XMLSerializer by using the different events of the serializer, like UnknownElement event, you can go around most schema changes. If your object includes some Version member, you could base the versioning on this. Else, you would have to detect the changes and act accordingly. It is not as robust as the DataContractSerializer version but can come around to be usefult when required. – Coldhearted

Answer 3

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.

Maomaoism

That's all true and fine, but it doesn't really answer the OP's question as to why the data contract serializer also works without any [DataContract] and [DataMember] attributes on your classes.... – Io

Can any one tell me what is the actual use of DataContract? - I think at least part of the question is answered. – Dayton

Answer 4

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.

Minim

Answer 5

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.

Idell

Answer 6

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

Overlive

Answer 7

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.

Multiflorous

Answer 8

The data is to be transferred and processed within service and they store the values, so in the WCF terminology they are called “Data Contract”.

Where each member of the Class; i.e., The data contract is called “Data Member” and they are also to be decorated with the Attributes.

Source

Socage