用于自定义值类型的DataContractSerializer

Question

I have a WCF service which exposes a type TestTypeOne which currently has a string property called ProductId :

public class TestTypeOne
{
    [DataMember(Name = "ProductId")]
    public string ProductId { get; set; } //note it's a string at the moment
}

I want to change the type of this property from string to a custom value type called ProductId , but without breaking the WCF contract (this is only for the server side, the clients should see the ProductId as a string still.)

public class TestTypeOne
{
    [DataMember(Name = "ProductId")]
    public ProductId ProductId { get; set; }
}

The custom type is something like this (most code removed for brevity):

public struct ProductId : IEquatable<ProductId>
{
    readonly string productId;

    public ProductId(string productId)
    {
        this.productId = productId
    }

    public override string ToString() => productId ?? string.Empty;
}

Using the following test code:

var sb = new StringBuilder();
using (var writer = new XmlTextWriter(new StringWriter(sb)))
{
    var dto = new TestTypeOne {
        ProductId = new ProductId("1234567890123")
    };

    var serializer = new DataContractSerializer(typeof(TestTypeOne));
    serializer.WriteObject(writer, dto);
    writer.Flush();
}

Console.WriteLine(sb.ToString());

The expected output when serializing should be:

<Scratch.TestTypeOne xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Tests">
    <ProductId>1234567890123</ProductId>
</Scratch.TestTypeOne>

I have tried implementing ISerializable but that seems to only let me control the content of the ProductId xml tag, not the tag itself (so I can make things like <ProductId><something>1234113</something></ProductId> happen).

Ideally I am after something I can do to the ProductId type itself, as this type is used in many places, and many contracts.

Answer 1

I think easiest way would be to implement IXmlSerializable :

public struct ProductId : IXmlSerializable
{
    readonly string productId;

    public ProductId(string productId)
    {
        this.productId = productId;
    }

    public override string ToString() => productId ?? string.Empty;

    XmlSchema IXmlSerializable.GetSchema() {
        return null;
    }

    void IXmlSerializable.ReadXml(XmlReader reader) {
        this = new ProductId(reader.ReadString());
    }

    void IXmlSerializable.WriteXml(XmlWriter writer) {
        writer.WriteString(this.productId);
    }
}

To adjust WCF xsd generation for this case (force it to generate xs:string ) - you can use data contract surrogate for xsd generation. For example you can have such suggorate:

public class ProductIdSurrogate : IDataContractSurrogate {
    public Type GetDataContractType(Type type) {
        if (type == typeof(ProductId))
            return typeof(string);
        return type;
    }

    public object GetObjectToSerialize(object obj, Type targetType) {
        throw new NotImplementedException();
    }

    public object GetDeserializedObject(object obj, Type targetType) {
        throw new NotImplementedException();
    }

    public object GetCustomDataToExport(MemberInfo memberInfo, Type dataContractType) {
        return null;
    }

    public object GetCustomDataToExport(Type clrType, Type dataContractType) {
        return null;
    }

    public void GetKnownCustomDataTypes(Collection<Type> customDataTypes) {
        throw new NotImplementedException();
    }

    public Type GetReferencedTypeOnImport(string typeName, string typeNamespace, object customData) {
        throw new NotImplementedException();
    }

    public CodeTypeDeclaration ProcessImportedType(CodeTypeDeclaration typeDeclaration, CodeCompileUnit compileUnit) {
        throw new NotImplementedException();
    }
}

Whose only purpose is say that data contract for ProductId type is really string .

Then you can use this surrogate for schema generation:

var exporter = new XsdDataContractExporter();
exporter.Options = new ExportOptions();
exporter.Options.DataContractSurrogate = new ProductIdSurrogate();
exporter.Export(typeof(TestTypeOne));

You can use this approach for serialization itself, but I find it more complicated.

You can read more info about surrogates and WCF here , and the very bottom there is an example of how you can use surrogate for WSDL generation endpoint (section "To Use a surrogate for Metadata Export").

Answer 2

Have you tried adding the DataContract/DataMember attributes to this ProductId class as well?

ie:

[DataContract]
public struct ProductId : IEquatable<ProductId>
{

[DataMember]
readonly string productId;

public ProductId(string productId)
{
    this.productId = productId
}

public override string ToString() => productId ?? string.Empty;

}

Also, the name property (Name="ProductId") in this case is not needed, as the variable name is the same as the one you're overriding it with.