Question

I am new to WCF. I was able to successfully create a client for the GeoNames service, but now that I am trying to do the same for Yahoo GeoPlanet, I can’t seem to get the XML to deserialize into my DataContract types. What is the right way to do this? Here is what I am working with:

Sample REST response:

<places xmlns="http://where.yahooapis.com/v1/schema.rng" 
    xmlns:yahoo="http://www.yahooapis.com/v1/base.rng" 
    yahoo:start="0" yahoo:count="247" yahoo:total="247">
    <place yahoo:uri="http://where.yahooapis.com/v1/place/23424966" 
        xml:lang="en-US">
        <woeid>23424966</woeid>
        <placeTypeName code="12">Country</placeTypeName>
        <name>Sao Tome and Principe</name>
    </place>
    <place yahoo:uri="http://where.yahooapis.com/v1/place/23424824" 
        xml:lang="en-US">
        <woeid>23424824</woeid>
        <placeTypeName code="12">Country</placeTypeName>
        <name>Ghana</name>
    </place>
    ...
</places>

Contract Interface & Client:

[ServiceContract]
public interface IConsumeGeoPlanet
{
    [OperationContract]
    [WebGet(
        UriTemplate = "countries?appid={appId}",
        ResponseFormat = WebMessageFormat.Xml,
        BodyStyle = WebMessageBodyStyle.Bare
    )]
    GeoPlanetResults<GeoPlanetPlace> Countries(string appId);
}

public sealed class GeoPlanetConsumer : ClientBase<IConsumeGeoPlanet>
{
    public GeoPlanetResults<GeoPlanetPlace> Countries(string appId)
    {
        return Channel.Countries(appId);
    }
}

Deserialization Types:

[DataContract(Name = "places", 
    Namespace = "http://where.yahooapis.com/v1/schema.rng")]
public sealed class GeoPlanetResults<T> : IEnumerable<T>
{
    public List<T> Items { get; set; }

    public IEnumerator<T> GetEnumerator()
    {
        return Items.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}


[DataContract]
public class GeoPlanetPlace
{
    [DataMember(Name = "woeid")]
    public int WoeId { get; set; }

    [DataMember(Name = "placeTypeName")]
    public string Type { get; set; }

    [DataMember(Name = "name")]
    public string Name { get; set; }

}

I know this is wrong. In my geonames client, my GeoNamesResults class has a [DataContract] attribute with no properties, and a [DataMember(Name = "geonames")] attribute on the Items property. This doesn’t work for GeoPlanet though, I kept getting deserialization exceptions. The only way I could get the Countries(appId) method to execute without exceptions was by putting the Name and Namespace in the DataContract attribute. However when I do this, I have no idea how to get the results deserialized into the Items collection (it is null).

What should I do?

Answer 1

The DataContractSerializer doesn’t support the full XML specification, only a subset of it. On thing it doesn’t support is attributes, which are used extensively in the sample response you showed. In this case, you’ll need to use the XmlSerializer, and define the types accordingly (using the attributes in System.Xml.Serialization, instead of the ones on System.Runtime.Serialization). The code below shows how to retrieve the sample XML you posted.

public class StackOverflow_8022154
{
    const string XML = @"<places xmlns=""http://where.yahooapis.com/v1/schema.rng""  
    xmlns:yahoo=""http://www.yahooapis.com/v1/base.rng""  
    yahoo:start=""0"" yahoo:count=""247"" yahoo:total=""247""> 
    <place yahoo:uri=""http://where.yahooapis.com/v1/place/23424966""  
        xml:lang=""en-US""> 
        <woeid>23424966</woeid> 
        <placeTypeName code=""12"">Country</placeTypeName> 
        <name>Sao Tome and Principe</name> 
    </place> 
    <place yahoo:uri=""http://where.yahooapis.com/v1/place/23424824""  
        xml:lang=""en-US""> 
        <woeid>23424824</woeid> 
        <placeTypeName code=""12"">Country</placeTypeName> 
        <name>Ghana</name> 
    </place> 
</places>";

    const string ElementsNamespace = "http://where.yahooapis.com/v1/schema.rng";
    const string YahooNamespace = "http://www.yahooapis.com/v1/base.rng";
    const string XmlNamespace = "http://www.w3.org/XML/1998/namespace";

    [XmlType(Namespace = ElementsNamespace, TypeName = "places")]
    [XmlRoot(ElementName = "places", Namespace = ElementsNamespace)]
    public class Places
    {
        [XmlAttribute(AttributeName = "start", Namespace = YahooNamespace)]
        public int Start { get; set; }
        [XmlAttribute(AttributeName = "count", Namespace = YahooNamespace)]
        public int Count;
        [XmlAttribute(AttributeName = "total", Namespace = YahooNamespace)]
        public int Total;
        [XmlElement(ElementName = "place", Namespace = ElementsNamespace)]
        public List<Place> AllPlaces { get; set; }

        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("Places[start={0},count={1},total={2}]:", this.Start, this.Count, this.Total);
            sb.AppendLine();
            foreach (var place in this.AllPlaces)
            {
                sb.AppendLine("   " + place.ToString());
            }

            return sb.ToString();
        }
    }
    [XmlType(TypeName = "place", Namespace = ElementsNamespace)]
    public class Place
    {
        [XmlAttribute(AttributeName = "uri", Namespace = YahooNamespace)]
        public string Uri { get; set; }
        [XmlAttribute(AttributeName = "lang", Namespace = XmlNamespace)]
        public string Lang { get; set; }
        [XmlElement(ElementName = "woeid")]
        public string Woeid { get; set; }
        [XmlElement(ElementName = "placeTypeName")]
        public PlaceTypeName PlaceTypeName;
        [XmlElement(ElementName = "name")]
        public string Name { get; set; }

        public override string ToString()
        {
            return string.Format("Place[Uri={0},Lang={1},Woeid={2},PlaceTypeName={3},Name={4}]",
                this.Uri, this.Lang, this.Woeid, this.PlaceTypeName, this.Name);
        }
    }
    [XmlType(TypeName = "placeTypeName", Namespace = ElementsNamespace)]
    public class PlaceTypeName
    {
        [XmlAttribute(AttributeName = "code")]
        public string Code { get; set; }
        [XmlText]
        public string Value { get; set; }

        public override string ToString()
        {
            return string.Format("TypeName[Code={0},Value={1}]", this.Code, this.Value);
        }
    }
    [ServiceContract]
    public interface IConsumeGeoPlanet
    {
        [OperationContract]
        [WebGet(
            UriTemplate = "countries?appid={appId}",
            ResponseFormat = WebMessageFormat.Xml,
            BodyStyle = WebMessageBodyStyle.Bare
        )]
        [XmlSerializerFormat]
        Places Countries(string appId);
    }

    public sealed class GeoPlanetConsumer : ClientBase<IConsumeGeoPlanet>
    {
        public GeoPlanetConsumer(string address)
            : base(new WebHttpBinding(), new EndpointAddress(address))
        {
            this.Endpoint.Behaviors.Add(new WebHttpBehavior());
        }

        public Places Countries(string appId)
        {
            return Channel.Countries(appId);
        }
    }

    [ServiceContract]
    public class SimulatedYahooService
    {
        [WebGet(UriTemplate = "*")]
        public Stream GetData()
        {
            WebOperationContext.Current.OutgoingResponse.ContentType = "text/xml";
            return new MemoryStream(Encoding.UTF8.GetBytes(XML));
        }
    }

    public static void Test()
    {
        Console.WriteLine("First a simpler test with serialization only.");
        XmlSerializer xs = new XmlSerializer(typeof(Places));
        MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(XML));
        object o = xs.Deserialize(ms);
        Console.WriteLine(o);

        Console.WriteLine();
        Console.WriteLine("Now in a real service");
        Console.WriteLine();
        string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
        WebServiceHost host = new WebServiceHost(typeof(SimulatedYahooService), new Uri(baseAddress));
        host.Open();
        Console.WriteLine("Host opened");

        GeoPlanetConsumer consumer = new GeoPlanetConsumer(baseAddress);
        Places places = consumer.Countries("abcdef");
        Console.WriteLine(places);
    }
}