WCF service proxy not setting "FieldSpecified" property

Question

I've got a WCF DataContract that looks like the following:

namespace MyCompanyName.Services.Wcf
{
  [DataContract(Namespace = "http://mycompanyname/services/wcf")]
  [Serializable]
  public class DataContractBase
  {
    [DataMember]
    public DateTime EditDate { get; set; }

    // code omitted for brevity...
  }
}

When I add a reference to this service in Visual Studio, this proxy code is generated:

/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("System.Xml", "2.0.50727.3082")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(Namespace="http://mycompanyname/services/wcf")]
public partial class DataContractBase : object, System.ComponentModel.INotifyPropertyChanged {

    private System.DateTime editDateField;

    private bool editDateFieldSpecified;

    /// <remarks/>
    [System.Xml.Serialization.XmlElementAttribute(Order=0)]
    public System.DateTime EditDate {
        get {
            return this.editDateField;
        }
        set {
            this.editDateField = value;
            this.RaisePropertyChanged("EditDate");
        }
    }

    /// <remarks/>
    [System.Xml.Serialization.XmlIgnoreAttribute()]
    public bool EditDateSpecified {
        get {
            return this.editDateFieldSpecified;
        }
        set {
            this.editDateFieldSpecified = value;
            this.RaisePropertyChanged("EditDateSpecified");
        }
    }

    // code omitted for brevity...
}

As you can see, besides generating a backing property for EditDate, an additional <propertyname>Specified property is generated. All good, except that when I do the following:

DataContractBase myDataContract = new DataContractBase();
myDataContract.EditDate = DateTime.Now;

new MyServiceClient.Update(new UpdateRequest(myDataContract));

the EditDate was not getting picked up by the endpoint of the service (does not appear in the transmitted XML).

I debugged the code and found that, although I was setting EditDate, the EditDateSpecified property wasn't being set to true as I would expect; hence, the XML serializer was ignoring the value of EditDate, even though it's set to a valid value.

As a quick hack I modified the EditDate property to look like the following:

   /// <remarks/>
    [System.Xml.Serialization.XmlElementAttribute(Order=0)]
    public System.DateTime EditDate {
        get {
            return this.editDateField;
        }
        set {
            this.editDateField = value;

            // hackhackhack
            if (value != default(System.DateTime))
            {
              this.EditDateSpecified = true;
            }
            // end hackhackhack

            this.RaisePropertyChanged("EditDate");
        }
    }

Now the code works as expected, but of course every time I re-generate the proxy, my modifications are lost. I could change the calling code to the following:

DataContractBase myDataContract = new DataContractBase();
myDataContract.EditDate = DateTime.Now;
myDataContract.EditDateSpecified = true;

new MyServiceClient.Update(new UpdateRequest(myDataContract));

but that also seems like a hack-ish waste of time.

So finally, my question: does anyone have a suggestion on how to get past this unintuitive (and IMO broken) behavior of the Visual Studio service proxy generator, or am I simply missing something?

Answer 1

It might be a bit unintuitive (and caught me off guard and reeling, too!) - but it's the only proper way to handle elements that might or might not be specified in your XML schema.

And it also might seem counter-intuitive that you have to set the xyzSpecified flag yourself - but ultimately, this gives you more control, and WCF is all about the Four Tenets of SOA of being very explicit and clear about your intentions.

So basically - that's the way it is, get used to it :-) There's no way "past" this behavior - it's the way the WCF system was designed, and for good reason, too.

What you always can do is catch and handle the this.RaisePropertyChanged("EditDate"); event and set the EditDateSpecified flag in an event handler for that event.

Answer 2

try this

[DataMember(IsRequired=true)]
public DateTime EditDate { get; set; }

This should omit the EditDateSpecified property since the field is specified as required

Answer 3

Rather than change the setters of the autogenerated code, you can use an extension class to 'autospecify' (bind the change handler event). This could have two implementations -- a "lazy" one (Autospecify) using reflection to look for fieldSpecified based on the property name, rather than listing them all out for each class in some sort of switch statement like Autonotify:

Lazy

public static class PropertySpecifiedExtensions
{
    private const string SPECIFIED_SUFFIX = "Specified";

    /// <summary>
    /// Bind the <see cref="INotifyPropertyChanged.PropertyChanged"/> handler to automatically set any xxxSpecified fields when a property is changed.  "Lazy" via reflection.
    /// </summary>
    /// <param name="entity">the entity to bind the autospecify event to</param>
    /// <param name="specifiedSuffix">optionally specify a suffix for the Specified property to set as true on changes</param>
    /// <param name="specifiedPrefix">optionally specify a prefix for the Specified property to set as true on changes</param>
    public static void Autospecify(this INotifyPropertyChanged entity, string specifiedSuffix = SPECIFIED_SUFFIX, string specifiedPrefix = null)
    {
        entity.PropertyChanged += (me, e) =>
        {
            foreach (var pi in me.GetType().GetProperties().Where(o => o.Name == specifiedPrefix + e.PropertyName + specifiedSuffix))
            {
                pi.SetValue(me, true, BindingFlags.SetField | BindingFlags.SetProperty, null, null, null);
            }
        };
    }

    /// <summary>
    /// Create a new entity and <see cref="Autospecify"/> its properties when changed
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="specifiedSuffix"></param>
    /// <param name="specifiedPrefix"></param>
    /// <returns></returns>
    public static T Create<T>(string specifiedSuffix = SPECIFIED_SUFFIX, string specifiedPrefix = null) where T : INotifyPropertyChanged, new()
    {
        var ret = new T();
        ret.Autospecify(specifiedSuffix, specifiedPrefix);
        return ret;
    }
}

This simplifies writing convenience factory methods like:

public partial class MyRandomClass 
{
    /// <summary>
    /// Create a new empty instance and <see cref="PropertySpecifiedExtensions.Autospecify"/> its properties when changed
    /// </summary>
    /// <returns></returns>
    public static MyRandomClass Create()
    {
        return PropertySpecifiedExtensions.Create<MyRandomClass>();
    }
}

A downside (other than reflection, meh) is that you have to use the factory method to instantiate your classes or use .Autospecify before (?) you make any changes to properties with specifiers.

No Reflection

If you don't like reflection, you could define another extension class + interface:

public static class PropertySpecifiedExtensions2
{
    /// <summary>
    /// Bind the <see cref="INotifyPropertyChanged.PropertyChanged"/> handler to automatically call each class's <see cref="IAutoNotifyPropertyChanged.Autonotify"/> method on the property name.
    /// </summary>
    /// <param name="entity">the entity to bind the autospecify event to</param>
    public static void Autonotify(this IAutoNotifyPropertyChanged entity)
    {
        entity.PropertyChanged += (me, e) => ((IAutoNotifyPropertyChanged)me).WhenPropertyChanges(e.PropertyName);
    }

    /// <summary>
    /// Create a new entity and <see cref="Autonotify"/> it's properties when changed
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <returns></returns>
    public static T Create<T>() where T : IAutoNotifyPropertyChanged, new()
    {
        var ret = new T();
        ret.Autonotify();
        return ret;
    }
}

/// <summary>
/// Used by <see cref="PropertySpecifiedExtensions.Autonotify"/> to standardize implementation behavior
/// </summary>
public interface IAutoNotifyPropertyChanged : INotifyPropertyChanged
{
    void WhenPropertyChanges(string propertyName);
}

And then each class themselves defines the behavior:

public partial class MyRandomClass: IAutoNotifyPropertyChanged
{
    public void WhenPropertyChanges(string propertyName)
    {
        switch (propertyName)
        {
            case "field1": this.field1Specified = true; return;
            // etc
        }
    }
}

The downside to this is, of course, magic strings for property names making refactoring difficult, which you could get around with Expression parsing?