An existing connection was forcibly closed by the remote host in WCF

Question

I have an abstract class called 'Template' defined as:

[DataContract]
public abstract class Template
{
    [DataMember]
    public virtual int? Id { get; set; }
    [DataMember]
    public virtual string Title { get; set; }
    [DataMember]
    public virtual byte[] TemplateDoc { get; set; }
    [DataMember]
    public virtual bool IsSystemTemplate { get; set; }        
}

Two derived classes: UserTemplate and SystemTemplate implements above abstract class, which are defined as:

public class UserTemplate : Template
{
    [DataMember]
    public virtual Int32? OfficeId { get; set; }

    [DataMember]
    public virtual Int32? UserId { get; set; }

    protected UserTemplate() { }

    public UserTemplate(string title, byte[] templateDoc, string templateDocName, TemplateType templateType, int officeId, int? userId)
    {
        this.Title = title;
        this.TemplateDoc = templateDoc;
        this.IsSystemTemplate = false;
        this.OfficeId = officeId;
        this.UserId = userId;
    }
}

public class SystemTemplate : Template
{
    [DataMember]
    public virtual Int32? MultiListGroupId { get; set; }

    protected SystemTemplate() { }

    public SystemTemplate(string title, byte[] templateDoc, string templateDocName, TemplateType templateType, int multiListGroupId)
    {
        this.Title = title;
        this.TemplateDoc = templateDoc;
        this.IsSystemTemplate = true;
        this.MultiListGroupId = multiListGroupId;
    }
}

Now, when I try to call following service method:

List<Template> GetTemplatesByTemplateType(int officeId, int? userId, TemplateType templateType)

I get this error:

System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host

Is it because of the reason that I am trying to return an abstract class?
It runs fine if I try to call this method using unit test.

Answer 1

Yes, the problem is your abstract base class which needs to be decorated with the KnownType and XmlInclude attributes. See here: http://geekswithblogs.net/ugandadotnet/archive/2008/05/27/serializing-an-abstract-data-contract.aspx

Answer 2

In addition to grenade's answer about making those descendant classes known to WCF usign the KnownType (or ServiceKnownType) attribute, you'll also have to decorate the descendant classes with a [DataContract] attribute themselves.

[DataContract]
public class UserTemplate : Template
{
    ......
}

[DataContract]
public class SystemTemplate : Template
{
    ......
}

These attributes are almost never inherited from parent to child in WCF - you need to be very explicit and clear about your intent at every level.

Check this blog post All About KnownTypes for more information on the KnownTypes and ServiceKnownTypes attributes.