Question

I’m developing an application that reads data from a SQL server database (migrated from a legacy DB) with nHibernate and s#arp architecture through ADO.NET Data services. I’m trying to map a many-to-many relationship. I have a Error class:

public class Error
{
    public virtual int ERROR_ID { get; set; }
    public virtual string ERROR_CODE { get; set; }
    public virtual string DESCRIPTION { get; set; }

    public virtual IList<ErrorGroup> GROUPS { get; protected set; }
}

And then I have the error group class:

public class ErrorGroup
{
    public virtual int ERROR_GROUP_ID {get; set;}
    public virtual string ERROR_GROUP_NAME { get; set; }
    public virtual string DESCRIPTION { get; set; }

    public virtual IList<Error> ERRORS { get; protected set; }
}

And the overrides:

public class ErrorGroupOverride : IAutoMappingOverride<ErrorGroup>
{
    public void Override(AutoMapping<ErrorGroup> mapping)
    {
        mapping.Table("ERROR_GROUP");
        mapping.Id(x => x.ERROR_GROUP_ID, "ERROR_GROUP_ID");
        mapping.IgnoreProperty(x => x.Id);
        mapping.HasManyToMany<Error>(x => x.Error)
            .Table("ERROR_GROUP_LINK")
            .ParentKeyColumn("ERROR_GROUP_ID")
            .ChildKeyColumn("ERROR_ID").Inverse().AsBag();
    }
}

public class ErrorOverride : IAutoMappingOverride<Error>
{
    public void Override(AutoMapping<Error> mapping)
    {
        mapping.Table("ERROR");
        mapping.Id(x => x.ERROR_ID, "ERROR_ID");
        mapping.IgnoreProperty(x => x.Id);
        mapping.HasManyToMany<ErrorGroup>(x => x.GROUPS)
            .Table("ERROR_GROUP_LINK")
            .ParentKeyColumn("ERROR_ID")
            .ChildKeyColumn("ERROR_GROUP_ID").AsBag();
    }
}

When I view the Data service in the browser like: http://localhost:1905/DataService.svc/Errors it shows the list of errors with no problems, and using it like http://localhost:1905/DataService.svc/Errors(123) works too.

The Problem
When I want to see the Errors in a group or the groups form an error, like: “http://localhost:1905/DataService.svc/Errors(123)?$expand=GROUPS” I get the XML Document, but the browser says:

The XML page cannot be displayed 
Cannot view XML input using XSL style sheet. Please correct the error and then click the Refresh button, or try again later. 
--------------------------------------------------------------------------------
Only one top level element is allowed in an XML document. Error processing resource 'http://localhost:1905/DataServic...
<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
-^

I view the sourcecode, and I get the data. However it comes with an exception:

<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <code></code>
  <message xml:lang="en-US">An error occurred while processing this request.</message>
  <innererror xmlns="xmlns">
    <message>A single resource was expected for the result, but multiple resources were found.</message>

    <type>System.InvalidOperationException</type>
    <stacktrace>   at System.Data.Services.Serializers.Serializer.WriteRequest(IEnumerator queryResults, Boolean hasMoved)&#xD;
   at System.Data.Services.ResponseBodyWriter.Write(Stream stream)</stacktrace>
  </innererror>
</error>

A I missing something??? Where does this error come from?

Answer 1

I think this was due to an error with linq and nHibernate, worked after I restricted the results to return just one.