Object Data Source with Reporting Services in Visual Studio - asp.net

Question

I'm working on a site where we want to include a pie chart on a page. Right now I'm working on implementing that through Reporting Services (RDLC file) with an object data source.
The SelectMethod of my object data source is a method that returns a list of business objects; lets say a List<Alpha> and Alpha has a sub object Beta with a Name property. In my report definition I have set the Category groups to be: =Fields!Beta.Value.Name this means that Alpha.Beta.Name are my pie slices. I got the following error:
An error has occurred during report processing. The Group expression for the grouping 'chart1_CategoryGroup1' contains an error: Object variable or With block variable not set.
I was able to confirm this is because Beta is nullable and was able to fix the issue by updating the object Alpha to return a new Beta() if the Beta property is null. This solution is not ideal though because there are other places in my code where I need Beta to be null if it doesn't have a value yet.
Is there a way to update the report definition to accept a null property as valid? Ideally I would like to specify the value as "Not Set" if Beta is null.

Answer 1

I had similar problem as yours, and I solved it using Null Object Refactoring ( many thanks to Martin Fowler's book Refactoring :)).
Here you can find nice example Null object refactoring
So you could create class NullableBeta that inherits Beta, while properties Name and e.g. IsNullable are virtual on Beta entity.
public class Beta
{
public virtual Name{ get; set;}
public virtual IsSet{ get{return true;}}
}
public class NullableBeta:Beta
{
public override Name
{
get{
return "Not Set";
}
set{}
}
public override IsSet{ get{ return false;}}
}
Now, if Beta is not set on Alfa entity, you could return instance of NullableBeta entity. In reports, you would have "Not Set" instead of empty string, and on places where you are setting Beta entity to Alfa you can check IsSet property instead of checking if Beta is null.
Hope this was helpful

Answer 2

I had similar problem as yours, and I solved it using Null Object Refactoring ( many thanks to Martin Fowler's book Refactoring :)). Here you can find nice example Null object refactoring
I first deal with this shortcomings of SSRS/RDLC by implementing the Null object pattern as well.
Implementing this manually is of course too much effort when more then one or two domain objects are involved.
However, since I am already using AutoMapper, #LucianBargaoanu correctly pointed out in the comments that null objects are natively supported as an opt-in feature by AutoMapper, so there is no explicit implementation needed.
I therefore use AutoMapper with its AllowNullDestinationValues, AllowNullCollections, PreserveReferences(), NullSubstitute and ForAllPropertyMaps() features, to map all my domain classes to report specific classes and substitute all null references to either null objects (when mapping domain object null references to report objects) or reasonable default values (e.g. an empty string for null strings or the default value of the underlying primitive type for Nullable<PrimitiveType>).
Here is some sample code to demonstrate the approach:
namespace Domain
{
public class MyClass
{
public int Id {get; set;}
public string Name {get; set;} // could be null
public string Code {get; set;} // could be null
public decimal? SomeNullableValue {get; set;} // could be null
public MyOtherClass OptionalOtherClass {get; set;} // could be null
}
public class MyOtherClass
{
public int OtherId {get; set;}
public string OtherName {get; set;} // could be null
public decimal? SomeOtherNullableValue {get; set;} // could be null
}
}
namespace ReportViewModels
{
[Serializable]
public class MyClass
{
public int Id {get; set;}
public string Name {get; set;} // should not be null (but empty)
public string Code {get; set;} // should not be null (but empty)
public decimal? SomeNullableValue {get; set;} // should not be null (but default(decimal))
public string CommonName
=> (Name + " " + Code).Trim();
public MyOtherClass OptionalOtherClass {get; set;} // should not be null (but a MyOtherClass null object)
}
[Serializable]
public class MyOtherClass
{
public int OtherId {get; set;}
public string OtherName {get; set;} // should not be null (but empty)
public decimal? SomeOtherNullableValue {get; set;} // should not be null (but default(decimal))
}
}
public partial class Form1 : Form
{
private Context _context;
private ReportObjectGenerator _reportObjectGenerator;
public Form1(Context context, ReportObjectGenerator reportObjectGenerator)
{
_context = context;
_reportObjectGenerator = reportObjectGenerator;
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
var myDomainObjects = context.MyClass
.Include(e => e.OptionalOtherClass)
.ToList();
var myReportViewModels = _reportObjectGenerator.GetReportObjects<Domain.MyClass, ReportViewModels.MyClass>(myDomainObjects);
components ??= new System.ComponentModel.Container();
//reportViewer1.LocalReport.ReportEmbeddedResource = "MyNamespace.Report1.rdlc";
reportViewer1.LocalReport.ReportPath = "Report1.rdlc";
reportViewer1.LocalReport.DataSources.Clear();
reportViewer1.LocalReport.DataSources.Add(
new ReportDataSource
{
Name = "MyClassDataSet",
Value = new BindingSource(components)
{
DataMember = "MyClass",
DataSource = myReportViewModels
}
});
reportViewer1.RefreshReport();
}
}
public class ReportObjectGenerator
{
public List<TDestination> GetReportObjects<TSource, TDestination>(
IEnumerable<TSource> sourceObjects)
{
var domainNamespace = typeof(TSource).Namespace ?? throw new InvalidOperationException();
var reportNamespace = typeof(TDestination).Namespace ?? throw new InvalidOperationException();
var mapper = new MapperConfiguration(
cfg =>
{
cfg.AllowNullDestinationValues = false;
cfg.AllowNullCollections = false;
var allTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(a => a.GetTypes()).ToList();
var allDomainTypes = allTypes.Where(t => t.Namespace?.StartsWith(domainNamespace) ?? false).ToList();
var allReportTypes = allTypes.Where(t => t.Namespace?.StartsWith(reportNamespace) ?? false).ToList();
foreach (var reportClassType in allReportTypes)
{
var domainClassType = allDomainTypes.Single(t => t.Name == reportClassType.Name);
cfg.CreateMap(domainClassType, reportClassType)
.PreserveReferences();
}
// If we want to set the default value of the underlying type of Nullable<UnderlyingType>
// properties in case they would be null, than AllowNullDestinationValues is not enough and we
// need to manually replace the null value here.
cfg.ForAllPropertyMaps(
pm => pm.SourceMember.GetMemberType().IsNullableType(),
(p, _) => p.NullSubstitute ??= Activator.CreateInstance(p.SourceMember.GetMemberType().GetTypeOfNullable()));
})
.CreateMapper();
return mapper.Map<IEnumerable<TSource>, List<TDestination>>(sourceObjects);
}
}