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How to use ObjectDataSource with ExpandoObject

Environment

Product ProgressĀ® TelerikĀ® Reporting

Description

When binding ObjectDataSource component to a collection of ExpandoObject instances the Reporting engine expects the collection to contain a list of business objects with known properties. As ExpandoObject uses an internal dictionary of string and object (IDictionary) to store the dynamically added properties the engine is not able to find them and throws an error: "The expression contains object 'PropertyName' that is not defined in the current context".

Solution

In order to expose ExpandoObject properties to Reporting engine, a custom TypeDescriptor needs to be provided that will determine the actual properties of the object.

public class ExpandoObjectTypeDescriptionProvider : TypeDescriptionProvider
    {
        private static readonly TypeDescriptionProvider m_Default = TypeDescriptor.GetProvider(typeof(ExpandoObject));
        public ExpandoObjectTypeDescriptionProvider()
            :base(m_Default)
        {
        }
        public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
        {
            var defaultDescriptor = base.GetTypeDescriptor(objectType, instance);
            return instance == null ? defaultDescriptor :
                       new ExpandoObjectTypeDescriptor(instance);
        }
    }
public class ExpandoObjectTypeDescriptor : ICustomTypeDescriptor
    {
        private readonly IDictionary<string,object> m_Instance;
        public ExpandoObjectTypeDescriptor(dynamic instance)
        {
            m_Instance = instance as IDictionary<string, object>;
        }
        public string GetComponentName()
        {
            return TypeDescriptor.GetComponentName(this, true);
        }
        public EventDescriptor GetDefaultEvent()
        {
            return TypeDescriptor.GetDefaultEvent(this, true);
        }
        public string GetClassName()
        {
            return TypeDescriptor.GetClassName(this, true);
        }
        public EventDescriptorCollection GetEvents(Attribute[] attributes)
        {
            return TypeDescriptor.GetEvents(this, attributes, true);
        }
        EventDescriptorCollection ICustomTypeDescriptor.GetEvents()
        {
            return TypeDescriptor.GetEvents(this, true);
        }
        public TypeConverter GetConverter()
        {
            return TypeDescriptor.GetConverter(this, true);
        }
        public object GetPropertyOwner(PropertyDescriptor pd)
        {
            return m_Instance;
        }
        public AttributeCollection GetAttributes()
        {
            return TypeDescriptor.GetAttributes(this, true);
        }
        public object GetEditor(Type editorBaseType)
        {
            return TypeDescriptor.GetEditor(this, editorBaseType, true);
        }
        public PropertyDescriptor GetDefaultProperty()
        {
            return null;
        }
        PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties()
        {
            return ((ICustomTypeDescriptor)this).GetProperties(new Attribute[0]);
        }
        public PropertyDescriptorCollection GetProperties(Attribute[] attributes)
        {
            return new PropertyDescriptorCollection(
                m_Instance.Keys
                          .Select(x => new ExpandoObjectPropertyDescriptor(m_Instance, x))
                          .ToArray<PropertyDescriptor>());
        }
        class ExpandoObjectPropertyDescriptor : PropertyDescriptor
        {
            private readonly IDictionary<string, object> m_Instance;
            private readonly string m_Name;
            public ExpandoObjectPropertyDescriptor(IDictionary<string, object> instance, string name)
                : base(name, null)
            {
                m_Instance = instance;
                m_Name = name;
            }
            public override Type PropertyType
            {
                get { return m_Instance[m_Name].GetType(); }
            }
            public override void SetValue(object component, object value)
            {
                m_Instance[m_Name] = value;
            }
            public override object GetValue(object component)
            {
                return (((IDictionary<string, object>)component))[m_Name];
            }
            public override bool IsReadOnly
            {
                get
                {
                    return false;
                }
            }
            public override Type ComponentType
            {
                get { return null; }
            }
            public override bool CanResetValue(object component)
            {
                return false;
            }
            public override void ResetValue(object component)
            {
            }
            public override bool ShouldSerializeValue(object component)
            {
                return false;
            }
            public override string Category
            {
                get { return string.Empty; }
            }
            public override string Description
            {
                get { return string.Empty; }
            }
        }
    }     

Custom provider can be attached to a single instance or to all instances of ExpandoObject type:

//attach to a single instance
dynamic newObj = new ExpandoObject();
TypeDescriptor.AddProvider(new ExpandoObjectTypeDescriptionProvider(), newObj);
//attach to all instances
TypeDescriptor.AddProvider(new ExpandoObjectTypeDescriptionProvider(), typeof(ExpandoObject));

Suggested Workarounds

In case if you want to add a second data item with a second list of ExpandoObjects (having different properties) it shows error: "The expression contains object 'ProperyName' that is not defined in the current context." on the second one.

Note that the Telerik Reporting engine expects the ObjectDataSource collection to include a list of business objects with known properties and there is no out-of-the-box functionality to contain collection of ExpandoObject. So, only the first ExpandoObject properties that are added to a collection would be available in the report to feed the ObjectDataSource.

However, the possible workaround is available by following these steps:

  1. Create one ExpandoObject with all properties that would be used later in the report;
  2. Add it to a collection (make sure that it is the first item in the collection);
  3. Register the ExpandoObject type in the application Main method using the following code:
TypeDescriptor.AddProvider(new ExpandoObjectTypeDescriptionProvider(), typeof(ExpandoObject));
  1. Bind an ObjectDataSource to the created collection from step 2;
  2. In the report create a Data Item with property Visible = false;
  3. Set the DataSource of the hidden data item to be the newly created ObjectDataSource.
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