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Creating a dynamic, extensible C# Expando Object


I love dynamic functionality in a strongly typed language because it offers us the best of both worlds. In C# (or any of the main .NET languages) we now have the dynamic type that provides a host of dynamic features for the static C# language.

One place where I've found dynamic to be incredibly useful is in building extensible types or types that expose traditionally non-object data (like dictionaries) in easier to use and more readable syntax. I wrote about a couple of these for accessing old school ADO.NET DataRows and DataReaders more easily for example. These classes are dynamic wrappers that provide easier syntax and auto-type conversions which greatly simplifies code clutter and increases clarity in existing code.

ExpandoObject in .NET 4.0

Another great use case for dynamic objects is the ability to create extensible objects - objects that start out with a set of static members and then can add additional properties and even methods dynamically. The .NET 4.0 framework actually includes an ExpandoObject class which provides a very dynamic object that allows you to add properties and methods on the fly and then access them again.

For example with ExpandoObject you can do stuff like this:

dynamic expand = new ExpandoObject();

expand.Name = "Rick";
expand.HelloWorld = (Func<string, string>) ((string name) => 
{ 
    return "Hello " + name; 
});

Console.WriteLine(expand.Name);
Console.WriteLine(expand.HelloWorld("Dufus"));

Internally ExpandoObject uses a Dictionary like structure and interface to store properties and methods and then allows you to add and access properties and methods easily. As cool as ExpandoObject is it has a few shortcomings too:

  • It's a sealed type so you can't use it as a base class
  • It only works off 'properties' in the internal Dictionary - you can't expose existing type data
  • It doesn't serialize to XML or with DataContractSerializer/DataContractJsonSerializer

Expando - A truly extensible Object

ExpandoObject is nice if you just need a dynamic container for a dictionary like structure. However, if you want to build an extensible object that starts out with a set of strongly typed properties and then allows you to extend it, ExpandoObject does not work because it's a sealed class that can't be inherited.

I started thinking about this very scenario for one of my applications I'm building for a customer. In this system we are connecting to various different user stores. Each user store has the same basic requirements for username, password, name etc. But then each store also has a number of extended properties that is available to each application. In the real world scenario the data is loaded from the database in a data reader and the known properties are assigned from the known fields in the database. All unknown fields are then 'added' to the expando object dynamically.

In the past I've done this very thing with a separate property - Properties - just like I do for this class. But the property and dictionary syntax is not ideal and tedious to work with.

I started thinking about how to represent these extra property structures. One way certainly would be to add a Dictionary, or an ExpandoObject to hold all those extra properties. But wouldn't it be nice if the application could actually extend an existing object that looks something like this as you can with the Expando object:

public class User : Westwind.Utilities.Dynamic.Expando
{
    public string Email { get; set; }
    public string Password { get; set; }
    public string Name { get; set; }
    public bool Active { get; set; }
    public DateTime? ExpiresOn { get; set; }
}

and then simply start extending the properties of this object dynamically? Using the Expando object I describe later you can now do the following:

[TestMethod]
public void UserExampleTest()
{            
    var user = new User();

    // Set strongly typed properties
    user.Email = "rick@west-wind.com";
    user.Password = "nonya123";
    user.Name = "Rickochet";
    user.Active = true;

    // Now add dynamic properties
    dynamic duser = user;
    duser.Entered = DateTime.Now;
    duser.Accesses = 1;

    // you can also add dynamic props via indexer
    user["NickName"] = "AntiSocialX";
    duser["WebSite"] = "http://www.west-wind.com/weblog";


    // Access strong type through dynamic ref
    Assert.AreEqual(user.Name,duser.Name);

    // Access strong type through indexer 
    Assert.AreEqual(user.Password,user["Password"]);
    

    // access dyanmically added value through indexer
    Assert.AreEqual(duser.Entered,user["Entered"]);
    
    // access index added value through dynamic
    Assert.AreEqual(user["NickName"],duser.NickName);
    

    // loop through all properties dynamic AND strong type properties (true)
    foreach (var prop in user.GetProperties(true))
    { 
        object val = prop.Value;
        if (val == null)
            val = "null";

        Console.WriteLine(prop.Key + ": " + val.ToString());
    }
}

As you can see this code somewhat blurs the line between a static and dynamic type. You start with a strongly typed object that has a fixed set of properties. You can then cast the object to dynamic (as I discussed in my last post) and add additional properties to the object. You can also use an indexer to add dynamic properties to the object.

To access the strongly typed properties you can use either the strongly typed instance, the indexer or the dynamic cast of the object. Personally I think it's kinda cool to have an easy way to access strongly typed properties by string which can make some data scenarios much easier.

To access the 'dynamically added' properties you can use either the indexer on the strongly typed object, or property syntax on the dynamic cast.

Using the dynamic type allows all three modes to work on both strongly typed and dynamic properties.

Finally you can iterate over all properties, both dynamic and strongly typed if you chose. Lots of flexibility.

Note also that by default the Expando object works against the (this) instance meaning it extends the current object. You can also pass in a separate instance to the constructor in which case that object will be used to iterate over to find properties rather than this.

Using this approach provides some really interesting functionality when use the dynamic type. To use this we have to add an explicit constructor to the Expando subclass:

public class User : Westwind.Utilities.Dynamic.Expando
{
    public string Email { get; set; }
    public string Password { get; set; }
    public string Name { get; set; }
    public bool Active { get; set; }
    public DateTime? ExpiresOn { get; set; }

    public User() : base()
    { }

    // only required if you want to mix in seperate instance
    public User(object instance)
        : base(instance)
    {
    }
}

to allow the instance to be passed. When you do you can now do:

[TestMethod]
public void ExpandoMixinTest()
{
    // have Expando work on Addresses
    var user = new User( new Address() );

    // cast to dynamicAccessToPropertyTest
    dynamic duser = user;

    // Set strongly typed properties
    duser.Email = "rick@west-wind.com";
    user.Password = "nonya123";
    
    // Set properties on address object
    duser.Address = "32 Kaiea";
    //duser.Phone = "808-123-2131";

    // set dynamic properties
    duser.NonExistantProperty = "This works too";

    // shows default value Address.Phone value
    Console.WriteLine(duser.Phone);

}


Using the dynamic cast in this case allows you to access *three* different 'objects': The strong type properties, the dynamically added properties in the dictionary and the properties of the instance passed in! Effectively this gives you a way to simulate multiple inheritance (which is scary - so be very careful with this, but you can do it).

How Expando works

Behind the scenes Expando is a DynamicObject subclass as I discussed in my last post. By implementing a few of DynamicObject's methods you can basically create a type that can trap 'property missing' and 'method missing' operations. When you access a non-existant property a known method is fired that our code can intercept and provide a value for. Internally Expando uses a custom dictionary implementation to hold the dynamic properties you might add to your expandable object.

Let's look at code first. The code for the Expando type is straight forward and given what it provides relatively short. Here it is.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Dynamic;
using System.Reflection;

namespace Westwind.Utilities.Dynamic
{
    /// <summary>
    /// Class that provides extensible properties and methods. This
    /// dynamic object stores 'extra' properties in a dictionary or
    /// checks the actual properties of the instance.
    /// 
    /// This means you can subclass this expando and retrieve either
    /// native properties or properties from values in the dictionary.
    /// 
    /// This type allows you three ways to access its properties:
    /// 
    /// Directly: any explicitly declared properties are accessible
    /// Dynamic: dynamic cast allows access to dictionary and native properties/methods
    /// Dictionary: Any of the extended properties are accessible via IDictionary interface
    /// </summary>
    [Serializable]
    public class Expando : DynamicObject, IDynamicMetaObjectProvider
    {
        /// <summary>
        /// Instance of object passed in
        /// </summary>
        object Instance;

        /// <summary>
        /// Cached type of the instance
        /// </summary>
        Type InstanceType;

        PropertyInfo[] InstancePropertyInfo
        {
            get
            {
                if (_InstancePropertyInfo == null && Instance != null)                
                    _InstancePropertyInfo = Instance.GetType().GetProperties(BindingFlags.Instance |                                                           BindingFlags.Public | BindingFlags.DeclaredOnly);
                return _InstancePropertyInfo;                
            }
        }
        PropertyInfo[] _InstancePropertyInfo;


        /// <summary>
        /// String Dictionary that contains the extra dynamic values
        /// stored on this object/instance
        /// </summary>        
        /// <remarks>Using PropertyBag to support XML Serialization of the dictionary</remarks>
        public PropertyBag Properties = new PropertyBag();

        //public Dictionary<string,object> Properties = new Dictionary<string, object>();

        /// <summary>
        /// This constructor just works off the internal dictionary and any 
        /// public properties of this object.
        /// 
        /// Note you can subclass Expando.
        /// </summary>
        public Expando() 
        {
            Initialize(this);            
        }

        /// <summary>
        /// Allows passing in an existing instance variable to 'extend'.        
        /// </summary>
        /// <remarks>
        /// You can pass in null here if you don't want to 
        /// check native properties and only check the Dictionary!
        /// </remarks>
        /// <param name="instance"></param>
        public Expando(object instance)
        {
            Initialize(instance);
        }


        protected virtual void Initialize(object instance)
        {
            Instance = instance;
            if (instance != null)
                InstanceType = instance.GetType();           
        }


       /// <summary>
       /// Try to retrieve a member by name first from instance properties
       /// followed by the collection entries.
       /// </summary>
       /// <param name="binder"></param>
       /// <param name="result"></param>
       /// <returns></returns>
        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            result = null;

            // first check the Properties collection for member
            if (Properties.Keys.Contains(binder.Name))
            {
                result = Properties[binder.Name];
                return true;
            }


            // Next check for Public properties via Reflection
            if (Instance != null)
            {
                try
                {
                    return GetProperty(Instance, binder.Name, out result);                    
                }
                catch { }
            }

            // failed to retrieve a property
            result = null;
            return false;
        }


        /// <summary>
        /// Property setter implementation tries to retrieve value from instance 
        /// first then into this object
        /// </summary>
        /// <param name="binder"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        public override bool TrySetMember(SetMemberBinder binder, object value)
        {

            // first check to see if there's a native property to set
            if (Instance != null)
            {
                try
                {
                    bool result = SetProperty(Instance, binder.Name, value);
                    if (result)
                        return true;
                }
                catch { }
            }
            
            // no match - set or add to dictionary
            Properties[binder.Name] = value;
            return true;
        }

        /// <summary>
        /// Dynamic invocation method. Currently allows only for Reflection based
        /// operation (no ability to add methods dynamically).
        /// </summary>
        /// <param name="binder"></param>
        /// <param name="args"></param>
        /// <param name="result"></param>
        /// <returns></returns>
        public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
        {
            if (Instance != null)
            {
                try
                {
                    // check instance passed in for methods to invoke
                    if (InvokeMethod(Instance, binder.Name, args, out result))
                        return true;                    
                }
                catch { }
            }

            result = null;
            return false;
        }
        

        /// <summary>
        /// Reflection Helper method to retrieve a property
        /// </summary>
        /// <param name="instance"></param>
        /// <param name="name"></param>
        /// <param name="result"></param>
        /// <returns></returns>
        protected bool GetProperty(object instance, string name, out object result)
        {
            if (instance == null)
                instance = this;

            var miArray = InstanceType.GetMember(name, BindingFlags.Public |                                       BindingFlags.GetProperty | BindingFlags.Instance);
            if (miArray != null && miArray.Length > 0)
            {
                var mi = miArray[0];
                if (mi.MemberType == MemberTypes.Property)
                {
                    result = ((PropertyInfo)mi).GetValue(instance,null);
                    return true;
                }
            }

            result = null;
            return false;                
        }

        /// <summary>
        /// Reflection helper method to set a property value
        /// </summary>
        /// <param name="instance"></param>
        /// <param name="name"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        protected bool SetProperty(object instance, string name, object value)
        {
            if (instance == null)
                instance = this;

            var miArray = InstanceType.GetMember(name, BindingFlags.Public |                                                        BindingFlags.SetProperty |                                                        BindingFlags.Instance);
            if (miArray != null && miArray.Length > 0)
            {
                var mi = miArray[0];
                if (mi.MemberType == MemberTypes.Property)
                {
                    ((PropertyInfo)mi).SetValue(Instance, value, null);
                    return true;
                }
            }
            return false;                
        }

        /// <summary>
        /// Reflection helper method to invoke a method
        /// </summary>
        /// <param name="instance"></param>
        /// <param name="name"></param>
        /// <param name="args"></param>
        /// <param name="result"></param>
        /// <returns></returns>
        protected bool InvokeMethod(object instance, string name, object[] args, out object result)
        {
            if (instance == null)
                instance = this;

            // Look at the instanceType
            var miArray = InstanceType.GetMember(name,
                                    BindingFlags.InvokeMethod |
                                    BindingFlags.Public | BindingFlags.Instance);

            if (miArray != null && miArray.Length > 0)
            {
                var mi = miArray[0] as MethodInfo;
                result = mi.Invoke(Instance, args);
                return true;
            }

            result = null;
            return false;
        }



        /// <summary>
        /// Convenience method that provides a string Indexer 
        /// to the Properties collection AND the strongly typed
        /// properties of the object by name.
        /// 
        /// // dynamic
        /// exp["Address"] = "112 nowhere lane"; 
        /// // strong
        /// var name = exp["StronglyTypedProperty"] as string; 
        /// </summary>
        /// <remarks>
        /// The getter checks the Properties dictionary first
        /// then looks in PropertyInfo for properties.
        /// The setter checks the instance properties before
        /// checking the Properties dictionary.
        /// </remarks>
        /// <param name="key"></param>
        /// 
        /// <returns></returns>
        public object this[string key]
        {
            get
            {
                try
                {
                    // try to get from properties collection first
                    return Properties[key];
                }
                catch (KeyNotFoundException ex)
                {
                    // try reflection on instanceType
                    object result = null;
                    if (GetProperty(Instance, key, out result))
                        return result;

                    // nope doesn't exist
                    throw;
                }
            }
            set
            {
                if (Properties.ContainsKey(key))
                {
                    Properties[key] = value;
                    return;
                }

                // check instance for existance of type first
                var miArray = InstanceType.GetMember(key, BindingFlags.Public | BindingFlags.GetProperty);
                if (miArray != null && miArray.Length > 0)
                    SetProperty(Instance, key, value);
                else
                    Properties[key] = value;
            }
        }


        /// <summary>
        /// Returns and the properties of 
        /// </summary>
        /// <param name="includeProperties"></param>
        /// <returns></returns>
        public IEnumerable<KeyValuePair<string,object>> GetProperties(bool includeInstanceProperties = false)
        {
            if (includeInstanceProperties && Instance != null)
            {
                foreach (var prop in this.InstancePropertyInfo)
                    yield return new KeyValuePair<string, object>(prop.Name, prop.GetValue(Instance, null));
            }

            foreach (var key in this.Properties.Keys)
               yield return new KeyValuePair<string, object>(key, this.Properties[key]);

        }
  

        /// <summary>
        /// Checks whether a property exists in the Property collection
        /// or as a property on the instance
        /// </summary>
        /// <param name="item"></param>
        /// <returns></returns>
        public bool Contains(KeyValuePair<string, object> item, bool includeInstanceProperties = false)
        {
            bool res = Properties.ContainsKey(item.Key);
            if (res)
                return true;

            if (includeInstanceProperties && Instance != null)
            {
                foreach (var prop in this.InstancePropertyInfo)
                {
                    if (prop.Name == item.Key)
                        return true;
                }
            }

            return false;
        }        

    }
}

Although the Expando class supports an indexer, it doesn't actually implement IDictionary or even IEnumerable. It only provides the indexer and Contains() and GetProperties() methods, that work against the Properties dictionary AND the internal instance.

The reason for not implementing IDictionary is that a) it doesn't add much value since you can access the Properties dictionary directly and that b) I wanted to keep the interface to class very lean so that it can serve as an entity type if desired. Implementing these IDictionary (or even IEnumerable) causes LINQ extension methods to pop up on the type which obscures the property interface and would only confuse the purpose of the type. IDictionary and IEnumerable are also problematic for XML and JSON Serialization - the XML Serializer doesn't serialize IDictionary<string,object>, nor does the DataContractSerializer. The JavaScriptSerializer does serialize, but it treats the entire object like a dictionary and doesn't serialize the strongly typed properties of the type, only the dictionary values which is also not desirable. Hence the decision to stick with only implementing the indexer to support the user["CustomProperty"] functionality and leaving iteration functions to the publicly exposed Properties dictionary.

Note that the Dictionary used here is a custom PropertyBag class I created to allow for serialization to work. One important aspect for my apps is that whatever custom properties get added they have to be accessible to AJAX clients since the particular app I'm working on is a SIngle Page Web app where most of the Web access is through JSON AJAX calls. PropertyBag can serialize to XML and one way serialize to JSON using the JavaScript serializer (not the DCS serializers though).

The key components that make Expando work in this code are the Properties Dictionary and the TryGetMember() and TrySetMember() methods. The Properties collection is public so if you choose you can explicitly access the collection to get better performance or to manipulate the members in internal code (like loading up dynamic values form a database).

Notice that TryGetMember() and TrySetMember() both work against the dictionary AND the internal instance to retrieve and set properties. This means that user["Name"] works against native properties of the object as does user["Name"] = "RogaDugDog".

What's your Use Case?

This is still an early prototype but I've plugged it into one of my customer's applications and so far it's working very well. The key features for me were the ability to easily extend the type with values coming from a database and exposing those values in a nice and easy to use manner. I'm also finding that using this type of object for ViewModels works very well to add custom properties to view models. I suspect there will be lots of uses for this - I've been using the extra dictionary approach to extensibility for years - using a dynamic type to make the syntax cleaner is just a bonus here.

What can you think of to use this for?

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Feedback for this Post

 
# re: Creating a dynamic, extensible C# Expando Object
by John Atten February 08, 2012 @ 4:48am
Fantastic post! Thanks.

I am having to learn all this on my own, and this is exactly the kin thing I find most helpful. Helps me understand what happens "inside the black box" so to speak.

What would I use this for? I'll get back to you after I have mastered it a little.

#Subscribed. :-)
# re: Creating a dynamic, extensible C# Expando Object
by Mark February 08, 2012 @ 7:30am
Great article Rick, IMHO dynamics are convenient, but not much more than that. I sometimes dynamically add when using Javascript, but I don't see the trade off of the convenience versus power (losing LINQ like stuff).

A similar case can be made for the recent trend of NoSQL, yes it has it's place, but I believe it is more niche cases when considering the need "dynamically" add properties on certain objects. A good model done from the get-go is a better approach.

Convenient - yes, practical - no. I'd be interested to hear other use-cases, maybe I'm missing some good functionality that can be done with dynamics.
# re: Creating a dynamic, extensible C# Expando Object
by Bertrand Le Roy February 08, 2012 @ 11:20am
Rick, did you check out Clay? http://clay.codeplex.com/ That's what we use in Orchard for all our dynamic object needs (and we have a lot). It's very extensible and has fantastic object initialization syntax.
# re: Creating a dynamic, extensible C# Expando Object
by Rick Strahl February 08, 2012 @ 12:56pm
@Bertrand - I started to but didn't get around to playing with it yet - this post was already written up :-). Did see your post on it though and will definitely take a closer look when I get a chance.
# re: Creating a dynamic, extensible C# Expando Object
by Rick Strahl February 08, 2012 @ 1:03pm
@Mark - I don't agree that dynamics are more than a niche. I think with a static language you tend to make yourself think about problems in a rigid non-changing fashion with things like ORMs and other auto-mapping tools. While it's possible to extend these (with dictionaries for example), the syntax is often undesirable and requires special code to manage the extra data. Dynamics can make that code more natural and take away some of the tedium like type casting that you otherwise have to do. The downside is that dynamic data has a bit of overhead although for things like dictionaries it's not too bad.
# re: Creating a dynamic, extensible C# Expando Object
by ms440 February 09, 2012 @ 1:10am
@Rick. Thanks!

Great article as always. I used Clay (tnx to Bertrand and his team), but in my latest project I'm trying ImpromptuInterface (take a look at http://code.google.com/p/impromptu-interface/) it is much faster and, while not as rich as Clay (IMHO), gives me the functionality I really need in my project.
# re: Creating a dynamic, extensible C# Expando Object
by Jim Z. February 09, 2012 @ 11:02am
Can you explain a little more about using the new constructor, passing in "new Address()"? Reading the code it looked like Address was a class (defined elsewhere I guess), and this created a Property on User called Address. But the code uses Address as just a string. I was expecting something like duser.Address.City = "Maui" or something like that, where the Address class had a City property. I'm confused.
# re: Creating a dynamic, extensible C# Expando Object
by SciFi Geek February 09, 2012 @ 1:51pm
What kind of data store and data access technology are you using with these Expandos?
# re: Creating a dynamic, extensible C# Expando Object
by Rick Strahl February 09, 2012 @ 4:05pm
@Jim - The constructor supports an object instance that can be passed in. Basically that object's properties become available on the dynamic type. So if you Address with properties of StreetAddress, Phone you can do:

Address address = new Address();
address.StreetAddress  = "New Street Address";
 
dynamic user = new User( address );
 
// static property of User class
string name = user.Name;  
 
// static property of Address class
string street = user.StreetAddress;    // "New Street Address"


In essence you can mix-in a second type into your object data - the properties are effectively merged.

The order is:
* Native strong type properties are loaded first (by the DLR)
* Dynamically added properties are loaded next (by DynamicObject overrides)
* Instance properties are loaded last

In theory this could be expanded to mix in a bunch of objects that are checked for properties and extend the original type.

This is a bit like jQuery.extend() which merges two types into one.
# re: Creating a dynamic, extensible C# Expando Object
by Jamie February 10, 2012 @ 9:44am
I got into this a bit myself, actually while writing a C# version of JQuery.extend() but I could never quite resolve one issue and was wondering if your experience could shed some light on this. (Detailed info on the internals of dynamic types seems tough to come by on the web!)

The GetMemberBinder parameter returned by TryGetMember has this property "ReturnType" which would seem to be extraordinarily useful, if it would let you know at run time the type of the target of the assignment. In practice it seems to always return "object". The only thing I could find about this is that it has to do with complexities of the CLR and the code can't find out the return type at that point in the execution for reasons I did not quite understand.

Is there any way to determine at run time the target type of an expando object Get? This would let you do miraculous things like:

dynamic test = new ExpandoObject();
test.stringVal = "12";
int intVal = test.stringVal;


Which, unfortunately, will fail at runtime (with the native ExpandoObject anyway). This means that in practice, I can't use the best part of dynamics sometimes, since the whole reason for using them in the first place is, er, to deal with stuff you don't know about. At least for me - I use them pretty much exclusively for dealing with data from javascript/JSON.

So I've resorted to implementing a DynamicObject with a Get<T> method and coding this like:

int intVal = test.Get<int>("stringVal");  // or


Which, of course, kind of defeats the purpose in my mind, if I have to substitute a lot of ugly type conversion code for creating a lot of single use classes.
# re: Creating a dynamic, extensible C# Expando Object
by Rick Strahl February 13, 2012 @ 1:38am
@Jamie - Ah I see what you're trying to do. The issue is that the runtime binder doesn't know what to bind to until the value comes back. I think custom implementations of IDynamicMetaObject can potentially provide the target type, but DynamicObject doesn't provide it.

Type conversions should work however if .NET supports implicit conversions. Casting from int to decimal for example should work.

This works:
dynamic intVal = 10;
decimal decVal = intVal;
Console.WriteLine(decVal);

But this doesn't:

dynamic intVal = 10;
string stringVal = intVal;
Console.WriteLine(stringVal);

because it's an explicit conversion from int to string. You should be able to do things like direct assignments to an interface or parent class without problems as well.

So, what's the use case with this? This is one thing I would rather avoid. I know you can do this in JavaScript and most other true dynamic languages, but that's one feature that's not desirable IMHO. And if you are using explicit conversions then I think you should also be explicit in your conversion code.
# re: Creating a dynamic, extensible C# Expando Object
by Marty August 07, 2012 @ 6:54am
Hi,

Speaking of use case`s, what I'm trying to do is create a Dynamic Contact list.
That has a strongly typed base class "Contact" with props like Name, Sex, Phone
and a "Profile" class, that has props like ContactId, PropName, PropVal to enable storage of unlimited number of Contact attributes.

Your approach seems to be a good start for a POCO class, that would later on map to the described entity structure.

My question is - How do You think, would it be possible to achieve a reasonable result that would allow querying those dynamic properties, so it woul look like this :

DynamicContact.Where(p=>p.SomeProperty = "1" && p.SomeOtherProperty = 5)
# re: Creating a dynamic, extensible C# Expando Object
by Boris B. September 15, 2012 @ 6:39am
Nice, I've been searching for a generic way to create ViewModels that extend base models with additional properties and behavior when this blog came up.

A suggestion, why not make your Expando generic, as in Expando<TBase>, that way you can store PropertyInfo[] and such in a static field (in a generic class each closed type would gets it's separate static), since property and method infos should be same for all instances of the same base object type? Then you could replace every GetType() with typeof(TBase) which would then resolve the type at compiletime.

And a question, does this work with existing databinding mechanisms for WPF and/or WinForms, i.e. could you stuff this Expando in a BindingSource and bind controls to that BindingSource (and use those new, dynamic properties)?
# re: Creating a dynamic, extensible C# Expando Object
by Rick Strahl October 22, 2012 @ 2:57pm
@Boris - Databinding unfortunately can be problematic. I haven't tried with WPF or WinForms but I suspect it won't because they use Reflection to pick up properties and don't look at the dynamic type interfaces that provide the properties. That's definitely a limitation.
# re: Creating a dynamic, extensible C# Expando Object
by David P. January 18, 2013 @ 6:54am
This was an interesting article, but my use case is similar to Marty's. I started out by using the dbContext generator for persistent ignorant entity classes for my Database tables. I have a fluctuating amount on extended properties that can be known at runtime by doing a db lookup. For data retrieval I have a stored proc that does a dynamic PIVOT to retrun a crosstab resultset, with all these extendable columns in it. I would like to get a List of these returned, such as:

ExtendBaseClass(typeof(MyTable));
List<MyTableExtended> lList = dbContext.Database.SqlQuery<MyTableExtended>("EXEC spGetMyTable @Param1,new SqlParameter { ParameterName = "Param1", DbType = System.Data.DbType.String, Value = "Bob" }).ToList<MyTableExtended>();
 
public void ExtendBaseClass(Type baseClass)
{
      // Run code to add extended properties
}


Is something like this possible?

:) David
# re: Creating a dynamic, extensible C# Expando Object
by Peter January 31, 2013 @ 1:23pm
Hi Rick,

Cool article. Thanks!

I have a question about JSON serialization of the Expando from ASP.NET. When using a default webmethod and json serialization the result after serializing is <variable>.Properties.<property_A>.
However when using it in javascript, the existence of the Properties intermediate property is not really useful. What are your thoughts on "getting rid of it" when serializing to JSON?

Thank you,

Peter
# re: Creating a dynamic, extensible C# Expando Object
by Rick Strahl January 31, 2013 @ 1:41pm
@Peter - I think you should be able to do [XmlIgnore][NonSerialized] combo to have the JSON serializers ignore it. Haven't tried this though. But... wouldn't you want the properties? How else would this object serialize, since all state is in the properties dictionary?
 


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