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Routing an object in C# without using switch statements

I am writing a piece of software in c# .net 4.0 and am running into a wall in making sure that the code-base is extensible, re-usable and flexible in a particular area.
We have data coming into it that needs to be broken down in discrete organizational units. These units will need to be changed, sorted, deleted, and added to as the company grows.
No matter how we slice the data structure we keep running into a boat-load of conditional statements (upwards of 100 or so to start) that we are trying to avoid, allowing us to modify the OUs easily.
We are hoping to find an object-oriented method that would allow us to route the object to different workflows based on properties of that object without having to add switch statements every time.
So, for example, let's say I have an object called "Order" come into the system. This object has 'orderItems' inside of it. Each of those different kinds of 'orderItems' would need to fire a different function in the code to be handled appropriately. Each 'orderItem' has a different workflow. The conditional looks basically like this -
if(order.orderitem == 'photo')
{do this}
else if(order.orderitem == 'canvas')
{do this}
edit: Trying to clarify.

I'm not sure your question is very well defined, you need a lot more specifics here - a sample piece of data, sample piece of code, what have you tried...
No matter how we slice the data structure we keep running into a boat-load of conditional statements (upwards of 100 or so to start) that we are trying to avoid
This usually means you're trying to encode data in your code - just add a data field (or a few).
Chances are your ifs are linked to each other, it's hard to come up with 100 independent ifs - that would imply you have 100 independent branches for 100 independent data conditions. I haven't encountered such a thing in my career that really would require hard-coding 100 ifs.
Worst case scenario you can make an additional data field contain a config file or even a script of your choice. Either case - your data is incomplete if you need 100 ifs
With the update you've put in your question here's one simple approach, kind of low tech. You can do better with dependency injection and some configuration but that can get excessive too, so be careful:
public class OrderHandler{
public static Dictionary<string,OrderHandler> Handlers = new Dictionary<string,OrderHandler>(){
{"photo", new PhotoHandler()},
{"canvas", new CanvasHandler()},
};
public virtual void Handle(Order order){
var handler = handlers[order.OrderType];
handler.Handle(order);
}
}
public class PhotoHandler: OrderHandler{...}
public class CanvasHandler: OrderHandler{...}

What you could do is called - "Message Based Routing" or "Message Content Based" Routing - depending on how you implement it.
In short, instead of using conditional statements in your business logic, you should implement organizational units to look for the messages they are interested in.
For example:
Say your organization has following departments - "Plant Products", "Paper Products", "Utilities". Say there is only one place where the orders come in - Ordering (module).
here is a sample incoming message.
Party:"ABC Cop"
Department: "Plant Product"
Qty: 50
Product: "Some plan"
Publish out a message with this information. In the module that processes orders for "Plant Products" configure it such that it listens to a message that has "Department = Plant Products". This way, you push the onus on the department modules instead of on the main ordering module.
You can do this using NServiceBus, BizTalk, or any other ESB you might already have.
This is how you do in BizTalk and this is how you can do in NServiceBus

Have you considered sub-typing OrderItem?
public class PhotoOrderItem : OrderItem {}
public class CanvasOrderItem : OrderItem {}
Another option would be to use the Strategy pattern. Add an extra property to your OrderItem class definition for the OrderProcessStrategy and use a PhotoOrderStrategy/CanvasOrderStrategy to contain all of the different logic.
public class OrderItem{
public IOrderItemStrategy Strategy;
}
public interface IOrderItemStrategy{
public void Checkout();
public Control CheckoutStub{get;}
public bool PreCheckoutValidate();
}
public class PhotoOrderStrategy : IOrderItemStrategy{}
public class CanvasOrderStrategy : IOrderItemStrategy{}

Taking the specific example:
You could have some Evaluator that takes an order and iterates each line item. Instead of processing if logic raise events that carry in their event arguments the photo, canvas details.
Have a collection of objects 'Initiators' that define: 1)an handler that can process Evaluator messages, 2)a simple bool that can be set to indicate if they know what to do with something in the message, and 3)an Action or Process method which can perform or initiate the workflow. Design an interface to abstract these.
Issue the messages. Visit each Initiator, ask it if it can process the lineItem if it can tell it to do so. The processing is kicked off by the 'initiators' and they can call other workflows etc.
Name the pieces outlined above whatever best suits your domain. This should offer some flexibility. Problems may arise depending on concurrent processing requirements and workflow dependencies between the Initiators.
In general, without knowing a lot more detail, size of the project, workflows, use cases etc it is hard to comment.

How to avoid a databinding / events hell on a complex screen?

This is more of an architecture / design question.
I have run into a few projects in the past written in WPF/Windows Forms, etc. that have complex screens with a lot of fields and these fields are connected to each other (their values depend on each other with some logic involved).
These projects I have taken on after they were implemented, and I found a lot of events / data bind hell - what I mean by this is that because all these fields are depending on others they have implemented INotifyPropertyChanged and other fields are being modified as a result. This causes the same fields being updated 5-6 times when the screen loads and the order in which fields are populated causes horrible bugs. (For example, Date was set before Job Type, instead of after Job Type, so I end up with a different Job Fee.)
To make matters worse, some hacks are implemented on UI events (for example, DropDown changed to update field X) while others are in the domain model that the UI binds to.
Basically, it's a huge mess, and I just want to know what the best way to implement something like this is if I was to start from scratch. Or is it a good idea to avoid such a complex screen in the first place?

I would try to keep the business logic out of the property setters as much as possible.
First of all, if several properties are needed for one calculation, I'd write one method that does the calculation, and call that method when appropriate. E.g. if all different combinations of property values make sense, one could just call the method in the setters of each property, making sure that the same code runs any time one of the properties is changed. If you only can evaluate special combinations of property values, you could either implement a command and let the user decide when to calculate the resulting changes, or you could provide feedback through validation, and only evaluate the property changes if the combination is valid. If there are several interdependent properties, I often use a "ChangeInitiator" variable to indicate what property has changed, so that it is clear in the calculation method which property is responsible for the change and which others should change as a result. Basically, this is the same as doing one part of the calculation in each property setter, but I find that it helps me to keep an overview of things if the different parts of the relationship are all in one method.
In a program I wrote once, I had some calculations running on a background thread periodically, so I would just set a flag whenever a piece of data changed that required a new calculation, and do all the updates based on a timer every second or so... that could also help you get the logic more straight, and it avoids to have the calculation run several times for one set of related changes.
With regard to change notification, I'd really try to only use it for UI data binding.

We have fairly complex UIs (including several related fields of different types in, say for example a Row in a DataGrid) and the MVVM pattern has worked pretty well for us. All the properties coming from the Model and exposed to the View that have complex logic related are "wrapped" by an equivalent property in the ViewModel, which has no Backing Field, but rather points directly to the Model:
public class SomeComplexViewModel
{
public SomeModel Model {get;set;}
public string SomeCrazyProperty
{
get
{
return Model.SomeCrazyProperty;
}
{
Model.SomeCrazyProperty = value;
//... Some crazy logic here, potentially modifying some other properties as well.
}
}
}
<TextBox Text="{Binding SomeCrazyProperty}"/>
This removes the "initial value" problem, as the initial value read by the Binding is actually the real value coming from the Model, and thus the logic placed in the Setter is executed only when needed.
Then, for dummy properties (which have no logic behind), we bind directly from the View to the Model:
<TextBox Text="{Binding Model.SomeRegularProperty}"/>
This reduces the bloat in the ViewModel.
With regard to events in the code behind, I totally avoid that. My code behind files are almost always one InitializeComponent() and nothing else.
Only View-Specific logic is placed in the code behind (such as animations stuff, etc), when it cannot be directly done in XAML, or is easier to do in code (which is not the case most of the time).
Edit:
It's important to mention that the winforms binding capabilities are a joke compared to the XAML-based ones. could that be the cause you're seeing those horrible messes in those projects?

mvvm repository filtering

I have some master-detail classes based in large part on Josh Smith's msdn article. Its great code, especially for an example, but leaves me wondering how best to handle situations where you want some subset of a repository.
So Josh has a class called AllCustomersViewModel, and code something like:
public AllCustomersViewModel(CustomerRepository customerRepository)
{
if (customerRepository == null) throw new ArgumentNullException("customerRepository");
// Populate the AllCustomers collection with CustomerViewModels.
_allCustomers = _customerRepository
.GetCustomers()
.Select(cust => new CustomerViewModel(cust, _customerRepository))
.ToList();
}
How do you solve a situation where you want PreferredCustomers, ExCustomers, LocalCustomers, etc, etc??
His code suggests to me a ViewModel class for each, with the filtering of the repository hard-coded in that class.
Or else a way to pass an optional filter into the ViewModel along with the repository?
How does your code solve this particular problem?
As an aside, does anyone have links or good examples showing how to use SpeciaficationPattern or IQueryable to solve issues like this?
Cheers,
Berryl

One option (and probably the cleanest) is to simply add those methods to the CustomerRepository - e.g. GetPreferredCustomers(), GetLocalCustomers() etc.
Also, you should really be working against abstractions, so should pass an ICustomerRepository to your view model constructor. This decouples your view model code from your concrete customer repository (in this case one that reads from an XML file), and makes it easy to swap out implementations, e.g. for unit testing.
The other option, as you mention, is for your repository to expose IQueryable<T>. If you are happy to be tied into IQueryable, and are confident that any data access implementation is going to support a LINQ provider, then that provides good flexibility. See here for more info.
Personally, I prefer the first option, particularly for larger scale applications.

.NET refactoring, DRY. dual inheritance, data access and separation of concerns

Back story:
So I've been stuck on an architecture problem for the past couple of nights on a refactor I've been toying with. Nothing important, but it's been bothering me. It's actually an exercise in DRY, and an attempt to take it to such an extreme as the DAL architecture is completely DRY. It's a completely philosophical/theoretical exercise.
The code is based in part on one of #JohnMacIntyre's refactorings which I recently convinced him to blog about at http://whileicompile.wordpress.com/2010/08/24/my-clean-code-experience-no-1/. I've modified the code slightly, as I tend to, in order to take the code one level further - usually, just to see what extra mileage I can get out of a concept... anyway, my reasons are largely irrelevant.
Part of my data access layer is based on the following architecture:
abstract public class AppCommandBase : IDisposable { }
This contains basic stuff, like creation of a command object and cleanup after the AppCommand is disposed of. All of my command base objects derive from this.
abstract public class ReadCommandBase<T, ResultT> : AppCommandBase
This contains basic stuff that affects all read-commands - specifically in this case, reading data from tables and views. No editing, no updating, no saving.
abstract public class ReadItemCommandBase<T, FilterT> : ReadCommandBase<T, T> { }
This contains some more basic generic stuff - like definition of methods that will be required to read a single item from a table in the database, where the table name, key field name and field list names are defined as required abstract properties (to be defined by the derived class.
public class MyTableReadItemCommand : ReadItemCommandBase<MyTableClass, Int?> { }
This contains specific properties that define my table name, the list of fields from the table or view, the name of the key field, a method to parse the data out of the IDataReader row into my business object and a method that initiates the whole process.
Now, I also have this structure for my ReadList...
abstract public ReadListCommandBase<T> : ReadCommandBase<T, IEnumerable<T>> { }
public class MyTableReadListCommand : ReadListCommandBase<MyTableClass> { }
The difference being that the List classes contain properties that pertain to list generation (i.e. PageStart, PageSize, Sort and returns an IEnumerable) vs. return of a single DataObject (which just requires a filter that identifies a unique record).
Problem:
I'm hating that I've got a bunch of properties in my MyTableReadListCommand class that are identical in my MyTableReadItemCommand class. I've thought about moving them to a helper class, but while that may centralize the member contents in one place, I'll still have identical members in each of the classes, that instead point to the helper class, which I still dislike.
My first thought was dual inheritance would solve this nicely, even though I agree that dual inheritance is usually a code smell - but it would solve this issue very elegantly. So, given that .NET doesn't support dual inheritance, where do I go from here?
Perhaps a different refactor would be more suitable... but I'm having trouble wrapping my head around how to sidestep this problem.
If anyone needs a full code base to see what I'm harping on about, I've got a prototype solution on my DropBox at http://dl.dropbox.com/u/3029830/Prototypes/Prototype%20-%20DAL%20Refactor.zip. The code in question is in the DataAccessLayer project.
P.S. This isn't part of an ongoing active project, it's more a refactor puzzle for my own amusement.
Thanks in advance folks, I appreciate it.

Separate the result processing from the data retrieval. Your inheritance hierarchy is already more than deep enough at ReadCommandBase.
Define an interface IDatabaseResultParser. Implement ItemDatabaseResultParser and ListDatabaseResultParser, both with a constructor parameter of type ReadCommandBase ( and maybe convert that to an interface too ).
When you call IDatabaseResultParser.Value() it executes the command, parses the results and returns a result of type T.
Your commands focus on retrieving the data from the database and returning them as tuples of some description ( actual Tuples or and array of arrays etc etc ), your parser focuses on converting the tuples into objects of whatever type you need. See NHibernates IResultTransformer for an idea of how this can work (and it's probably a better name than IDatabaseResultParser too).
Favor composition over inheritance.
Having looked at the sample I'll go even further...
Throw away AppCommandBase - it adds no value to your inheritance hierarchy as all it does is check that the connection is not null and open and creates a command.
Separate query building from query execution and result parsing - now you can greatly simplify the query execution implementation as it is either a read operation that returns an enumeration of tuples or a write operation that returns the number of rows affected.
Your query builder could all be wrapped up in one class to include paging / sorting / filtering, however it may be easier to build some form of limited structure around these so you can separate paging and sorting and filtering. If I was doing this I wouldn't bother building the queries, I would simply write the sql inside an object that allowed me to pass in some parameters ( effectively stored procedures in c# ).
So now you have IDatabaseQuery / IDatabaseCommand / IResultTransformer and almost no inheritance =)

I think the short answer is that, in a system where multiple inheritance has been outlawed "for your protection", strategy/delegation is the direct substitute. Yes, you still end up with some parallel structure, such as the property for the delegate object. But it is minimized as much as possible within the confines of the language.
But lets step back from the simple answer and take a wide view....
Another big alternative is to refactor the larger design structure such that you inherently avoid this situation where a given class consists of the composite of behaviors of multiple "sibling" or "cousin" classes above it in the inheritance tree. To put it more concisely, refactor to an inheritance chain rather than an inheritance tree. This is easier said than done. It usually requires abstracting very different pieces of functionality.
The challenge you'll have in taking this tack that I'm recommending is that you've already made a concession in your design: You're optimizing for different SQL in the "item" and "list" cases. Preserving this as is will get in your way no matter what, because you've given them equal billing, so they must by necessity be siblings. So I would say that your first step in trying to get out of this "local maximum" of design elegance would be to roll back that optimization and treat the single item as what it truly is: a special case of a list, with just one element. You can always try to re-introduce an optimization for single items again later. But wait till you've addressed the elegance issue that is vexing you at the moment.
But you have to acknowledge that any optimization for anything other than the elegance of your C# code is going to put a roadblock in the way of design elegance for the C# code. This trade-off, just like the "memory-space" conjugate of algorithm design, is fundamental to the very nature of programming.

As is mentioned by Kirk, this is the delegation pattern. When I do this, I usually construct an interface that is implemented by the delegator and the delegated class. This reduces the perceived code smell, at least for me.

I think the simple answer is... Since .NET doesn't support Multiple Inheritence, there is always going to be some repetition when creating objects of a similar type. .NET simply does not give you the tools to re-use some classes in a way that would facilitate perfect DRY.
The not-so-simple answer is that you could use code generation tools, instrumentation, code dom, and other techniques to inject the objects you want into the classes you want. It still creates duplication in memory, but it would simplify the source code (at the cost of added complexity in your code injection framework).
This may seem unsatisfying like the other solutions, however if you think about it, that's really what languages that support MI are doing behind the scenes, hooking up delegation systems that you can't see in source code.
The question comes down to, how much effort are you willing to put into making your source code simple. Think about that, it's rather profound.

I haven't looked deeply at your scenario, but I have some thoughs on the dual-hierarchy problem in C#. To share code in a dual-hierarchy, we need a different construct in the language: either a mixin, a trait (pdf) (C# research -pdf) or a role (as in perl 6). C# makes it very easy to share code with inheritance (which is not the right operator for code-reuse), and very laborious to share code via composition (you know, you have to write all that delegation code by hand).
There are ways to get a kind of mixin in C#, but it's not ideal.
The Oxygene (download) language (an Object Pascal for .NET) also has an interesting feature for interface delegation that can be used to create all that delegating code for you.

What is a real-life use for the builder design pattern?

I've read about it, I understand it's basic function--I'd like to know an example of a common, real-life use for this pattern.
For reference, I work mostly with business applications, web and windows, using the Microsoft stack.

Think of an Itinerary builder. There are lots of things you can add to you Itinerary like hotels, rental cars, airline flights and the cardinality of each is 0 to *. Alice might have a car and hotel while Bob might have two flights, no car and three hotels.
It would be very hard to create an concrete factory or even an abstract factory to spit out an Itinerary. What you need is a factory where you can have different steps, certain steps happen, others don't and generally produce very different types of objects as a result of the creation process.
In general, you should start with factory and go to builder only if you need higher grain control over the process.
Also, there is a good description, code examples and UML at Data & Object Factory.

Key use cases:
When the end result is immutable, but
doing it all with a constructor would
be too complicated
When I want to partially build
something and reuse that partially
built thing, but customize it at
the end each time
When you start with the factory pattern, but the thing being built by
the factory has too many permutations
In summary, builder keeps your constructors simple, yet permits immutability.
You said C#, but here's a trivial Java example:
StringBuilder sb = new StringBuilder();
sb.append("Hello");
sb.append(" ");
sb.append("World!");
System.out.println(sb.toString());
As opposed to:
String msg = "";
msg += "Hello";
msg += " ";
msg += "World!";
System.out.println(msg);

EDIT: You will see in my comments that I may have rushed into answering this question, and confused myself in the process. I will go ahead and edit this to work with the Abstract Factory, as I think I originally intended, but please note that this is mainly for reference, not necessarily as a response to the original question.
The most common example I've seen described deals with how GUI components are built.
For example, if you were designing a form for your application, whose GUI components could take on multiple representations (perhaps based on which platform you were running on), you would design an abstract factory to handle the creation of those components.
In order to add new controls to the form, the code might look something like this:
public MyForm ()
{
GuiFactory factory = new Win32Factory ();
Button btn = factory.CreateButton ();
btn.Text = "Go!"
btn.Location = new Point (15, 50);
this.Controls.Add (btn);
}
This satisfies the Abstract Factory pattern because you can create different instances of the factory object to create different representations of your created objects without changing the client code (this is a rudimentary example, but I think normally you wouldn't create the Win32Factory using new, it would be acquired via some other abstraction).

A common example that we used to see all the time was a "sysgen" of an operating system. you had a process that selected all the modules you needed, configured them, and returned a bootable image that had been customized.

One use case that I've encountered is when having multiple data sources. The particular case involved a cache and a database. The majority of the data was pulled from cache, or not. The second loader looked at the data to see whether or not it was loaded from the cache. It would query the database to finish populating the data.

Sometimes it can be helpful to think of non-software related example of design patterns in order to understand them.
I have a system I am working on now that uses a builder to create an order. The order is a class composed of several other classes. My builder creates and validates the associated classes, and if all are valid it then creates an instance of the order class. This way I can be sure that I never have an instance of an order that is missing data.