tsJensen

A quest for software excellence...

Custom Recursive Model Validation in .NET Using Data Annotations

Need to write your own model validator outside the scope of an application framework such as ASP.NET MVC? A short while ago, I needed to do just that. I was writing a WCF service with a relatively complex data model which required a much greater level of validation than the DataMember attribute’s IsRequired property could provide.

Here’s the solution I found. But first a bit of background.

Validation in ASP.NET MVC 
I’ve been using Data Annotations attributes for view model validation for years in the context of ASP.NET MVC for model validations, client and server side. I always took the server side validation for granted and looked at the client side with greater interest. When getting started with ASP.NET MVC, I used Steve Sanderson’s xVal library. Then I switched to ASP.NET MVC 3’s client side validation.

For client side validation, I’m really starting to like jQuery’s unobtrusive validation and the ASP.NET MVC’s HtmlHelper class and its GetUnobtrusiveValidationAttributes method. And for the server side, view model binding and the ModelState.IsValid property works fine.

Validation Without an App Framework 
But this post is not about client side validation or server side validation in ASP.NET MVC. I had to do the validation against the model in the WCF service which, as far as I know, does not have a nice model validation facility other than its own data model serialization which just throws a nasty exception should the data being passed over the wire not provide required data.

So why not use the same approach used by our friends in the ASP.NET MVC world. A little Google investigation turned up something that looked like exactly what I wanted. I found an answer posted to StackOverflow by Mike Reust which included a link to his DataAnnotationsValidatorRecursive library. (Gotta love StackOverflow.)

After some experimentation, I had made some tweaks to Mike’s code and came up with something that worked the way I wanted it to. Here’s a partial example of a data model and how the ValidateObject with it’s optional MinOccursOnEnumerable can be used to require one or more items to be included in a required complex enumerable type that will get recursively.

[DataMember(IsRequired = true), 
	Required(ErrorMessage = "Employer cannot be null."), 
	ValidateObject]
public Employer Employer { get; set; }


[DataMember(IsRequired = true), 
	Required(ErrorMessage = "Children cannot be null."), 
	ValidateObject(MinOccursOnEnumerable = 1)]
public Child[] Children { get; set; }

Using the recursive validation library is easy. Here’s an example:

//perform validation using DataAnnotations for custom validation messages
List<ValidationResult> results = new List<ValidationResult>();
bool isValid = DataAnnotationsValidator.TryValidateObjectRecursive<MyModelData>(model, results);

//now examine isValid and the results

And here’s the code for the validation extensions and ValidateObject attribute.

using System.Collections;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System;

namespace MyValidator
{
	public static class DataAnnotationsValidator
	{
		public static bool TryValidateObject(object obj, ICollection<ValidationResult> results)
		{
			return Validator.TryValidateObject(obj, new ValidationContext(obj, null, null), results, true);
		}

		public static bool TryValidateObjectRecursive<T>(T obj, List<ValidationResult> results)
		{
			bool result = TryValidateObject(obj, results);

			var properties = obj.GetType().GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(ValidateObjectAttribute)));

			foreach (var property in properties)
			{
				var valAttrib = property.GetCustomAttributes(typeof(ValidateObjectAttribute), true).FirstOrDefault() as ValidateObjectAttribute;
				var value = obj.GetPropertyValue(property.Name);

				if (value == null || valAttrib == null) continue;

				var asEnumerable = value as IEnumerable;
				if (asEnumerable != null)
				{
					List<object> items = new List<object>();
					foreach (var enumObj in asEnumerable) items.Add(enumObj);
					foreach (var enumObj in items)
					{
						result = TryValidateObjectRecursive(enumObj, results) && result;
					}
					if (items.Count < valAttrib.MinOccursOnEnumerable)
					{
						string errorMessage = valAttrib.ErrorMessage ?? "MinOccursOnEnumerable validation failed.";
						results.Add(new ValidationResult(errorMessage));
						result = false;
					}
				}
				else
				{
					result = TryValidateObjectRecursive(value, results) && result;
				}
			}

			return result;
		}
	}

	public static class ObjectExtensions
	{
		public static object GetPropertyValue(this object o, string propertyName)
		{
			object objValue = string.Empty;

			var propertyInfo = o.GetType().GetProperty(propertyName);
			if (propertyInfo != null)
			{
				objValue = propertyInfo.GetValue(o, null);
			}
			return objValue;
		}
	}
}

You need to use the ValidateObject attribute on any complex type you want validated deeply. I found out the hard way that if you try to validate all reference objects, you get nasty results on DateTime properties.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace MyValidator
{
	[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, Inherited = false, AllowMultiple = false)]
	public class ValidateObjectAttribute : Attribute
	{
		int _minOccurs = 0;
		//marker for object properties that need to be recursively validated

		public ValidateObjectAttribute() { }

		public int MinOccursOnEnumerable { get { return _minOccurs; } set { _minOccurs = value; } }

		public string ErrorMessage { get; set; }
	}
}

Of course you can take off on this or Mike’s original code and create your own validation library for a WCF service, a business logic layer, or whatever you need. Good luck and please update me on your validation adventures.

Where Agile Succeeds

In the interests of keeping the U.S. Postal Service in business, I subscribe to a number free technology periodicals. I’m too cheap to pay for anything more than MSDN Magazine. One of the free rags I like to keep in the reading room is Information Week.

A recent article entitled Where Agile Fails caught my eye. You can get a copy of it online if you want to hand over your contact info. I enjoyed the article and it makes a good general point. The author Charles Babcock draws our attention to the fact that many agile teams overlook operations and the challenges brought about by frequent releases into production.

I was only disappointed in the title. Any reader who quickly browses the article, allowing the title to influence conclusions, may walk away with the wrong idea. The title would be more informative if less typographically attractive as Where Agile Teams Fail to Involve Operations, Agile Teams Fail.

When agile development is done right, it includes as part of release and sprint planning some elements of deployment, operations, support and maintenance. Some sprints or releases planned may not go into production, so operations need not be involved too heavily, but I think they should be be apprised of the team’s plans and progress and given the opportunity to prepare in advance for the needs of the application and users.

When a release or sprint will go into production, the operations team should be represented in the planning meetings. This will give them the opportunity to learn what is expected of them and plan accordingly. It will also give them a chance to ask questions, raise concerns or even point out why they will not be able to support a go-live date for a release. And when that is the case, you want to know sooner rather than later.

Where agile succeeds is in the notion that people and interactions are more important than processes. The Manifesto does not indicate that it is referring only to developers. Clearly that is not the case. Operations people are people too. Yes, Fred, they really are.

Agile Software Design, Architecture and Planning Tools

Dr. Dobbs published the Jolt Awards for Design, Architecture and Planning Tools today. The Jolt judges make a very important introductory point before discussing the specific winners.

“On large projects, it can be difficult to state requirements, do the design work, and still maintain Agile's orientation towards accepting — even welcoming — new changes from users.

“Those issues notwithstanding, I've noticed that most large or mid-sized projects with mission-critical implications invariably do indeed gather requirements carefully and design the product accordingly. Agile, if it's in use in the organization, typically is most evident in the coding and testing stages.

“Tools that can capture requirements, help illustrate and validate design, and plan the implementation are still very much needed.“

One of the greatest misunderstandings of Agile software development is the assumption that if one thing is valued over another, the thing with lesser value has no value. Let us review the manifesto:

Manifesto for Agile Software Development

We are uncovering better ways of developing
software by doing it and helping others do it.
Through this work we have come to value:

Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan

That is, while there is value in the items on
the right
, we value the items on the left more.

I have added my own emphasis to highlight the point that is so often overlooked by Agile critics and enthusiasts alike. The critic decries Agile for eliminating design, architecture and planning, and yet Agile does nothing of the sort. The enthusiast rushes to write code thinking that Agile is a magic bridge over the need to endure the tedium of design, architecture and planning, and yet, nothing could be further from the truth.

After all, how can you set out to intelligently implement a use case if you do not first fully understand the design and architecture that supports the use case? And how will you know that you are implementing that use case at the right time without proper planning?

As the Jolt judges point out, the design, architecture and planning tools we choose to use in an Agile development shop “must be less heavy than in years past and more easily configured to fit the needs of the organization, rather than implementing a specific methodology to which the organization must migrate its orientation, if not its processes.”

I’m excited to check out the winners the judges have chosen. Visit the link at the beginning of this post and check them out yourself.

Whatever tools you choose for doing your design, architecture and planning, do not make the mistake of thinking that these critical phases of development are eliminated by Agile. You may go about these phases with a new attitude toward what is important and with a more realistic view of the realities of the evolution of a product during all phases of development, but you will not ignore them without significant risk. In fact, I think they need to be embraced by Agile teams remaining focused on the use cases and not the frameworks.

C# Basics: On the Importance of the Using Statement and IDisposable

The world of .NET programming is full of objects that implement the IDisposable interface. File, Font, DataContext, Stream, DbConnection, and many more—all implement the IDisposable interface. And for good reason. They touch the outside world and the outside world is messy, full of resource allocations that can only be used one at a time and must be explicitly returned to their owner to be used by another caller.

So in this 8th installment of C# Basics, let’s take a look at how best to use the IDisposable interface by simply using the using statement. The using statement is really just syntactic sugar but it helps you produce much more readable and reliable code.

using (var myobj = new MyDisposable())
{
  myobj.DoSomething();
}

You can even stack them like this:

using (var myobj = new MyDisposable())
using (var otherobj = new MyOtherDisposable())
{
  var x = myobj.DoSomething();
  otherobj.DoAnotherThing(x);
}

Of course, you could write your own resource cleanup explicitly, but it can start to look a bit messy and as lazy as we often are, the cleanup often gets forgotten.

var myobj = new MyDisposable();
var otherobj = new MyOtherDisposable();
try
{
  var x = myobj.DoSomething();
  otherobj.DoAnotherThing(x);
}
finally
{
  if (otherobj != null) otherobj.Dispose();
  if (myobj != null) myobj.Dispose();
}

Use the using statement where you can. It's not a one size fits all syntax sugar, but it is sweet where it fits.

Dennis Ritchie, RIP, Thanks for C

Dennis Ritchie, the Father of C, passed away a few days ago. A friend asked me today, “Would we have had a Steve Jobs without first having a Dennis Ritchie?” He made a great point. The most common programming language for the Apple platform today is Objective-C. Mr. Ritchie was not an attention hound it seems. I doubt more than 1% of the people who know who Steve Jobs is would know who Dennis Ritchie is, and yet, we in this business of programming owe him a great debt of gratitude.

I know there are C detractors, but the ubiquity of C and all it’s descendants cannot be denied. Andrew Binstock, in his column today on Dr. Dobbs, quoted Mr. Ritchie as having said:

“C is quirky, flawed, and an enormous success. [And UNIX] is very simple, it just needs a genius to understand its simplicity.” ~Dennis Ritchie

Oh yeah, and I forgot to mention he was also deeply involved in developing UNIX. And how many derivatives of UNIX are there? And how many other operating systems at their core are so like UNIX as to make the grand old operating system the true grandfather or at least uncle of every seriously utilized operating system in the world?

I will end by borrowing Mr. Binstock’s conclusion:

“Ritchie saw in language what others could not see, in operating system what others had not built, and in the world around him what others did not realize. His insight and the elegance of his work will be missed by all programmers, even in future generations who, as he would want it, might know nothing of him.” ~Andrew Binstock

Thanks, Dennis Ritchie. Thanks for C. And thanks for UNIX.

And whatever you do, don’t miss this farewell from MuppetLabs. Thanks for sharing it, Dave.

C# 5.0 Exciting New Asynchrony Features Coming

I’m gradually catching up with presentations from last month’s BUILD conference on Channel 9. Today I ran into a blog post by Samuel Jack in the UK on the topic of what’s new in C# 5.0. I recommend you read his blog, but more strongly recommend you watch Anders Hejlberg’s presentation on Channel 9 about C# 5.0 and VB 11.0.

Among my favorite goodies are the async and await keywords. For anyone who has put off learning how to write asynchronous application behavior because it is just too hard to understand, you are in luck. Wait a few more months, perhaps a year, and you can learn just a few easy concepts about how to use async and await keywords in your code and you will be an asynchronous coding wizard.

Exciting times!

C# Basics: const vs readonly vs static

In this 7th installment of C# Basics, I’m going to cover the differences between the modifiers const, readonly, and static, specifically in reference to class members where the developer wishes to use the fields or properties in client code that cannot change the value of that member.

To illustrate and discuss the differences between each modifier, I’ve put together a contrived set of classes with the least amount of code I can think to add in order to review and to examine the differences in the IL (intermediate language) taken from Ildasm.exe. (Visit this nice page to learn how to use Ildasm.exe from with Visual Studio.)

using System;

namespace ReadOnlyConstant
{
  public class MyConstOnly
  {
    // assigned at declaration and used at compile time only
    public const int Age = 20;
  }

  public class MyReadOnly
  {
    // can only be assigned in declaration or constructor
    public readonly int Age = 0;
    public MyReadOnly()
    {
      Age = 20;
    }
  }

  public static class MyStaticOnly
  {
    // can be assigned within class but "readonly" for client
    private static int _age = 20;
    public static int Age { get { return _age; } }
  }
}

The goal in each class above is to create a public field or member that can be read by client code but cannot be changed by client code. Looking through the IL produced by compiling this code can also be instructive even if you do not fully understand each and every IL instruction. Take a look here at these classes under the compiled covers and notice that the MyConstOnly class does not have a getter method to retrieve Age nor is it's value set in the .ctor but only noted by the compiler in the .field definition for use by the compiler later should client code use it. Then read through to the client code and see its IL code as well.

// =============== CLASS MEMBERS DECLARATION ===================

.class public auto ansi beforefieldinit ReadOnlyConstant.MyConstOnly
       extends [mscorlib]System.Object
{
  .field public static literal int32 Age = int32(0x00000014)
  .method public hidebysig specialname rtspecialname 
          instance void  .ctor() cil managed
  {
    // Code size       7 (0x7)
    .maxstack  8
    IL_0000:  ldarg.0
    IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
    IL_0006:  ret
  } // end of method MyConstOnly::.ctor

} // end of class ReadOnlyConstant.MyConstOnly

.class public auto ansi beforefieldinit ReadOnlyConstant.MyReadOnly
       extends [mscorlib]System.Object
{
  .field public initonly int32 Age
  .method public hidebysig specialname rtspecialname 
          instance void  .ctor() cil managed
  {
    // Code size       25 (0x19)
    .maxstack  8
    IL_0000:  ldarg.0
    IL_0001:  ldc.i4.0
    IL_0002:  stfld      int32 ReadOnlyConstant.MyReadOnly::Age
    IL_0007:  ldarg.0
    IL_0008:  call       instance void [mscorlib]System.Object::.ctor()
    IL_000d:  nop
    IL_000e:  nop
    IL_000f:  ldarg.0
    IL_0010:  ldc.i4.s   20
    IL_0012:  stfld      int32 ReadOnlyConstant.MyReadOnly::Age
    IL_0017:  nop
    IL_0018:  ret
  } // end of method MyReadOnly::.ctor

} // end of class ReadOnlyConstant.MyReadOnly

.class public abstract auto ansi sealed beforefieldinit ReadOnlyConstant.MyStaticOnly
       extends [mscorlib]System.Object
{
  .field private static int32 _age
  .method public hidebysig specialname static 
          int32  get_Age() cil managed
  {
    // Code size       11 (0xb)
    .maxstack  1
    .locals init ([0] int32 CS$1$0000)
    IL_0000:  nop
    IL_0001:  ldsfld     int32 ReadOnlyConstant.MyStaticOnly::_age
    IL_0006:  stloc.0
    IL_0007:  br.s       IL_0009

    IL_0009:  ldloc.0
    IL_000a:  ret
  } // end of method MyStaticOnly::get_Age

  .method private hidebysig specialname rtspecialname static 
          void  .cctor() cil managed
  {
    // Code size       8 (0x8)
    .maxstack  8
    IL_0000:  ldc.i4.s   20
    IL_0002:  stsfld     int32 ReadOnlyConstant.MyStaticOnly::_age
    IL_0007:  ret
  } // end of method MyStaticOnly::.cctor

  .property int32 Age()
  {
    .get int32 ReadOnlyConstant.MyStaticOnly::get_Age()
  } // end of property MyStaticOnly::Age
} // end of class ReadOnlyConstant.MyStaticOnly

// =============================================================

You can read the MSDN full explanations of each modifier but here’s the basics:

const
Can only be assigned a value in declaration and can only be a value type or string. Use the const modifier when you KNOW the value won’t change. If you think it might change at a later date and your assembly is distributed as a compiled library, consider one of the other modifiers to assure that you don’t have a value you didn’t expect in your client code. (See use code sample below.)

readonly
Can assign a value at declaration or in the class constructor. It is important to note that if you use a reference type with modifiable members, your client code can still modify those members even if it cannot assign a value to the readonly reference. Note in the IL above that the initialization of the declared value occurs in the .ctor before the assignment in the .ctor, so if you are wondering which would be better, now you have some insight into that question.

static
Can assign the value of the private member anywhere within the class code. Note the initialization of the value in the static .ctor of the class. You could also assign the value in some other method later but with the public property implementing only a get, the client code cannot assign a value.

And here is the client code and it’s IL just below it. The most important point to note in the IL is that the client code is compiled with the const’s literal value, NOT a get to the class. This is why you must watch for the use of a const that could change with a new library. Make sure you compile your client code against that new library when you get it or you could be very sorry when the library is using one const compiled value and you’re using another.

namespace TestConsole
{
  class Program
  {
    static void Main(string[] args)
    {
      // compiler will replace with constant value
      // If the referenced assembly is changed to 40 and this is
      // not compiled again against that new assembly, the value
      // for mcoAge will still be 20. (See IL below.)
      int mcoAge = MyConstOnly.Age;

      MyReadOnly mro = new MyReadOnly();
      int mroAge = mro.Age;

      int msoAge = MyStaticOnly.Age;

      Console.WriteLine("{0} {1} {2}", mcoAge, mroAge, msoAge);
    }
  }
}

// output: 20 20 20

// and here is the IL with some of my own comments

// =============== CLASS MEMBERS DECLARATION ===================

.class private auto ansi beforefieldinit TestConsole.Program
       extends [mscorlib]System.Object
{
  .method private hidebysig static void  Main(string[] args) cil managed
  {
    .entrypoint
    // Code size       53 (0x35)
    .maxstack  4
    .locals init ([0] int32 mcoAge,
             [1] class [ReadOnlyConstant]ReadOnlyConstant.MyReadOnly mro,
             [2] int32 mroAge,
             [3] int32 msoAge)
    IL_0000:  nop
    IL_0001:  ldc.i4.s   20   //NOTE: literal value assigned - no mention of MyConstOnly class
    IL_0003:  stloc.0
    IL_0004:  newobj     instance void [ReadOnlyConstant]ReadOnlyConstant.MyReadOnly::.ctor()
    IL_0009:  stloc.1
    IL_000a:  ldloc.1
    IL_000b:  ldfld      int32 [ReadOnlyConstant]ReadOnlyConstant.MyReadOnly::Age
    IL_0010:  stloc.2
    IL_0011:  call       int32 [ReadOnlyConstant]ReadOnlyConstant.MyStaticOnly::get_Age()
    IL_0016:  stloc.3
    IL_0017:  ldstr      "{0} {1} {2}"
    IL_001c:  ldloc.0
    IL_001d:  box        [mscorlib]System.Int32
    IL_0022:  ldloc.2
    IL_0023:  box        [mscorlib]System.Int32
    IL_0028:  ldloc.3
    IL_0029:  box        [mscorlib]System.Int32
    IL_002e:  call       void [mscorlib]System.Console::WriteLine(string,
                                                                  object,
                                                                  object,
                                                                  object)
    IL_0033:  nop
    IL_0034:  ret
  } // end of method Program::Main

  .method public hidebysig specialname rtspecialname 
          instance void  .ctor() cil managed
  {
    // Code size       7 (0x7)
    .maxstack  8
    IL_0000:  ldarg.0
    IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
    IL_0006:  ret
  } // end of method Program::.ctor

} // end of class TestConsole.Program

// =============================================================

Meaningless Meetings Meander Morosely Mostly

Recently I came across an interesting list of top ten time wasters at work. I jotted them down but have lost the source, so I apologize for not providing the link. Here’s their list:

  1. Instant Messaging
  2. Over-Reliance on Email
  3. Meandering Meetings
  4. Short Gaps Between Meetings
  5. Reacting to Interruptions
  6. Ineffective Multi-Tasking
  7. Disorganized Workspace
  8. Personal Communication
  9. Web Surfing "Breaks"
  10. Cigarette/Coffee Breaks

It’s a decent list that one might find on many top ten sites, I’m sure. But it’s not terribly accurate. You see, the biggest time waster in the enterprise is the Meaningless, Meandering Meeting Machine. So here’s my revised list:

  1. Thinking about meetings.
  2. Planning meetings.
  3. Doodling in meetings.
  4. Talking about meetings.
  5. Scheduling and rescheduling meetings.
  6. Meetings.
  7. Follow-up meetings.
  8. Looking or asking for minutes from meetings.
  9. Assuming people will do what was agreed to in meetings.
  10. Making lists about meetings.

I have seen good, productive employees become consumed by the Meaningless Meetings Machine. It is an endless recursive function leading to enterprise stack overflow. Sometimes executives are lost for months in the Machine and when employees smart enough or lucky enough to stay away from the Machine are asked if they have seen Mr. Soandso, they say, No, and hurriedly move on lest they too be sucked into the Machine.