2008-03-11 - On Holiday

So just a short note to say that I got married on the 23rd of Feb
to the love of my life Renee... a good time was had by all, even
though the weather was horrific (rained
non-stop for 2 days) - big thanks to Ben, Nick, Stu, Sacha (my
Entourage) and everyone else for helping with the last minute
re-organisations :)

I'm now on honeymoon in Europe... currently lurking in Rome for a
few days to take in the local sights - however we'll be making our
way to England soon to catch up with some family.

For anyone curious about the Architecture Chat, it'll start up
again in April once I'm back in New Zealand and my life has
returned to some semblance of normality.

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Leveraging Member Initializers

So a few weeks back there was a  post on the Genome TeamBlog which included a link to one of my  lambda abuse posts from last year.

At any rate - the problem they faced was that with code like this:

DataContext Context = new DataContext();

string connStr = "";

DataDomainSchema schema = DataDomainSchema.LoadFrom("SomeMappingFile");

schema.CreateDbSchema(connStr);

DataDomain dd = new DataDomain(schema, connStr);

using (Context.Push(ShortRunningTransactionContext.Create()))
{
Customer tt = dd.New();
tt.Name = "TechTalk";

RootProject tt_hk = dd.New();
tt_hk.Name = "Housekeeping";

ChildProject tt_hk_hol = dd.New();
tt_hk_hol.Name = "Holiday";
tt_hk.ChildProjects.Add(tt_hk_hol);

ChildProject tt_hk_ill = dd.New();
tt_hk_ill.Name = "Illness";

tt_hk.ChildProjects.Add(tt_hk_ill);

tt.RootProjects.Add(tt_hk);

RootProject tt_g = dd.New();
tt_g.Name = "Genome";

ChildProject tt_g_dev = dd.New();
tt_g_dev.Name = "Development";
tt_g.ChildProjects.Add(tt_g_dev);

ChildProject tt_g_mnt = dd.New();
tt_g_mnt.Name = "Maintenance";
tt_g.ChildProjects.Add(tt_g_mnt);
tt.RootProjects.Add(tt_g);

Context.CommitCurrent();
}


You ended up with a very flat member initialization structure plagued with:
  • Having to explicitly name child instances being added to collections - there's a lot of unnecessary noise.
  • Where you can't easily see the structure i.e. it's not visually hierarchical, so at a glance you're not sure just what the structure is compared to say looking at an xml document with nested elements where it's quite obvious.


At any rate, the guys at the Genome project attempted to overcome this using the nested lambdas (what I coined a "DSL" at the time, though It's a terrible and inaccurate term for what's effectively just a bit of a "trick" relying on side effects of evaluation) - it didn't go so well though because of course at first glance the syntax look strongly typed, the reality is it's anything but, and refactoring tools just aren't going to do things like renaming of keys in the hash style syntax i.e. key => value, because the key is just a Lambda parameter.

But all is not lost - of course with C# 3.0 we already have a great syntax for doing this kind of hierarchical initialization, say for this set of types:

public class BlogPost
{
private readonly List _tags = new List();
private readonly BlogUser _createdBy = new BlogUser();

public string Title { get; set; }

public string Body { get; set; }

public List Tags
{
get { return _tags; }
}

public BlogUser CreatedBy
{
get { return _createdBy; }
}

public BlogUser LastEditedBy { get; set; }
}

public class BlogUser
{
public int Age { get; set; }
public string Name { get; set; }
}


We could do something like this to initialize an instance of BlogPost:
BlogPost post = new BlogPost()
{
Title = "Post on Lambdas",
Body = "This is a post...",
Tags =
{
".Net",
"Lambda",
"C#3.0"
},
CreatedBy =
{
Name = "Jane Doe",
Age = 35
},
LastEditedBy = new BlogUser()
{
Name = "Joe Bloggs",
Age = 25
}
};

But the catch for the Genome guys is that it looks like they need to construct their entities using their DataDomain class ...  I don't know about how there product works but I can only assume it's either to get a transparent proxy for change tracking purposes or to enlist it into the current session etc. (though if it's just to enlist the entity I can't see why they need to bother with getting the DataDomain to create a new instance, surely they could manually enlist it).

At any rate that's irrelevant :)

So I got to thinking that of course member initialization is one of the Lambda-friendly things we can do because it's expressed in a single statement - so we can happily take the above code snippet and express it like so:

BlogPost post = evaluator.Create(() => new BlogPost()
{
Title = "Post on Lambdas",
Body = "This is a post...",
Tags =
{
".Net",
"Lambda",
"C#3.0"
},
CreatedBy =
{
Name = "Jane Doe",
Age = 35
},
LastEditedBy = new BlogUser()
{
Name = "Joe Bloggs",
Age = 25
}
});

Where evaluator is an instance of a class I wrote called ServiceInjectionEvaluator ... the Create method (as you can probably guess) has the following signature:
public T Create(Expression<>> expression)

The service injection evaluator just relies on being configured with an  IServiceProvider capable of resolving instances of types... at this point we just unwind the expression, substituting our own instance activation mechanism wherever we stumble upon a  NewExpression and walking through the expressions executing each bit as required - though it makes the assumption that you're going to have either a New or MemberInit expression at the top level of the Lambda, otherwise we just compile the whole thing and throw it back without any changes (because I don't want to bother writing code to visit the other types of expression node).
public class ServiceInjectionEvaluator
{
private readonly IServiceProvider _serviceProvider;

public ServiceInjectionEvaluator(IServiceProvider serviceProvider)
{
_serviceProvider = serviceProvider;
}

public T Create(Expression<>> expression)
{
switch (expression.Body.NodeType)
{
case ExpressionType.New:
case ExpressionType.MemberInit:
return (T)EvaluateExpression(expression.Body);
default:
return expression.Compile().Invoke();
}
}

private object GetInstanceWithInit(MemberInitExpression expression)
{
object instance = GetInstance(expression.NewExpression);
foreach (MemberBinding binding in expression.Bindings)
{
ApplyBinding(instance, binding);
}
return instance;
}

private void ApplyBinding(object instance, MemberBinding binding)
{
switch (binding.BindingType)
{
case MemberBindingType.Assignment:
ApplyAssignmentBinding(instance, (MemberAssignment)binding);
break;
case MemberBindingType.ListBinding:
ApplyListBinding(instance, (MemberListBinding)binding);
break;
case MemberBindingType.MemberBinding:
ApplyMemberBinding(instance, (MemberMemberBinding)binding);
break;
default:
throw new NotImplementedException();
}
}

private void ApplyMemberBinding(object instance, MemberMemberBinding binding)
{
PropertyInfo property = (PropertyInfo)binding.Member;
object memberValue = property.GetValue(instance, null);
foreach (MemberBinding childBinding in binding.Bindings)
{
ApplyBinding(memberValue, childBinding);
}
}

private void ApplyListBinding(object instance, MemberListBinding binding)
{
object list = ((PropertyInfo)binding.Member).GetValue(instance, null);

foreach (ElementInit elementInit in binding.Initializers)
{
Delegate compiled = Expression.Lambda(Expression.NewArrayInit(typeof(object), elementInit.Arguments.ToArray())).Compile();
object[] arguments = (object[])compiled.DynamicInvoke();
elementInit.AddMethod.Invoke(list, arguments);
}
}

private void ApplyAssignmentBinding(object instance, MemberAssignment assignment)
{
object value = EvaluateExpression(assignment.Expression);
PropertyInfo info = (PropertyInfo)assignment.Member;
info.SetValue(instance, value, null);
}

private object EvaluateExpression(Expression expression)
{
switch (expression.NodeType)
{
case ExpressionType.New:
return GetInstance((NewExpression) expression);
case ExpressionType.MemberInit:
return GetInstanceWithInit((MemberInitExpression) expression);
default:
return Expression.Lambda(expression).Compile().DynamicInvoke();
}
}

private object GetInstance(NewExpression expression)
{
return _serviceProvider.GetService(expression.Type);
}
}


The only thing left is to then either provide an existing instance of IServiceProvider (i.e. the Windsor container) or creating an adaptor
public class DataDomainServiceProvider : IServiceProvider
{
private readonly DataDomain _domain;
private static readonly MethodInfo member = typeof(DataDomain).GetMethod("New");

public DataDomainServiceProvider(DataDomain domain)
{
_domain = domain;
}

public object GetService(Type serviceType)
{
return member.MakeGenericMethod(serviceType).Invoke(_domain, null);
}
}


There's a few things the enterprising mind can do with substitutions and member initialization I can think of, especially around IoC - anyone else have some ideas or thoughts on using/abusing them?
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SharePoint Peeves

I have to say SharePoint just continues to underwhelm me (as a developer, I don't mind the product itself I should probably make that clear)...

A couple of quick examples:

Configuration over Convention


Regional settings and dates are a prime example - for instance you get a which brings with it a common look and feel for date pickers in SharePoint... and on the various pre-canned forms etc. everything appears to display with the current user/sites regional settings.

However whenever you use this control you end up resorting to code along the lines of:

SPRegionalSettings regionalSettings = SPContext.Current.Web.CurrentUser.RegionalSettings ?? SPContext.Current.Web.RegionalSettings; myDatePickerControl.LocaleId = (int)regionalSettings.LocaleId;

Or extending your control yourself to do the same... why on earth would I not want the control to default to the current regional settings?

Again the lack of convention rears it's ugly head when working with SharePoint's SPGridView - if it's going to a render a date, why doesn't it render it with the current user's Locale in mind (which I've talked about in this  hack last year) - shouldn't these controls be taking that burden of responsibility away from me?

Useless Extensions Points


When something is extensible in SharePoint, then generally:
  1. It's not documented (except by the community)
  2. It doesn't really work for the most common scenario.


Take the  SPGridView and  SPDataSource combo - with this you can setup a grid to feed
from a CAML query pretty easily ... and it's smart enough to add the required to the underlying CAML query when you sort on a column... so far so good.

But what if you want to sort on more then one column?

Well, you could try specifying more then one column in the grid's SortExpression - but this causes the SPDataSource to spit the dummy... so obviously the first question is why doesn't that work, when it works for other data sources, and would have been trivial
to implement.

But not all hope is lost after opening reflector and perusing the code (which thankfully wasn't obfuscated in this case, though quite a bit of it is) you see that in fact you can specify additional sort columns in the original query and the SPDataSource is smart enough to keep them and insert the new field references into the existing ... a handy way for extending your query to have a number of default sort columns.

But there's a catch, it sticks the entries in the wrong position, so it will sort by the fixed columns first - rather then last - making it all but useless in most cases (users expect to click on a column and see the results sorted by the selected column first) .. And to be honest this still wouldn't worry me if I was given at least one virtual method to override allowing me to mutate the CAML query appropriately.

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Architecture Chat 24 Next Week

Hi all...  So first off, there's no Architecture Chat today - I'm tied up with prior commitments (due to the short week) so it's going to be held Thursday next week -14th of February, apologies to anyone who was going to attend.

As far as possible topics, what about:

  • All the interesting stuff that came out of Lang.Net (or at least was brought to my attention by that symposium)
  • Cosmos - a cute operating system written in C#.
  • Charlie Calvert's started posting on the future of C# (4.0).
  • Jumbala - another interesting step down the MDA road, this time as an
    action language for UML state machines... which can actually be compiled.
  • .Net Mass Downloader - here's something I was thinking of doing myself, a mass download for all the .Net Framework source code.
  • Resharper 4 EAP delayed.
  • Lightspeed 1.2 released.
  • The rise of WPF vs WinFroms.
  • The Auckland dev community are slackers compared to Tauranga.
  • Vista SP1 and Windows 2008 RTM.


No doubt there will be plenty more.

See everyone next week!

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2008 Summer Road Trip - Day 1

So the  sun has set on day 1 of the Summer Road Trip 2008 in Auckland - The Presentation was done by JB, Chris and Myself this afternoon - it went very well, people enjoyed the content and the mix of integration, server management, database and development topics really meshed together nicely I thought...

There was enough to keep everyone interested, regardless of the hat you wear - and plenty of prizes too - well all love swag right?!

Big thanks to our MC Jaqcui, who handled the Intro and Outro and let everyone know about the local EllerslieCentral Auckland user group's - where I'll be sure to run a few sessions later in the year... and of course Darryl for handling some of the finer details like the venue, lunch, and the dinner afterwards - much appreciated.

For all those that came along - first off thanks for coming, obviously without participation in these events they'll just dry up and stop happening - and second don't forgot that there is no time like the present to start picking up these technologies and developing applications with and for them - the products are all but ready, so why can't you be (and not only are they great technologies, they're fun too).

The next presentation is in Tauranga - and there are still places left, so sign up here -
It's going to be on tomorrow (5th of Feb) at 1:00pm I believe.

And finally a short plug ;o)

For anyone that found this presentation interesting and would like to discuss the technical details of things like emerging technologies, general software Architecture, Developer Tools, Running software businesses etc.  I also organise the local
Sylvia Park Architecture Chat - which is a pretty casual meeting of some very smart people in the .Net Community.

We normally get together on a fortnightly basis at Garrisons in Sylvia Park and are always keen to have more people/fresh faces to come along and join in our discussions or even just float some development/architecture questions or problems you might have that the group can help solve - keep an eye on my blog, or the dot.net.nz mailing list for announcements of when we'll next be meeting up :)

And all are welcome of course!

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