Tuesday, May 15

Keynote
Pablo Castro
by Tom Cooley

Tuesday morning kicks off the 2007 DevTeach Conference with Pablo Castro discussing the ADO.NET Entity Framework. Pablo is the technical lead for the ADO.NET team.

Whereas the current version of ADO.NET provides the ability to invoke commands against database connections, the Entity Framework uses code generation to turn tables and columns into objects and properties. While this initially reminded me of the code generation provided by strongly typed DataSets, the code generated by the Entity Framework uses partial classes that are easily extensible. Auto generated entities and associations are modifiable to enable custom views of the data for each particular application. And designers allow you to visually define and alter resulting generated code.

The framework abstracts the database objects such that a logical representation of a typical 1-many relationship looks like an object with a collection of related child objects. Table joins are hidden from the database developer by mapping the relations, called associations in EF, within an Entity Data Model.

The Entity Framework provides a number of features to make the sessions with the database work very naturally without writing a lot of configuration and connection code. This will hopefully dissuade developers from practices like hard-coding connection strings into the application.

Overall, this looks like an interesting data access technology and I am looking forward to how it looks when it RTMs.

LINQ: Introduction to Concepts & Advanced Concepts
Eric Moreau
by Martin Lapierre

This two-part session presented the new Language Integrated Query, that is, LINQ. It was a great thing that Eric decided to spend two sessions on this topic, because there was much to cover. In the first part he covered the overall technology and then went on with complete VB.NET demos in the second one.

A LINQ statement comes in many flavors, depending on each LINQ-enabled data source. Here is a VB.NET example of a simple statement for SQL:

	Dim contacts = _
		From c In Customers _
		Where c.City = "Hove" _
		Select c.Name, c.Phone
	

One very interesting feature of LINQ to XML is that it enables dynamic creation of Xml elements using Xml-like elements directly in our source code:

	Dim orders = From customer In customers...<Customers>, _
                  [order] In orders...<Orders> _
             Where customer.@CustomerID = [order].<CustomerID>.Value _
             Select <Order>
                        <%= [order].Nodes %>
                        <%= customer.<CompanyName> %>
                    </Order>
    

Many LINQ features that were missing last year are now available; including the ability to make insert, update and delete operations.

Finally, for those who would want to try LINQ, Eric pointed out that Visual Studio Orcas ships an updated version (April 2007) of the CTP for Visual Studio 2005 (May 2006).

Generics are, in my opinion, one of the best and most under-utilized features added to the .Net framework in version 2.0. Rob provided a basic overview on this topic to help overcome that issue. He started off by discussing how things were done before generics were available and the issues with casting and especially boxing value types.

Collections are one of the most obvious uses of generics, and Rob used that as the first sample to get everyone's feet wet. ArrayList was a common collection type used prior to the introduction of generics, which he used to demonstrate that there is no way to enforce strong typing on the members of the ArrayList. This could result in data inconsistency and worse, runtime exceptions that could have otherwise been caught during compile.

The pre-generic way to avoid these potential for runtime errors was to construct a custom collection class where the properties and methods that allowed adding and retrieving members enforced proper typing. This was cumbersome and not reusable resulting in a great deal of coding to ensure type safety.

By using generics, we can simply define a collection of a specific type. This is a much simpler implementation, prevents runtime errors, and also prevents the boxing/unboxing that occurs with value types.

Within the System.Collections.Generic namespace, the List<T> object is a generic-based replacement for the ArrayList. By convention, the type placeholder when defining a generic collection uses an uppercase "T" but any other letter or variable can be used in its place. For example a list of integers would be represented as

List<int> intList  = new List<int>();

Generics allow classes to be parameterized by the types they store and manipulate. While collections are a popular use of generics, they are extremely useful in defining general purpose classes that do not necessarily contain a list of items.

    public class Node<T>
    {
        List<Node<T>> _children;
        T _value;

        public Node(T value)
        {
            _children = new List<Node<T>>();
            _value = value;
        }

        public void Add(Node<T> node)
        {
            _children.Add(node);
        }

        public void Remove(Node<T> node)
        {
            _children.Remove(node);
        }

        public List<Node<T>> Children
        {
            get { return _children; }
        }

        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();
            sb.Append(_value.ToString());
            foreach (Node<T> child in _children)
            {
                sb.AppendFormat("\r\n  {0}", child.ToString());
            }
            return sb.ToString();
        }
        static void Main(string[] args)
        {
            Node<string> abcNode = new Node<string>("ABC");
            abcNode.Add(new Node<string>("DEF"));
            Console.WriteLine(abcNode.ToString());

            Node<long> longNode = new Node<long>(100);
            longNode.Add(new Node<long>(1000));
            Console.WriteLine(longNode.ToString());
        }
    }

Not only can classes be defined using generics, but methods within a class can be generic, providing flexibility in the types that can be passed to the method as parameters. This allows methods to be used against any types making them much more flexible.

But sometimes you don't want to make types and methods that are generic for any type. The framework provides constraints that you can place on the generics definition. You can constrain your generics in a few ways. You can do so by constraining the generics to be of a specific type or a type derived from that specified. Another method of constraining is by defining that the type passed in is either a value or a reference type. And finally, you can enforce that only types that have a default constructor provided are passed into the generics declaration.

The .Net framework provides a number of generic types and interfaces that can be used for your own generics to inherit or implement or to be used in constraining your generic types and methods.

Then Rob went into some of the details of using static members within a generic type. Each unique set of type parameters passed to a generic type declaration will share any static properties and methods. He demonstrated this with showing the IL code generated from two different instances of a class with a shared property count that was incremented in the type constructor.

Most of the new C# language features were made necessary by LINQ. What I really appreciated in this session was that Claudio showed us with many demos how each of these features can be used on their own.

The first feature was Automatically Implemented Properties; tired of writing setters and getters for each of your fields? Now you can simply specify the property name and the compiler does the remaining work for you (this doesn't work for read only properties):

public string MyTitle { get; set; } 

Claudio also demonstrated Type Inference with the new "var" keyword and the Extension Methods. These last ones are used to extend existing classes without altering their declaration. In one of the examples, we saw how a null reference could be used in this fashion without raising an exception:

// Here the Extension Method signature would be:
// public static string ToStringNullSafe(this object theObject)

object someObject = null;
Console.WriteLine(someObject.ToStringNullSafe());

Then Claudio presented Lambda Expressions, which can be seen as a simplification of Anonymous Methods, and how they are represented in Expression Trees. Here is an example of an Anonymous Method and its equivalent Lambda Expression:

List<int> evenNumbers = 
list.FindAll(delegate(int i) { return (i % 2) == 0; });

var evenNumbers = list.FindAll(i => (i % 2) == 0);

The last two features were Object Initializers, which are used to initialize any public property of an object at creation time, and Anonymous Types which are implicitly-named classes generated by the compiler. Finally, Claudio explained how all these features are relevant in LINQ and he concluded with this interesting piece of code:

var buttons =
    from control in this.Controls.Cast<Control>().OfType<Button>()
    select control;

foreach (var button in buttons)
    button.Enabled = false;

Brad started the sql-server-performance.com website roughly six years ago. He has since sold it but still contributes content to the site. He also acts as a consultant to Red Gate Software.

The Performance Dashboard is intended to augment Profiler and Performance Monitor to manage resource utilization. It helps to identify CPU utilization issues, waits, blocks and missing indexes. The dashboard does have some limitations, but given that this is a 1.0 release, that is not unexpected. It currently requires manual installation. The number of reports is somewhat small for this release. But this is essentially a preview of what is to come when Microsoft releases Katmai, the next version of SQL Server, sometime in 2008.

SQL Server 2005 SP2 is required for the performance dashboard to be installed. It is essentially a series of pre-defined reports using the Custom Reports feature introduced in SP2. The download is 1.4 MB. Running the install creates a folder with the report definitions, a SQL script which must be run for each database instance in which you want the dashboard to run, and a help file which is a worthwhile read. Brad also recommends spending time with the SQL script file as well because this provides some insight into the use of some obscure and even undocumented DMV usage.

After going through the PPT deck, Brad switched into demo mode. To demonstrate some of the performance reports, he intentionally placed his database server under a heavy load.

Once launched, the dashboard displays a main report that acts as an entry point to the other, more detailed reports. The main report includes a chart showing the last 15 minutes worth of CPU utilization. By clicking within the graph, another report providing more detail is displayed. Included in this detailed report are the top 15 busiest queries. By that it means most often run queries. Each query provides lots of detail such as total number of milliseconds all executions of the query ran as well as max execution time, average execution time, number of logical reads, etc. You can also get the execution plan from the report. It is currently only the text version, but you can alter the report definition (rdl) file to use SHOWPLAN XML instead.

The Wait States section of the main report allows you to drill into the details of all wait states that have occurred since the database instance was last started. The Sleep wait state is common and not really an issue. Typically this will be the greatest amount of waits listed on the report. You can generally ignore this and move onto the other wait states with a high occurrence. Watch the ones that actually affect system resources such as Disk I/O, Network I/O, and memory. This can help you identify the bottlenecks in your system.

The Historical I/O report is also helpful in determining which databases are incurring the most I/O. It even shows both I/.O utilization of the transaction log. Included in this report is a list of missing indexes that the optimizer has logged as having been beneficial if they had been present. It will identify covering indexes using the new INCLUDE clause of index creation.

Brad recommends the Duration and the Logical Reads reports as being some of the most useful in determining performance issues. The Active Trace report is also informative. By default, SQL Server 2005 starts at least one trace which could be optionally disabled to improve performance on busy production servers.

I found this to be an interesting topic covering a much needed tool in performance tuning our databases. I only wish it were available during my last project.

Wednesday, May 16

Configuration Management in .NET (Fundamentals)
Don Kiely
by Martin Lapierre

I decided to write about this session because it contained basic material that every developer should know about configuration even if it's been around for awhile. As an introduction, Don made an overview of the .NET configuration system and explained how an app.config or a web application web.config file overwrites the default configuration information of the machine.config and root web.config files. He later demonstrated this by displaying the content of a merged file generated by the WebConfigurationManager using code similar to this:

string sFile = @"C:\Samples\full.web.config.xml"; 
Configuration  config =     
  WebConfigurationManager.OpenWebConfiguration(
   "/ConfigASPNET" ); config.SaveAs( 
   sFile, ConfigurationSaveMode.Full, true ); 

The System.Configuration and System.WebConfiguration namespaces provide the classes that we can use to read, manipulate and modify configuration data. A web or a windows application uses a configuration manager to access either the default or a specific configuration file. The Xml content of the file is then translated into strongly-typed configuration objects such as sections, section groups, section properties and collections. Here's an example of how to read and access a property of the identity section in a web.config file once it has been loaded as an object:

Configuration config = 
  WebConfigurationManager.OpenWebConfiguration( "/ConfigASPNET" ); 
IdentitySection identitySection = 
  ( IdentitySection )( config.GetSection( "system.web/identity" )
txtResults.Text = 
  "Impersonate is set to " + identitySection.Impersonate.ToString(); 

The most useful thing in the .NET 2.0 configuration features is that we can define our own configuration sections, collections and properties by creating custom section handlers. When creating section handlers, we can define properties declaratively or programmatically. In the fist case, we use the ConfigurationPropertyAttribute attribute to declare a property:

[ ConfigurationProperty( "Information", IsRequired=true ) ]
public string Information 
{ 
    get { return this[ "Information" ].ToString(); } 
    set { this[ "Information" ] = value; } 
}

And when doing it programmatically, we can take advantage of validation attributes, a feature which is not available declaratively:

[ RegexStringValidator( @"^\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}$" ) ]
public string Information 
{ 
   get { return this[ "Information" ].ToString(); } 
   set { this[ "Information" ] = value; } 
}

Don's demos also efficiently showed how to create complete sections, section elements and collections by deriving classes from ConfigurationSection, ConfigurationElement and ConfigurationElementCollection. His demos were simple and easy to follow, and were provided both in VB.NET and C#.

Rob is the director of Application Architecture for monster.com and hosts the website designpatternsfornet.com

Looking back at the past, there have been a number of attempts to solve the problems of application complexity and interoperability. Each step has been evolutionary in nature. Windows DNA and COM promised many of the same solutions that all the hype of SOA claims. These include service reuse, reduced development cycles, and cost efficiencies.

SOA makes the same claims that were promised more than 10 years ago. Vendor neutrality, software versioning, better data integrity, performance, and scalability are more claims made by the SOA pundits.

Part of the problem with SOA is that the term itself gets redefined by vendors to match their product offerings. According to Rob, SOA is really just "a design style which promotes the delivery of software operations that usually complete some unit of work." He outlined four tenets of service orientation espoused by Microsoft: Boundaries are explicit Services are autonomous Services share contracts Compatibility is policy-based

Yet Microsoft breaks some of these tenets themselves. For example, DataSets are commonly returned from web service calls, yet that is platform specific and therefore incompatible with other service consumers implemented on another platform such as Java.

A key concept to SOA is the contract. A service exposes the contract to consumers. Consumers must know the contract, policies associated with it, as well as the proxy to connect back to the service endpoint.

Most people believe SOA and web services are synonymous when in fact web services are merely a common implementation of service orientation. Another common misconception is that SOA guarantees loose coupling. However, it goes back to the contract. If the service must make a change, either in the service contract or in its policies, you require a change to the consumers of that service. That is a form of coupling. Most of the promises of SOA are not really attained simply by following SOA. Many of the claimed benefits of reuse and ease are not really gained by service orientation per se. Of these promises, platform and vendor independence are the easiest to attain through service orientation. But many of the proclaimed benefits are not solely within the domain of SOA. In fact the performance gains claimed are really hard to attain. In most cases, public services use http as its protocol which is inherently slow an unreliable.

But this talk was not just an attack on SOA. Instead, it was intended to tear away the hype and debunk the myths, while looking at the real opportunities that a service oriented architecture can provide.

Some of the more realistic goals for SOA include smaller, more discrete assemblies which equate to smaller memory footprint and faster build times. SOA can certainly aid in providing highly scalable solutions, though it is not the only factor involved. Separation is also an attainable goal using service orientation. And although performance is generally not considered a strong characteristic in many cases, WCF addresses many performance issues by providing faster, more efficient transports.

For me, the take-away was to evaluate SOA on its technical merits and to try to ignore the hype. I think this was Rob’s primary objective for the session.

In general, the goals of asynchronous programming are to enable parallel processing of an application's operations, to make a user interface more responsive to user input and to make a system take advantage of multiple processors. Although this session covered how to develop asynchronous operations in ASP.NET 2.0, some of the techniques presented by Julie could also be used in non-web applications to achieve these same goals.

Traditionally, ASP.NET will answer a request by taking a thread from the web application thread pool and by executing code synchronously on that thread until the response is sent to the client. If an external or remote process (such as a database server) is called during the code execution, the thread from the thread pool will be locked and unavailable to answer other requests. By implementing asynchronous operations, we can make ASP.NET free up the thread without waiting for a lengthy operation to complete; when that operation ends, ASP.NET will take another thread from the thread pool and will continue answering the initial request.

Julie first demonstrated two ASP.NET techniques to integrate asynchronous calls in a web page. The first one was to set the "async" property of a page to "true" and to use the Page.AddOnPreRenderCompleteAsync method to register callbacks for the beginning and the ending of the asynchronous operation. Implementing this technique may not be the best practice to follow, because it is limited to one asynchronous call. If you have multiple asynchronous calls to make in parallel, it's better to use the other technique: asynchronous tasks. You first create your callbacks and an instance of a PageAsyncTask, which will contain the handlers to your callbacks and some extra information for the behavior of the asynchronous operation. Then you register the task to the page using Page.RegisterAsyncTask – doing it multiple times if you have many operations to execute concurrently.

' Registering an asynchronous task.
Dim task As New PageAsyncTask( New BeginEventHandler(AddressOf BeginLongProcess), _
                               New EndEventHandler(AddressOf EndLongProcess), _
                               New EndEventHandler(AddressOf TimedOut), Nothing, True) 
Me.RegisterAsyncTask(task)

Julie also covered asynchronous Web Services and asynchronous data access. A .NET 2.0-generated Web Service proxy always comes with synchronous and asynchronous methods. The great thing is that the mechanism is implemented with events and not with callbacks implementation. So, when calling a Web Service asynchronously, all you have to do is to register your event handler to the method-completed event and call the asynchronous method:

Private ws3 As localhost.SlowService
 
Protected Sub Button1_Click(ByVal sender As Object, _
                            ByVal e As System.EventArgs) Handles Button1.Click
    ws3 = New localhost.SlowService
    AddHandler ws3.ThreeSecondHelloCompleted, AddressOf ThreeSecondCompleted
    ws3.ThreeSecondHelloAsync()
End Sub

Private Sub ThreeSecondCompleted(ByVal sender As Object, _
                                 ByVal e As localhost.ThreeSecondHelloCompletedEventArgs)
    lblmsg.Text = e.Result
End Sub

Finally, asynchronous data access is made available thru SqlCommand and the BeginExecute/EndExecute prefixed methods, which work with callbacks similarly to ASP.NET.

This is obviously a hot topic because the room was completely packed. And to encourage people to fill out their evaluations, Jean-Paul, offered free licenses to ReSharper to the first five people who submit their comments.

The prerequisites for this topic are an understanding of the dependency inversion principle and dependency injection. The basic principle is that "high-level components should not depend on low-level components; they should both depend on interfaces."

Jean-Paul provided some recommended resources on design patterns including HeadFirst Design Patterns . Despite the fact that all of the samples are written in java, it is a very well written book and is an easy read. The language implementation is irrelevant to the patterns being described.

Jean-Paul demonstrated a poorly architected web form that has several responsibilities that it should not, such as opening a db connection, getting raw db data, and mapping it to a list of employee objects. In refactoring the sample application to focus each layer on its own responsibilities, Jean-Paul introduced the Passive View design pattern.

The Passive View deign pattern attempts to relegate UI to the responsibility of accepting user input and displaying output. PassiveView is a form of Model-View-Presenter. By refactoring the additional behaviors out, we achieve greater separation and more resilient components. The Presenter in this pattern will use indirection to abstract the final UI technology from the service we’re developing. Passive View uses an Observer model. The view implements an interface that among other things, defines an event. The Presenter subscribes to these events.

The initial refactoring only took us so far though. It essentially removed the additional responsibilities out of the web page and into the Presenter in the Passive View. Now the Presenter has too many responsibilities. To correct this, Jean-Paul used the Service Layer pattern, an implementation of the Gang of Four Façade design pattern. This pattern also uses interfaces to provide a layer of abstraction between the service layer and its consumer.

Yet, once again our refactoring was not complete, the higher-level components of View and Presenter had been successfully decoupled from the lower-level components, but the new service layer still had an added responsibility of mapping data returned from the database to the domain objects. This was to be solved by the Data Mapper Pattern.

Unfortunately, several questions from one member of the audience detracted the session to the point where Jean-Paul was unable to finish his presentation in the allotted time. Luckily, the May/June edition of CoDe Magazine contains an article Jean-Paul wrote which appears to cover everything in the presentation. And given that this magazine was included with the DevTeach packets handed out at registration, we all have access to what I thought was a valuable talk.

Thursday, May 17

Building Silverlight Applications using .NET (Part 1 & 2)
Yair Alan Griver
by Martin Lapierre

This was yet another great two-part session. Yesterday, Yair Alan Griver did quite an introduction of the flashy Microsoft Silverlight and continued today by using .NET 3.0 and LINQ features right into that new technology. So new in fact that Alan just had a few days before DevTeach to build up his presentation - and he did quite a good job.

But wait a minute - what is Silverlight?

Silverlight is a new Rich Internet Application (RIA) technology which comes in the form of a web browser plug-in. It offers a subset of the Windows Presentation Foundation (WPF) that can run inside a browser. We could think that Microsoft just decided to bring back the old ActiveX technology, but we’d be wrong. Silverlight is much, much more than that: the plug-in can be installed on either Windows or Mac OS X and supports Firefox, Safari and Internet Explorer.

XAML is at the root of the Silverlight technology (XAML is the XML-based document format that is also used by WPF and tools like Microsoft Expression Design and Microsoft Expression Blend). This means that a web designer can work in graphical tools to create his user interface and save that in a XAML document onto which web developers can hook server code and events. Developers can even modify the XAML document and the changes will be reflected back in the web designer tools.

So, are Silverlight and XAML meant to replace ASP.NET and HTML? The answer is no, or not yet. In the current beta version, Silverlight doesn’t provide a rich set of controls; the 1.1 alpha version may not even ship a textbox! In fact, the user interface is specified with shapes (Rectangle, Ellipse, Line, etc), which can be made to represent complex objects.

A Silverlight application can be interacted with and embedded in an ASP.NET and an ASP.NET AJAX application using JavaScript; the Silverlight plug-in exposes its internal Document Object Model (DOM) to the browser, which makes this possible. Here is an example where a Silverlight "control" is used in an HTML page which also contains a textbox and some JavaScript invoking one of the Silverlight control method (code edited out for clarity):

<cc1:Xaml ID="Xaml1" runat="server" Height="798px"
 Width="1002px" Windowless="true" XamlUrl="~/Page.xaml"/>

<input id="Text1" type="text" />

<script type="text/javascript">
function Search()
{
var input = document.getElementById("Text1");
var control = document.getElementById("Xaml1");
		    
//Call the scriptable event
control.Content.BaseballData.Search(input.value);
} 
</script>

Although Silverlight cannot be used to create 3D, out-of-browser and off-line applications, it is a beta technology that is worth following, as it promises wonders for the future of web development.

You often read articles on 'best practices' for performing various tasks, but it is rare to hear the other side of the coin. Roman and Peter collaborated on a list of the traps and pitfalls to avoid when designing and developing database systems. This was a fun session highlighting some of the “Stupid Human Tricks” we that call ourselves database professionals may have performed throughout our illustrious careers. I personally have never done any of these worst practices. That’s my story and I’m sticking to it. The session is broken out into three main topic areas, Administration, Database Design, and Programming.

Peter asked for a show of hands on how many people perform backup on their databases. More or less all hands (of dba's responsible for such a task) went up. He followed on with how many verify their backups. Some hands went down. He then asked how many have performed a test restore. More hands went down. The point being is that disaster recovery cannot be an afterthought. Failure to plan is a plan for failure. Backup your databases, make sure the Verify option is turned on for those backups, and perform a test restore as part of your disaster recovery plan.

From the security standpoint, mixed mode security should be avoided if at all possible. Using 'password' as your password, especially for the 'sa' account, is obviously a worst practice. Likewise, using the sa login within the application is a bad idea. Even granting a login dbo access on a database is also generally granting more privilege than necessary.

When updating production databases, and even non-production ones, you should never just use things such as the table design GUI to execute these changes. It is fine to use the GUI to generate a script, but the script should be verified to ensure the functionality will occur as you expect. Then you should thoroughly test the scripts before executing in a production environment.

On to database design. Databases contain tables. That's plural - with an s. When creating a database, don't try to stuff all of your content into one table. That's what they built Excel for. If you've been bold and wise enough to create more than one table in your database yet do not enforce referential integrity via foreign key relationships, you are asking for data integrity issues.

SQL Server automatically makes primary keys clustered by default. This can be convenient in many cases. But you should not just accept that the PK is always the best choice for your clustered index. You only get one. Choose wisely. When scripting database objects, it is important to be explicit.

When naming stored procedures, do not use sp_ as the prefix. Doing so will cause SQL Server to look first in the system database thereby incurring a performance hit.

When naming tables, choose whether or not to pluralize table names or not. There is debate on which is proper. Is it Customer or Customers. In fact, this is one point where Roman and Peter disagree. Roman, who is on the pro-plural side stated, "When I go to the store to buy cereal, I don't get a box of Rice Crispy." The point is choose one and be consistent. Also, prefixing objects with things like "tbl" has gone out of style. Like bell bottoms and platform shoes, Hungarian notation is a mistake of the past that should not be repeated.

Don't stuff character fields consisting of numbers into numeric data types. This includes phone numbers, zip codes and social security numbers. Numeric data types are intended to perform mathematical operations. When was the last time you needed to average phone numbers or sum zip codes? These are character fields. They just happen to be limited to characters 0 – 9.

There is no longer any reason to use text, ntext and image data types when developing new applications against SQL Server 2005. Varchar(max) and its Unicode counterpart are preferable.

On the programming side, the recommendation is to no longer hand code standard CRUD procedures. There are many code generation options available that build the scripts for you. Other practices that are now obsolete are to replace @@ERROR with TRY/CATCH and replace @@IDENTITY with scope_identity.

SQL CLR is not the new T-SQL. T-SQL is still the preferred language at least for set based operations. CLR programming can be powerful but its usage should be closely scrutinized.

Thanks to Roman and Peter for pointing out my...I mean the other attendee's shortcomings. I'm off to go test my backups.

This year, the DevTeach conference also includes the SQLTeach conference. My coverage couldn’t have been complete without a few words on a SQL session. I have decided to talk about Peter DeBetta's presentation of the integrated features of XML, because XML is now critical to so many applications that it just makes sense to discuss it from a developer point of view.

SQL Server 2005 can handle XML as a native data type. I said "can", because if you store XML documents in your database without any need to validate or perform queries on them, it is more efficient to simply store them as good-old binary fields. But otherwise, the XML data type is your new best friend; it can support an XML document of up to 2GB and can be associated with an XML schema to make sure that only valid XML documents are inserted in your database. Where data manipulation is concerned, the XML data type can be converted to/from character and binary types and supports advanced querying capabilities thru XQuery and XPath 2.0. Note that an XML column can only be indexed using an XML index.

When creating a table with an XML column, it is possible to create a constraint between the table's primary key and the content of the XML document. In the following code snippet, the constraint forces the ResumeID column to must match the ResumeID attribute of the xml document:

CREATE TABLE ContactResume
(
ResumeID int NOT NULL PRIMARY KEY,
Resume xml(xscResume),
CONSTRAINT ckResID CHECK(ResumeID = 
Resume.value('Resume[1]/@ResumeID','int'))
)

The XML data type also comes with a predefined set of methods: exist(), value(), query(), modify() and nodes(). They can be used in T-SQL statements to get, test or modify the XML content.

One very precious piece of information Peter gave about XQuery was that we can actually use variable or column values in query expressions, which may help to remove the need for dynamic SQL. The next example is taken from the SQL Server 2005 Books Online, as the session scripts were not available at the time of this writing:

SELECT P.ProductID, CatalogDescription.query('
declare namespace pd="http://schemas.microsoft.com/sqlserver/
 2004/07/adventure-works/ProductModelDescription";
       
  
    {
if (not(empty(/pd:ProductDescription)))  then
attribute   ProductModelName { /pd:ProductDescription[1]/@ProductModelName }
else () }

') as Result
FROM Production.ProductModel PM, Production.Product P
WHERE PM.ProductModelID = P.ProductModelID
AND   CatalogDescription is not NULL
ORDER By PM.ProductModelID

Peter also covered many of the FOR XML enhancements, which can be used to generate XML from the standard and XML data types. They provide much more flexibility than in SQL Server 2000 and are worth investigating on your own if you need to return customized XML output.

This concludes my DevTeach 2007 coverage. I'd like to thank Tom Cooley for his contribution to this experience and for having the patience to edit, format and upload the articles so that they could finally made their way to Universal Thread.

Julie's goal for this talk was to expand upon and dig deeper into the topic of the Entity Framework overviewed by Pablo Castro in the Keynote Address. Since much of this talk is about the Entity Framework, Julie (with tongue in cheek) struck out Orcas from her slide title and placed Katmai in its place because Microsoft just announced that this feature will be delayed to the Katmai timeframe.

Speaking of delays, as Julie began her presentation and had barely made it to the second slide, one of the hotel organizers came in and announced that we needed to relocate to another room. Le Caf Conc, which I'd heard at least one speaker refer to as the "Muppet Theatre", was apparently being used for a dinner later and the staff needed to prepare the room. We all packed up our stuff and shuffled across to the main hall, only to realize that no projector or screen was available.

With a lot of content to cover and time already wasted on the relocation, Julie hopped up on the stage and continued her talk without the visual aids. Meanwhile hotel staff brought in the projector equipment and setup around her. All of this provided quite a distraction but I have to give Julie credit for handling it so gracefully. Now on to the content itself.

As stated above, this talk was an expansion of the overview provided during the Keynote, but Julie also provided a brief overview of the main points covered by Pablo as a foundation before drilling in deeper (see the Keynote session for more details). Note that this is a very big topic and essentially amounts to a paradigm shift in the way we will with data from an applications perspective.

One goal of the Entity Framework is to provide to the application developer an object model that more closely represents the problem domain being addressed. It does this by translating highly normalized database tables with complex relationships into entities with properties to represent table columns and associations to related tables. The framework is based upon the concept of Entity Data Modeling. The Entity Data Model (EDM) defines three Xml files that describe each entity and relationship, the physical storage of the tables and columns, with data types, foreign key constraints and cardinality, and a list of mappings between each entity and its storage representation.

A wizard interface is provided for connecting to the database and generating the Entity Data Model. An entity connection string provides much the same information as a standard connection string, but also contains additional metadata used to aid in creating the Entity Model. After the desired tables are selected the wizard creates the model as the three Xml files listed. Because this is beta software, tooling is still limited. Julie spent some time walking us through the Xml files generated to help provide an understanding of the plumbing underneath the model.

 There are many levels of abstraction within this framework. It can be as easy as dragging an entity onto a form control and setting a few properties. Or you can generate an object data source from the EDM. Note that an Entity is much like a Data Transfer Object (DTO) in that it only had properties that represent the values of the entity. The object data source is a partial class that can be extend with additional properties and behaviors. This level of abstraction makes programming against the database far easier to do. The plumbing code is generated and can be run without modification if you like.

Julie also spent time talking about LINQ and its various flavors, including LINQ for Objects, LINQ for Entities and LINQ for SQL. LINQ for Entities will allow developers to interact with the Entity Framework, producing strongly typed objects and collections from the Entity Sets.

The Entity Framework will also provide an API to program against EDM objects using an EntityClient, much like the SqlClient available in current versions of ADO.NET. This will allow you to begin using entities and the EDM while still using code that returns IDataReader.

All the functionality in ADO.NET 2.0 is still there. This should allow developers to ease into this new paradigm while preserving existing code bases. At present, for myself and most of the attendees, there is a lot of information to digest regarding the Entity Framework and all of its new syntax and object types. Yet I suspect in another year or so, this will all seem so normal and we’ll wonder how we ever worked with that database before.