Building an enterprise app in silverlight 4 and NHibernate

Building an enterprise application with Silverlight and NHibernate
Gill CleerenMicrosoft Regional Director/MVP ASP.NETVisugUsergroup lead - Ordina
www.snowball.be
Bart Wullems
MCT, MCPD
Application Architect Ordina
bartwullems.blogspot.com

Agenda
Building the foundation
CQRS
OData
NHibernate
Building the front-end in Silverlight
MVVM
What is MVVM?
Why and why not
The parts of MVVM
Implementing MVVM principles
Demo
Finding your VM using MEF
Commanding
Communication between VMs

Scenario:
Planning your vacation
with NHibernate and Silverlight

Building the foundation

Bye bye 3-tier

What is CQRS?

CQS Defined
Bertrand Meyer (via Wikipedia)
“Command Query Separation”
“every method should either be a command that performs an action, or a query that returns data to the caller, but not both. In other words, asking a question should not change the answer.”

CQRS defined
Meyer:
Separate command methods that change state from query methods that read state.
Greg Young:
Separate command messages that change state from query messages that read state.
Can have significant architectural implications

Welcome CQRS

Queries
Simple Query Layer
Simple views or sprocs or selects from denormalized tables
Simple DTOs, no mapping needed
Don’t go through the Domain Model, as it pollutes it
ViewModel per query perhaps
Why should the data come across 5 layers through 3 model transformations to populate a screen? (Udi)
Synchronous, no messaging needed

Commands
Commands capture intent, DTOs don’t
CustomerDTOvsCustomerChangedAddressCommand
Handler per command
Can be validated outside of domain entities
This is why domain entities are never invalid, commands that would produce invalid state are rejected

Commands
Separate Data Modification
Make preferred
Change address
A generic DTO could do these things, of course, but after the fact, how do you know what actually happened?
UI Implications
Grid-like screens don’t work
Commands require specific intent

How do we implementthis?

Implement the query model usingodata

OData.org

A RESTful Interface for Data
Just HTTP
Data as resources, HTTP methods to act on it
Leverage caching, proxies, authentication, …
Uniform URL syntax
Every piece of information is addressable
Predictable and flexible URL syntax
Multiple representations
Use regular HTTP content-type negotiation
AtomPub, JSON

Model and Operation Semantics
Underlying data model
Entity Data Model
Entities Resources
AssociationsLinks
Operation semantics
Mapping of HTTP methods
GET  Retrieve resource
POST Create resource
PUT  Update resource
DELETE Delete resource

WCF (Data) Services
WCF Data Services
WCF Services
REST
AtomPub
OData
SOAP
WS-Security
WS-*

WCF Data Services
HTTP
Data Services Runtime
Reflection Provider
.NET Classes [+ LINQ provider]
Data Source(IQueryable)

oData and Silverlight
Accessing Data Services
Silverlight ClientHttp stack still an option
Data Services Client more usable as it knows the details of the data service interface
Features
Full abstraction on top of the service – no need to deal with HTTP, serialization, etc
Data as objects with automatic change tracking
LINQ for queries
Data-binding friendly interfaces
Work same-domain and cross-domain

CQRS and OData
OData
21

Demo
UsingOData to implement the query part of CQRS
22

Implement the domain model usingnhibernate

NHibernate
Full-featured ORM solution
Open source
Based on Java’s Hibernate framework
Uses XML(by default) to map tables/columns to objects/properties

NHibernate API

NHibernateQuickstart
Create hibernate.cfg.xml or use app.config
varcfg = newConfiguration();
cfg.Configure();
varsf = cfg.BuildSessionFactory();
using(var s = sf.OpenSession())
using(vartx = s.BeginTransaction())
{
var c = s.Get<Customer>(42);
tx.Commit();
}

WhyNHibernate?
EntityFramework
GreatforRapidApplicationDevelopment
Falls short forEnterpriseApplicationDevelopment
NHibernate has
More maturity
More flexibility
Betterextensibility

CQRS and NHibernate
NHibernate
NHibernate
29

Convention over Configuration
FluentNHibernate
http://fluentnhibernate.org
Replaces
XML mappingbyfluentmapping
XML configurationbyfluentconfiguration
Advantages
Type safety
Removestedious XML mappings
Intuitive interface
Conventions

AutomaticSession management
DataContext per Request
IServiceBus
Request 1
Session 1
DB
Session 2
Request 2

Demo
Using NHibernate to implement the domain part of CQRS
32

Building the front-end in Silverlight

What is MVVM?

Understanding MVVM
MVVM :
is an architectural pattern created by John Gossman from WPF team
is a variation of MVC pattern
is similar to Martin Fowler’s PresentationModel pattern
works because of Silverlight data Binding & commanding
is typically used in WPF/SL-applications to leverage the power of XAML, so that Devs and Designers can work together easier
35

Understanding MVVM

Why and why not MVVM?

Why MVVM
Better SoC (Seperation of Concerns)
More maintainable
Model never needs to be changed to support changes to the view
ViewModel rarely needs to be changed to support changes to the view
More testable
ViewModelis easier to unit test than code-behind or event driven code
Eliminates the need to do code behind which leaves the UI all in XAML
38

Why MVVM
Because the framework (SL & WPF) have the power to support it
Databinding/DataContext
Increases the "Blendability" of your view

Why not MVVM
Lack of standardization so everyone has own favor
Message to community is not clear!!
For simple UI, M-V-VM can be overkill
Too much code needed
INotifyPropertyChanged
Commands
40

The parts of MVVM

What we all do…
All UI code in code-behind
View
XAML
Data Model
Code-Behind
Event Handlers

The MVVM way
View
XAML
Code-Behind
Change notification
Data-binding and commands
View Model
Data Model
State + Operations

The parts of MVVM
View knows ViewModel
ViewModel knows Models
But not vice versa.
View
ViewModel
Model
44

The View
The view
represents the user interface that the user will see.
can be a user control or Data Template
shouldn't contain any logic that you want to test
should be kept as simple as possible.
45

The ViewModel
An abstraction of View
Connector between View and Model
Make VM as testable as possible
46

The Model
Can be Data Model, DTO, POCO, auto-generated proxy of domain class and UI Model based on how you want to have the separation between Domain Service and Presentation Layer
No reference to ViewModel
47

Where to start?
BING (or google is fine as well )
MVVM Light Toolkit
Prism
Caliburn
48

Demo
Let’s take a look at an MVVM implementation
49

Implementing MVVM principles

View model base class
Implements INotifyPropertyChanged
Contains base code for all VMs to re-use
51

Demo
BaseViewModel
52

Which comes first...
2 options:
View first
ViewModel first
53

ViewFirst
Based on XAML mostly
The View has a relationship to its ViewModel (usually through data binding).
DataContext={Binding ...}
Available at design time (Blend support)
54
View
<UserControl.DataContext>
<dive:PageViewModel />
</UserControl.DataContext>

ViewModel First
The ViewModel creates the view
usually through an IoCcontaineror MEF
55
View Model
public MyViewModel(IMyViewmyView)
{
myView.Model = this;
}

How to implement this?
Locator pattern
Implemented through a class that contains all VMs as static properties
An instance is then made available as Resource
All Views can bind, no code needed in View
 Clean way
Not good since all VMs need to be known upfront
Property for each available VM
Difficult if application is MDI-like (more than one instance available)
56

Demo
Locator
57

How to implement this?
MEF
Based on
Import: class says it needs an instance of a specific type
Export: class says it wants to be made available for composition
Composition: MEF links imports and exports together
Can create one shared instance or dynamic number thereof
Solves earlier problem
Easy for testing and mocking
58

Demo
MEF
59

Commanding
Instead of having event handlers in code-behind, we use commands
SL4 has the ICommand interface
Execute method
CanExecuteproperty
CanExecuteChangedevent
Way to create commands:
Write ICommand implementation
Create instance on VM
Bind Command property of control to this instance
60

Commanding
Commanding is supported on ButtonBase
Button, HyperlinkButton
Not on others like ComboBox SelectionChanged
Can be solved with event triggers
Can be added on every event
Part of System.Windows.Interactivity
Can be bound to every control

Demo
Commanding
62

Communication
63
View Model
View Model
View Model
View Model
View Model
View Model
View Model
View Model

Communication
64
View
View
XAML
XAML
Code-Behind
Code-Behind
View Model
Data Model
View Model
State + Operations
Data Model
State + Operations
Message
Publish messages
View
XAML
Code-Behind
Subscribe to messages
Event Aggregator
View Model
Message
State + Operations

Communication
VM’s need to be able to talk to each other, eg: send messages to each other
Not a good idea to have each VM reference all other VMs
Solution:
Event Aggregator/mediator/messenger
VM can register to receive messages of a certain type (for example string messages)
Another VM can register with the same messenger to send messages
This allows both VMs to communicate with each other without tight coupling
65

Demo
Messaging between VMs
66

Some tips to take home
Use MVVM in Blend
In View’s constructor, check DesignerProperties.IsInDesignTool
Unit testing
VMs can easily be unit-tested
Silverlight Unit Testing Framework ships with Silverlight 4
Can be used from the browser
No real way to integrate with automated testing (MSBuild) yet
67

Demo
Unit testing
68

Summary
CQRS
Gives the necessary level of scalability and maintainabilityforenterpriseapplications
oData is greatfor the query part
NHibernate rocks for the command part
MVVM
Create better testable applications
Works for both Silverlight and WPF

Questions?

http://randomware.blogspot.com	1480
http://bartwullems.blogspot.com	105
http://randomware.blogspot.it	43
http://blogs.msdn.com	23
http://translate.googleusercontent.com	3
http://twitter.com	2
http://bartwullems.blogspot.co.uk	2
http://bartwullems.blogspot.com.es	1
http://bartwullems.blogspot.com.au	1
http://bartwullems.blogspot.fr	1
http://bartwullems.blogspot.in	1
http://www.slideshare.net	1
http://webcache.googleusercontent.com	1
http://bartwullems.blogspot.ca	1

Building an enterprise app in silverlight 4 and NHibernate

by bwullems on Jun 30, 2010

Accessibility

Categories

Tags

Upload Details

Usage Rights

14 Embeds 1,665

Statistics

Building an enterprise app in silverlight 4 and NHibernate — Presentation Transcript