Inverting Control in WCF

Inverting Control in WCF
Chris Deweese
photo by brentdanley via Flickr

About Chris Deweese
.NET Developer/Architect
Specialties: SOA, Xml, Distributed Messaging, Object-Oriented Design
Primarily work on System Integration & Information Sharing projects
2009 Microsoft MVP, Solutions Architect
Twitter @cdeweese
http://christopherDeweese.com/
Avid Xbox player (when kids are sleeping)

At a Glance
Brief overview of Inversion of Control
The “container”
Quick Overview of WCF Hosting Environment
Short Overview of WCF Extensibility
Where to invert control in WCF
Ode to Code
Review

Wikipedia: Inversion of Control
In object-oriented programming, the dependency inversion principle refers to a specific form of decoupling where conventional dependency relationships established from high-level, policy-setting modules to low-level, dependency modules are inverted (e.g. reversed) for the purpose of rendering high-level modules independent of the low-level module implementation details. The principle states:
A. High-level modules should not depend on low-level modules. Both should depend on abstractions.
B. Abstractions should not depend upon details. Details should depend upon abstractions.
http://en.wikipedia.org/wiki/Dependency_inversion_principle

English […]! Do you speak it?
Reduce coupling between modules (classes, components, subsystems, etc) by using abstractions (interfaces, base classes).
Modules built to require dependencies be provided.
At runtime the dependencies will be provided so the module can do it’s job.
Example: Class PersonService requires an IPersonRepository instance in order to perform its work.

The “Container”
Inversion of Control containers are a pattern to implement the dependency inversion principle.
The “container” is used to locate dependencies typically by type <T> or type <T> + a unique key.

Containers for .NET
Structure Map
Castle Windsor
Unity
Spring.Net
AutoFac
Ninject
… Others via Scott Hanselman’s Computer Zen

WCF Hosting Environment
Service instances hosted inside a service host and service context
Service Instance Provider responsible for managing service instance lifetimes
If service instance faults the service host will abort and destroy the instance
Default is per call instancing, i.e., every call to your endpoint creates new instance of your service*
*This is probably a key point.

WCF Hosting Environment

WCF Extensibility
WCF Extensible through many means
Behaviors, Instance Providers, Hosts, Dispatchers, and more. All done via:
Overriding Base classes
Implementing Interfaces
For Today’s discussion we’ll focus on Service Behaviors, Instance Providers, Service Hosts, and Service Host Factories

Service Behavior?
Controls the local execution of a service
Applied to alter the services behavior at runtime
Service Behavior must implement System.ServiceModel.Description.IServiceBehavior.
Service Behavior applied through code by a custom service host or through configuration.

“Best” location to attach container?
In WCF, for a container to serve all instances it must be hosted at the Service Host level
The container will be available to pass dependencies to the service instances at runtime
Created once and serves all instances of the service

Ode to code.
photo by Premshree via Flickr

The Solution
Custom Instance Provider
Provides instances of your service class to the WCF Runtime.
Custom Service Behavior
To substitute your instance provider for the default one.
Custom Service Host
Controls the container.
Custom Service Host Factory
Initializes container, creates custom service host and passes container to custom service host.

Discussion/Questions
Thanks for your time. Let’s talk if you have any tips or questions.

Inverting Control in WCF

by Chris Deweese on Nov 19, 2009

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