The document discusses the ViewModel pattern in MVC applications. It explains that domain models returned from data access layers are not suitable for views. ViewModels are created to flatten and select only the needed data properties. Automapper is introduced as a tool to automatically map between domain models and ViewModels to avoid tedious mapping code. It provides features like projection, value resolution, null substitution and configuration with a fluent API.

1. The ViewModel Pattern Simone ChiarettaArchitect, Council of the EU http://codeclimber.net.nz Twitter: @simonech June 23rd, 2010

2. Who the hell am I? Simone Chiaretta Microsoft MVP ASP.NET ASP Insider Blogger – http://codeclimber.net.nz ItalianALT.NET UG Founder OpenSource developer Climber All Around Nice Guy Disclaimer:"The viewsexpressed are purelythose of the speaker and may not in anycircumstancesberegarded as stating an official position of the Council"

3. WhatisViewModel

4. Workflow of a MVC Application Controller asks for the data to the Model The request gets to the Controller Model 2 1 3 Controller Browser Model returns the data back to the Controller Controller formats data and sends them to the View View 4 5 View builds the page that is sent back to the Browser 3

5. Workflow of a MVC Application Controller asks for the DomainModel to the BLL The request gets to the Controller BLL 2 1 3 Controller Browser BLL returns the DomainModel to the Controller Controller formats DomainModelinto ViewModeland sends it to the View View 4 5 View builds the page that is sent back to the Browser 4

6. DomainModel != ViewModel DomainModel Data + Behaviours Hierarchical, complex types ViewModel Only Data Flat, only strings

7. WhyDomainModelisnotgood? Viewsshouldnotknowhowto traverse the DM Viewsusuallyneedlessproperties UsingORMsyoumight start a SQL querybymistake

8. Howto do it? Copy the propertiesneededfrom DM to VM Possiblyflatten data

9. DomainModel != ViewModel How to avoid getting bored writing tedious mapping code?

10. IntroducingAutoMapper

11. Automapper DevelopedbyJimmyBogard Latestrelease 1.1 Active Mailing list Downloadablefrom: http://automapper.codeplex.com/

12. Features Flattening Projection FluentAPIconfiguration Mapping of List and Collections Mapping of NestedObjects CustomTypeConverter CustomValueResolver CustomFormatters NullSubstitution

13. Basic Usage DefineMapping Mapper.CreateMap<Post, ShowPostModel>(); UseMapping Mapper.Map<ListModel, ListViewModel>(viewModel)

14. Projection Mapper.CreateMap<EditPageViewModel, Post>() .ForMember( p => p.Id, opt => opt.MapFrom(src => src.Post.Id))

15. CustomValueResolver Mapper.CreateMap<EditPageViewModel, Post>() .ForMember( p => p.Category, opt => opt.ResolveUsing<CustomResolver>() ) public class CustomResolver : ValueResolver<EditPageViewModel, Category> { protected override Category ResolveCore( EditPageViewModel source) { return new InMemoryPostModel() .GetCategory(source.Post.CategoryId); } }

16. NullSubstitution Mapper.CreateMap<Post, ShowPostModel>() .ForMember( p => p.CategoryName, opt => opt.NullSubstitute("No Category") );

17. Contacts – Simone Chiaretta MSN: simone_ch@hotmail.com Blog: English: http://codeclimber.net.nz/ Italian: http://blogs.ugidotnet.org/piyo/ Twitter: @simonech 16

18. Rating If you liked this talk, please consider rating it: http://speakerrate.com/talks/3670-the-viewmodel-pattern 17 Disclaimer:"The viewsexpressed are purelythose of the speaker and may not in anycircumstancesberegarded as stating an official position of the Council"