Slide deck presented to LA SQL Developers Group on Thursday, March 15, 2012

1. James Johnson, MVP

2.  Founder and President of the Inland Empire .NET
User’s Group
 Three time and current Microsoft MVP – CAD
 Software developer by day
 Serial netrepreneur by night

4.  Entity Framework
 Database First
 Code First
 MVC Scaffolding

5.  Version 4 released with .NET 4.0
 New version (4.3) allows for model-first, code-first
or database-first development
 Maps POCO objects to database objects
 A collection of things instead of a dataset of rows
 “things” are the entities

6.  Why?
◦ Adds a layer of abstraction between database and
code
◦ DBA can structure database how they want
◦ Developer can map to the database how they want
◦ Rename entities for more comfortable use
◦ Entity Framework handles the mappings

7.  Entity Data Model – EDM
◦ Deals with the entities and relationships they use
 Entities
◦ Instance of EntityType
 Specification for a data type which includes a key and
named set of properties
◦ Represent individual instances of the objects
◦ Customer, book, shoe, usergroup
◦ Fully typed
 Relationships between look up tables are mapped
as associations in the EDMX

8.  csdl
◦ Conceptual Schema Definition Language
◦ The conceputal schema for the EDM
◦ EntityContainer, EntitySet, EntityType definitions
 ssdl
◦ Store Schema Definition Language
◦ Schematic representation of the data store
 msl
◦ Mapping Specification Language
◦ Sits between the csdl and ssdl and maps the entity
properties

9. Lazy Loading
A design pattern to defer initialization until needed
context.ContextOptions.DeferredLoadingEnabled=true;
List<Member> members = context.Members.ToList();
foreach(var member in members)
{
var memberBooks = member.Books;
}

10. Eager Loading
Use if you will be needing every related entity
List<Member> Members =
context.Members.Include(“Books”).ToList();
foreach(var member in members)
{
var memberBooks = member.Books;
}

11. Contexts
 The context is the instance of the entity
 Passing an entity around to tiers breaks the context
 Just like the song, make sure the context remains
the same

12. Contexts
public class ModelHelper
{
private static Entities _db;
public static Entities Entities
{
get
{
if(_db == null)
_db = new Entities();
return _db;
}
set { _db = value; }
}
}
private readonly Entities _db = new Entities();

13. Contexts
private Member AddMember(Member member, UserGroup group)
{
member.UserGroups.Add(group);
_db.SaveChanges();
}
Doesn’t work because group is in a different context
private Member AddMember(Member member, UserGroup group)
{
var newMember = GetMember(member.Id);
var newGroup = GetUserGroup(group.Id);
newMember.UserGroups.Add(newGroup);
_db.SaveChanges();
}

14. LINQ to Entities
Very similar to LINQ to SQL
Selecting
Member member = _db.Members.Single(x=>x.Id == id);
Deleting
public void DeleteMember(Member member)
{
_db.DeleteObject(member);
_db.SaveChanges();
}

15. LINQ to Entities
Adding (Inserting)
public void AddMember(Member member)
{
_db.AddToMembers(member) //this will be a list
_db.SaveChanges() // of AddTo<Entities>
}
Editing (Updating)
public void EditMember(Member member)
{
_db.Members.Attach(new Member{Id=member.Id});
_db.Members.ApplyCurrentValues(member);
_db.SaveChanges();
}

16. Repositories
 Repository pattern encapsulates code into a separate class
 Allows for easy changes
 Can use it to switch database providers or new technologies
 Stephen Walther – ASP.NET MVC Framework, Sams
◦ stephenwalther.com
◦ “Download the code” link
 Add the two projects to your solution
 Add references to your project

17. Repositories
using GenericRepository
public class MyController
{
private readonly IGenericRepository _repo;
private readonly Entities _db;
public MyController()
{
_repo = new
EFGenericRepository.EFGenericRepository(_db);
}
}

18. Repositories
_repo.Get<Member>(id); // get
_repo.Edit(member); // edit
_repo.Create(member); // create
_repo.Delete(member); // delete
// list
var list = _repo.List<Member>().Where(x =>
x.Name.Contains(myName));

19. Database First
 Create the database first
 Build tables and relationships
 Create Entity Data Model (EDMX) in Visual Studio
 Look up tables are converted to Associations

20. Database First

21. Database First
Members_Books UserGroups_Members
Associations representing look up tables

22. Demo

23. Code First – The “Magic Unicorn”
 Write code without having to define mappings in XML
 Define objects in POCO
 No base classes required
 Enables database persistence with no configuration
 Can use Data Annotations
◦ Key
◦ StringLength
◦ Required
◦ RelatedTo
◦ Etc.
 DbContext
◦ Primary object to interact with a database using specific model
 DbSet<TEntity>
◦ Used to perform CRUD against a specific type from the model

24. Code First
 Create classes
 Create Context
 Create Controller
 Write code for
◦ Select
◦ Add
◦ Update
◦ Delete
 Create Views

25. Databases
 By default, creates SQL Express DB
◦ <Project>.Models.<Project>Context.mdf
 Can switch to SQL Compact
1. NuGet
2. Search for SqlServerCompact
3. Install
Adds System.Data.SqlServerCe to references

26. Databases
 Add connection string settings to web.config
 Name needs to match context
<add name=“UserGroups”
connectionString=“Data Source=|DataDirectory|UserGroups.sdf”
providerName=“System.Data.SqlServerCe.4.0” />

27. Databases
 Run the project
 UserGroups.sdf will be created

28. Databases – Keeping Current
 Modifying the database
 Add setting to Global.asax
 Implementation of IDatabaseInitializer
 Deletes and recreates the database

29. Databases – Keeping Current
 EF 4.3.1 uses Code First Migrations
◦ Enabled by default
◦ Adds table __MigrationHistory to database
 Only modifies database if model has changed

30. Demo

31. Scaffolding
 Create MVC project
 Use NuGet to update EntityFramework
 Package Manager Console “Install-Package MvcScaffolding”

32. Scaffolding
 Add Class(es)
 Build Project

33. Scaffolding
 Package Manager Console
 “Scaffold Controller <ClassName>

34. Scaffolding
 Controller and Views are created

35. Scaffolding – Other Commands
 -ControllerName
◦ UserGroupsController – look for class “UserGroup”
◦ UserGroup – creates UserGroupsController
 -ModelType
◦ Inferred from controller name
◦ Can change name of the model if needed
 -Project
◦ Specify the name of the project in multi-project solutions
 -CodeLanguage
◦ Specify “cs” or “vb”
 -DbContextType
◦ Specify the name of the context

36. Scaffolding – Other Commands
 -Repository
◦ Switch. Will generate a repository class for data access
 -Area
◦ For putting the generated files in a specific MVC Area
 -Layout
◦ Which layout page to use if not default _Layout.cshtml
 -Force
◦ Forces overwriting of existing files
 -NoChildItems
◦ Will only generate the controller, no views, repositories or data
contexts

37. Scaffolding
 Add connection string settings to web.config
 Name needs to match context
<add name=“UserGroupsScaffoldingContext”
connectionString=“Data Source=|DataDirectory|UserGroups.sdf”
providerName=“System.Data.SqlServerCe.4.0” />

38. Scaffolding
 Run the project
 Navigate to /UserGroups/
 Database is created

39. Scaffolding
 Scaffold the rest of the classes
 “Scaffold Controller <ClassName>
 Run the project
 Database will be modified with new tables

40. Scaffolding

41. Scaffolding Relationships
 It’s not you, it’s me.
 Add relationships to your classes
Using virtual allows EF to
use Lazy Loading

42. Scaffolding Relationships
 Run the project again
 Database is modified
Look up tables
are created

44.  Slides are at
◦ http://slidesha.re/EFScaffolding
 Inland Empire .NET User’s Group
◦ 2nd Tuesday of each month
◦ www.iedotnetug.org
 james@iedotnetug.org
 @latringo