James Johnson is the founder and president of the Inland Empire .NET User's Group. He is a three time Microsoft MVP in CAD and works as a software developer during the day and runs side projects at night. He gave a presentation on Entity Framework and code first development in .NET. He discussed Entity Framework concepts like POCO objects, the entity data model, and LINQ queries. He also covered code first development, scaffolding with MVC, and maintaining databases as the data model changes.

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