Entity Framework Database and Code First
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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 where he demonstrated how to scaffold controllers and views from classes to generate a basic web application with CRUD functionality and database access.
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Entity Framework Database and Code First
- 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 [email protected] @latringo