Entity Framework Code First and Migrations

Richie Rump@Jorriss

www.jorriss.net

Who is this dude?

What is Entity Framework?

• Object-Relational Mapping Framework• Allows developers to retrieve database

data from an object model.• Converts object data into relational data• Uses your classes• Generates SQL

Before Code First…

EF 4.1 – A New Hope

• Code First Model• DbContext• Fluent API

EF 4.2 – Much Ado About Versioning

• Bug Fixes• Semantic VersioningBecause Entity Framework 4.2 is better than:Entity Framework 4.1 Service Pack 2 Update 1 Refresh Release To Web Pack

EF 4.3 – More Like Hibernate

• Code First Migrations• Data Annotations on non-public properties• Additional configuration file settings• Removal of EdmMetadata table• Bug Fixes

EF 4.3.1 – Oops, I Did It Again

• Added –IgnoreChanges to enable CodeFirst against existing database.

• More inevitable bug fixes.

How it all fits

Entity Framework 4.0included with .Net 4.0

EF 4.1 - Code First & DbContext

EF 4.2 – Bug Fixes

EF 4.3 - Migrations

EF 4.3.1 – Bug Fixes

Entity Framework ModelsDesign First Code First

New Database

Existing Database

Model FirstCreate .edmx model in designerGenerate DB from .edmxClasses auto-generate from .edmx

Database FirstReverse engineer .edmx modelClasses auto-generate from .edmx

Code FirstDefine classes & mapping in codeDatabase auto-created at runtime

Code FirstDefine classes & mapping in code

Adapted from Programming Entity Framework: Code First by Julie Learman and Rowan Miller page 3.

So how does this thing work?

Lovingly stolen from Programming Entity Framework: Code First by Julie Lerman and Rowan Miller page 9.

How do I get this thing?

In a word: Nuget

Code First

• What does code look like?• How do we use it?• Stop! Demo time.

Review

• Convention over configuration– Database naming– Primary Key

• SQL Server Express – default database• dbContext Class

Data Annotations

• It’s not enough to use convention.• Tells EF how to map the object model to the

database model.• Place annotations directly against the property

in your class.• System.ComponentModel.DataAnnotations

Common Data Annotations

• Key – Defines a Primary Key• Column – Defines DB column name• Table – Defines table name for a class• Required – Defines a Required DB field• NotMapped – Property not in DB mapping• MinLength() – Min length for a property• MaximumLength() – Max length for property• Range() – Defines a valid value range

Data Annotation - Example    [Table(“Product_Order")]    public class Order    {        [Key]        [Column("Order_ID")]        public int OrderId { get; set; }         public DateTime Date { get; set; }        public OrderState State { get; set; }        public string Item { get; set; }        [Range(1, 25)]        public int Quantity { get; set; }        [MinLength(3, ErrorMessage="What are you thinking?")]        [MaxLength(50, ErrorMessage="ERROR!! FAILZ!!!!")]        public string Name { get; set; }        [NotMapped]        public string Note { get; set; }    }

Fluent API

• Allows you to configure EF without polluting your classes with annotations.

• Cleaner code• Can have all EF mapping code in one file.• Some things you can only do in the Fluent API

A Comparison

Data Annotations

Fluent APImodelBuilder.Entity<Order>() .Property(p => p.Id).HasColumnName("Order_ID");

[Column("Order_ID")]public int Id { get; set; }

Demo – Fluent API

• This time it will work…I swear!

Relationships: Everyone wants one

• Expressed via the navigation properties in your classes

public class Order    

{

        public int Id { get; set; }

       public OrderState State { get; set; }

}

Fluent API: M:1

Fluent API: M:1

public OrderConfiguration() { ToTable("Order"); Property(p => p.OrderStateID).HasColumnName("Order_State_ID"); HasRequired(p => p.State).WithMany() .HasForeignKey(f => f.OrderStateID); }

public class Order { public int Id { get; set; } public int OrderStateID { get; set; } public OrderState State { get; set; } }

public class OrderState { public int Id { get; set; } }

Fluent API: M:1 with Navigation

Fluent API: M:1 with Navigation

public OrderConfiguration() { ToTable("Order"); Property(p => p.PersonID).HasColumnName("Person_ID"); HasRequired(p => p.SalesPerson).WithMany(t => t.Orders) .HasForeignKey(f => f.PersonID);}

public class Person { public int PersonID { get; set; } ... public List<Order> Orders { get; set; } }

public class Order { public int Id { get; set; } public int PersonID { get; set; } public virtual Person SalesPerson { get; set; } }

Fluent API: M:N

Fluent API: M:N

HasMany(p => p.Items).WithMany(t => t.Orders) .Map(m =>   { m.ToTable("Order_Item"); m.MapLeftKey("Order_ID"); m.MapRightKey("Item_ID"); });

public class Item { public int Id { get; set; } ... public List<Order> Orders { get; set; } }

public class Order { public int Id { get; set; } ... public List<Item> Items { get; set; } }

DbContext API

• New way to interact with EF objects• Makes interaction with EF MUCH simpler• Encapsulates existing EF objects such as

ObjectContext, ObjectSet and ObjectQuery

DbContext API

• DbContext – Provides facilities querying and persisting object changes.

• DbSet – Represents an entity for CRUD operations

• Change Tracker API and Validation API are other features

Query Examples

EFTestContext context = new EFTestContext();

var query = context.Orders .Where(c => c.PersonID == 22) .Include(c => c.State) .ToList();

List<Order> orders = context.Orders.ToList();

DbContext API

• Easy way to retrieve an object via the Primary Key.

EFTestContext context = new EFTestContext(); Person p = context.People.Find(1);

Add Object

EFTestContext context = new EFTestContext(); Person p = new Person { FirstName = "Testy", LastName = "User" }; context.People.Add(p); context.SaveChanges();

Delete Object

EFTestContext context = new EFTestContext(); Person p = context.People.Find(1); context.People.Remove(p); context.SaveChanges();

Migrations

• Migrations is a new way to generate database changes automatically

• It’s controlled through PowerShell commands• Can migrate forward or rollback DB changes.• Migrations can be handled automatically. EF

will automatically apply change scripts

Enable Migrations

• To turn Migrations on

• This creates a Migration folder in project• Creates Configuration.cs file• Creates __MigrationHistory system table in DB

PM> Enable-Migrations

Add Migration

• “Initial” is the name of the migration• The –IgnoreChanges switch tells EF to create an

empty migration. Use this if this is the first migration and EF did not create the DB.

• Creates a cs file with the changes since the last migration.

• Does not apply changes to DB.

PM> Add-Migration "Inital" -IgnoreChanges

Update Database

• Pushes the migration changes to the DB• Use the –script switch to have EF create a SQL

script of the changes. • Use –TargetMigration to determine end point for

DB. (Rollback/Forward)• Be careful. I wouldn’t run against a production

DB.

PM> Update-Database

Y U NO DO DATABASE RIGHT?!?!?!!!

What’s Next? EF 5.0

• Now in Release Candidate• Install using Nuget

Install-Package EntityFramework –Pre• ENUMS!• Performance Improvements• Spatial Data Types• Table-Valued Functions• Most features only in .Net 4.5

Reference

Other References

• Julie Lerman’s Bloghttp://thedatafarm.com/blog/

• Rowan Miller’s Bloghttp://romiller.com

• Arthur Vicker’s Bloghttp://blog.oneunicorn.com

• #efhelp on twitter• StackOverflow (of course)• PluralSight – Julie Lerman’s EF videos

Thank You!!

Richie Rump@Jorrisshttp://jorriss.nethttp://dotnetmiami.com