02 beginning code first

1. 02 | Beginning Code First
Adam Tuliper | Technical Evangelist
Christopher Harrison | Content Developer

2. • Simple Code First
• Creating classes
• Creating Data Context
• Initializing the database
Code First

3. Simple Code First

4. public class Artist
{
public int ArtistID { get; set; }
public string Name { get; set; }
public string Bio { get; set; }
}

5. Code first classes…
are just classes

6. Code first class design tips
• Just design your classes the way you typically would
– (for the most part)
• Use standard conventions
– ID for the ID
• You can still control the database
– Attributes
– Fluent API

7. Creating classes

8. But what about my database?
• Code First often does the right thing
• But it does need a little guidance
• For example, strings become nvarchar(max)

9. Basic database control
• Data annotations can be used to provide additional context
– System.ComponentModel.DataAnnotations
– https://msdn.microsoft.com/en-
us/library/system.componentmodel.dataannotations(v=vs.110).aspx
• Not specific to Entity Framework
– Used by several other platforms, including MVC

10. Code First conventions
• Tables are automatically pluralized
• Tables are created in the dbo schema
• ID property is created as the primary key
– Identity or auto-count column

11. Table creation
• TableAttribute
– Schema
– Name
• ColumnAttribute
– Name

12. Strings
• Nullable nvarchar(max) is the default
• Attributes
– StringLengthAttribute
• MaximumLength
• MinimumLength
– RequiredAttribute

13. Numbers
• SQL data type is mapped to .NET data type
– long becomes BigInt
• RangeAttribute
– Maximum
– Minimum

14. Value types and nullability
• Dates and numbers are value types in .NET
• Value type properties must be marked as nullable
– Nullable<T>
– type?

15. DEMO
Attributes and database control
(warning... This demo is going to fail. Well, sort of.)

16. Creating the Data Context

17. Creating the Data Context
• Just like creating a normal class
– It's like it's called Code First 
public class MusicStoreDbContext : DbContext
{
public DbSet<Artist> Artists { get; set; }
}

18. DEMO
Creating the DbContext

19. The Find() method
• Regardless of the data type you're going to need to look the
object up by its key
• Rewriting that code over and over again becomes tedious
• The Find method will do that for you
• Accepts a parameter that maps to the key
• Returns the object if it's found
• Returns null if it isn't

20. DEMO
Creating a repository

21. Initializing the database

22. Testing requires a known starting state
• Entity Framework provides database initializers to create that
state
• Create a class that inherits from the appropriate option
– CreateDatabaseIfNotExists
– DropCreateDatabaseWhenModelChanges
– DropCreateDatabaseAlways
• Override the Seed method to create database content
• Register the method with Database.SetInitializer

23. DEMO
Initializing the database

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