Basic Annotations

[Table("Passport")]
public class Passport
{
	[Key]
	[DatabaseGenerated(DatabaseGenerationOption.Identity)]
	[Column(Order=1)]
	public int PassportNumber { get; set; }

	[Key]
	[Column(Order = 2)]
	[Column("IssuingCountry", TypeName="NVARCHAR")]
	public string IssuingCountry { get; set; }

	[Required]
	public DateTime Issued { get; set; }
	public DateTime Expires { get; set; }
}

public class PassportStamp
{
	[Key]
	[DatabaseGenerated(DatabaseGenerationOption.Computed)]
	public int StampId { get; set; }

	public DateTime Stamped { get; set; }

	[MaxLength(10), MinLength(5)]
	public string StampingCountry { get; set; }

	[ForeignKey("Passport")]
	[Column(Order = 1)]
	public int PassportNumber { get; set; }

	[ForeignKey("Passport")]
	[Column(Order = 2)]
	public string IssuingCountry { get; set; }

	public Passport Passport { get; set; }
	
	[InverseProperty("CreatedBy")]
  public List<Post> PostsWritten { get; set; }

	[NotMapped]
  public string Code => IssuingCountry.Substring(0, 1) + ":" + PassportNumber;
}

Complex Types

• It’s not uncommon to describe a domain entities across a set of classes and then layer those classes to describe a complete entity.
  • For example, you may add a class called BlogDetails to describe Blog entity.
  • In domain driven design, BlogDetails is referred to as a value object.
  • Now you can add a property to the Blog class to represent the BlogDetails for that blog.
• Entity Framework refers to value objects as complex types.
• Complex types cannot be tracked on their own.

[ComplexType]
public class BlogDetails
{
	public DateTime? DateCreated { get; set; }

    [MaxLength(250)]
    public string Description { get; set; }
}

Concurrency Check

• The ConcurrencyCheck annotation allows you to flag one or more properties to be used for concurrency checking in the database when a user edits or deletes an entity.
• When SaveChanges is called, because of the ConcurrencyCheck annotation on the field, the original value of that property will be used in the update.
• The command will attempt to locate the correct row by filtering not only on the key value but also on the original value of entity.
• If someone has changed the field for that entity in the meantime, the update will fail and you’ll get a DbUpdateConcurrencyException that you'll need to handle.

[ConcurrencyCheck, MaxLength(10, ErrorMessage="BloggerName must be 10 characters or less"), MinLength(5)]
public string BloggerName { get; set; }

Time Stamp

• It's more common to use rowversion or timestamp fields for concurrency checking.
• Rather than using the ConcurrencyCheck annotation, you can use the more specific TimeStamp annotation as long as the type of the property is byte array.
• Code first will treat Timestamp properties the same as ConcurrencyCheck properties, but it will also ensure that the database field that code first generates is non-nullable.
• You can only have one timestamp property in a given class.

[Timestamp]
public Byte[] TimeStamp { get; set; }

Index Attribute