3.2: Annotations

In this module we'll discuss Data Annotations.

Key Attribute

In Note.cs we added a [key] attribute. This attribute specifies the property that uniquely identifies an entity. In other words, it's the primary key of the corresponding database. To peek ahead, here's what you'll see:

Key Attribute Example

Let's still examine this key:

public class Order
{
    [Key]
    public int NoteId { get; set; }
}

A single user could have multiple notes, or different users could add a note at the same time, so we need some sort of property that returns a unique note number. In other words the primary key will always be a unique number.

Validation Attributes

There are a few attributes we can use to validate our models. The [Required] attribute ensures the user does not enter a null value. The [Range] attribute ensures the user provides a value within the specified range. Attributes such as [MaxLength] limit the amount of characters users can provide.

Here are a few examples of attributes that could be added to a property:

[Required]
[Range(1,5, ErrorMessage="please choose a number between 1 and 5")]
[MaxLength(100, ErrorMessage = "There are too many characters in this field.")]

Display Attribute

Use the [Display] or [Display(Name)] attribute to change the name the user is shown for a property.

Display Attribute Example

[Display(Name = "Note was Created")]