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")]
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