Data Annotation Basics
suggest changeData annotations are a way of adding more contextual information to classes or members of a class. There are three main categories of annotations:
- Validation Attributes: add validation criteria to data
- Display Attributes: specify how the data should be displayed to the user
- Modelling Attributes: add information on usage and relationship with other classes
Usage
Here is an example where two ValidationAttribute
and one DisplayAttribute
are used:
class Kid
{
[Range(0, 18)] // The age cannot be over 18 and cannot be negative
public int Age { get; set; }
[StringLength(MaximumLength = 50, MinimumLength = 3)] // The name cannot be under 3 chars or more than 50 chars
public string Name { get; set; }
[DataType(DataType.Date)] // The birthday will be displayed as a date only (without the time)
public DateTime Birthday { get; set; }
}
Data annotations are mostly used in frameworks such as ASP.NET. For example, in ASP.NET MVC
, when a model is received by a controller method, ModelState.IsValid()
can be used to tell if the received model respects all its ValidationAttribute
. DisplayAttribute
is also used in ASP.NET MVC
to determine how to display values on a web page.
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