关键和必需数据注释

Question

When using the entity framework there are the following data annotations:

• System.ComponentModel.DataAnnotations.KeyAttribute
• System.ComponentModel.DataAnnotations.RequiredAttribute

Just for reference, I using the definitions from this wiki article :

Primary Key

1. A primary key cannot allow null values. (You cannot define a primary key on columns that allow nulls.)
2. Each table can have at most one primary key.

Unique Key

1. A unique key can allow null values. (You can define a unique key on columns that allow nulls.)
2. Each table can have multiple unique keys.

Is the KeyAttribute used to denote a primary key or is it used to denote a unique key?

When using annotations would the following be considered reduntant or necessary?

class Example
{
    [Required(), Key()]
    public int Id { get; set; }
    ...
}

Answer 1

In your example, that would be redundant as your models require a key value to uniquely identify them once they have been annotated with Key .

And as an aside, if you are using Code-First, even Key would be redundant as by convention a property called Id or ModelNameId would be used for your primary key.