Entity Framework ForeignKey Data Annotations

The ForeignKey attribute is used to specify which property is the foreign key in a relationship. It is used to express the relationship between two tables.

• The default code first convention for ForeignKey relationship expects foreign key property name match with the primary key property.
• If your code is not using the default code first conventions, then you can use ForeignKey attribute, so that code first can identify that it contains the foreign key.

In the following example, the AuthorBiographyId property in the AuthorBiography entity does not follow the Entity Framework convention for foreign key names, and it will create an AuthorId field which it will configure as a foreign key.

public class Author
{
    public int AuthorId { get; set; }
    public string Name { get; set; }
}

public class AuthorBiography
{
    public int AuthorBiographyId { get; set; }
    public string Biography { get; set; }
    public DateTime DateOfBirth { get; set; }
    public string PlaceOfBirth { get; set; }
    public string Nationality { get; set; }
    public virtual Author Author { get; set; }
}

The ForeignKey attribute can be used to configure the relationship correctly, and prevent the generation of an AuthorId column in the AuthorBiography table.

public class Author
{
    public int AuthorId { get; set; }
    public string Name { get; set; }
}

public class AuthorBiography
{
    [ForeignKey("Author")]
    public int AuthorBiographyId { get; set; }
    public string Biography { get; set; }
    public DateTime DateOfBirth { get; set; }
    public string PlaceOfBirth { get; set; }
    public string Nationality { get; set; }
    public virtual Author Author { get; set; }
}

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