A foreign key is a column or set of columns whose values reference a key in another table. In EF Core, Rating.BookId references Book.Id, linking each dependent Rating to its principal Book. section 5.2.3
Use foreign keys to model these relationship patterns:
- One-to-one: a Book can optionally have one Rating; EF Core does not automatically enforce database-level uniqueness for this relationship. section 5.2.3
- One-to-many: a Book has a collection of Ratings, with each Rating carrying BookId. section 5.2.3
- Many-to-many: EF Core uses a join table because one foreign-key column cannot represent both directions. section 5.2.3
Listing 5.8 One-to-one relationship with Book as the parent and Rating as the child
class Book {
public int Id {get;set;}
public Rating? Rating {get;}
}
class Rating
{
public int Id {get;set;}
public int BookId {get;set;}
public Book Book {get;set}
}
The C# model shows the foreign-key property beside navigation properties, allowing EF Core conventions to establish the relationship. section 5.2.3
