foreignkey column in object relation model in C#
why in ORM(object relation model) Mode开发者_如何学Cl in this sample foreignkey column publisher in book class is a class of publisher,while where we could use of a long type(in database publisher is foreignkey and Bigint)?
public class Publisher
{
[XmlAttribute]
public string Title { get; set; }
[XmlAttribute]
public string Address { get; set; }
}
public class Book
{
[XmlElement]
public Publisher Publisher { get; set; } ******
[XmlAttribute]
public string Title { get; set; }
[XmlAttribute]
public short PrintYear { get; set; }
[XmlAttribute]
public short Pages { get; set; }
[XmlAttribute]
public string ISBN { get; set; }
}
This is to make your life easier. In your database the table BOOK
has a PublisherId
that is a foreign key to the table PUBLISHER
. To avoid the need to write relational joins in your C# code as you need to do in SQL, your Book
class has a property of the referenced type Publisher
, so you can directly access it. This also conforms more to OOD principles.
Example:
If your class Book
only had a public int PublisherId {get;set;}
, you would need the following code to get the publisher's Title
:
Book book = ...
Publisher publisher = context.Publishers
.Where(x => x.PublisherId == book.PublisherId)
.SingleOrDefault();
if(publisher != null)
Console.WriteLine(publisher.Title);
With the current Book
class, this is shorter and easier to read:
Book book = ...
Publisher publisher = book.Publisher;
if(publisher != null)
Console.WriteLine(publisher.Title);
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