question for ADO.NET chapter 14

stram · September 26th, 2010, 03:17 PM

hello all. i have a question that is confusing me. On page 482 the book writes that the tables(Genre and review) on figure 14.2 named classes...But on How it works on page 484 on second paragraph i read "objects". does it referring to the previous thing?(classes) ? does it the same as oo programming where we have objects that created by classes?

also i want to know where is used the navigation properties below the classes.

thanks

Imar · September 27th, 2010, 02:26 AM

Quote:

does it the same as oo programming where we have objects that created by classes?

Yes, it's the same. Based on the database, Visual Studio generates classes for you. The LINQ to SQL run time then creates objects based on these class definitions.

Quote:

also i want to know where is used the navigation properties below the classes.

This makes no sense to me, so I am afraid I can't answer it.

Cheers,

Imar

stram · September 27th, 2010, 04:34 AM

hello Imar. thanks for the first answer.

for the second question:

i can't understand what is navigation properties? for example genre has navigation properties Reviews. did it created when I create the relationship between two tables?

Imar · September 27th, 2010, 04:51 AM

Hi stram,

It doesn't do that when you create the relationship in the database, but when you create the model in Visual Studio. When you create the model, Visual Studio analyses your database and detects the relationship. It then creates a Navigation property in both classes; one a single instance, the other a collection (so you can navigate from a genre to its reviews - myGenre.Reviews - and back - myReview.Genre).

Hope this helps,

Imar

stram · September 27th, 2010, 05:28 AM

Quote:

Originally Posted by Imar

(so you can navigate from a genre to its reviews - myGenre.Reviews - and back - myReview.Genre).

can you give me an example where it used? or an example in the book?
thanks

Imar · September 27th, 2010, 06:00 AM

One place where it's used is in the Code Behind of AllByGenre.aspx:

Code:

     Dim allGenres = From genre In myEntities.Genres
                      Order By genre.Name
                      Select New With {genre.Name, genre.Reviews}

Code:

 
      var allGenres = from genre in myEntities.Genres
                      orderby genre.Name
                      select new { genre.Name, genre.Reviews };

Cheers,

Imar

stram · September 27th, 2010, 06:44 AM

ok Imar I understand it.

thanks