Building a Photo Tagging Application using ASP.NET 2.0, LINQ, and Atlas
page 4 of 9
by Scott Guthrie
Feedback
Average Rating: This article has not yet been rated.
Views (Total / Last 10 Days): 41020/ 100

Step 3: Using LINQ to work with data and Tag Photos in our application

LINQ makes working with data a real joy.  It automatically handles relationships, hierarchy, and tracking changes within our model – eliminating tons of data access code. 

For example, to create a new album and a photo within it, I could extend our previous code-sample like this:

Listing 3

PhotoDB photoDb = new PhotoDB();
Photographer photographer1 = new Photographer();
photographer1.PhotographerName = "Scott Guthrie";
Photo photo1 = new Photo();
photo1.Description = "Picture of Lion";
photo1.Url = "http://someurl";
photo1.Thumbnail = "http://thumbnailurl";
photo1.Photographer = photographer1;
Album album1 = new Album();
album1.AlbumName = "Africa Trip";
album1.Photos.Add(photo1);
photoDb.Albums.Add(album1);
photoDb.SubmitChanges();

This is all of the code needed to add a new Photographer, Photo and Album into the database, setup the FK relationship between the Photographer and Photo, and setup the Photo and the Album FK relationship (notice how this relationship is expressed by adding the photo into the Album’s photo collection, and by setting the Photographer property on Photo).  Because these properties and collections are strongly-typed, we get full compile-time checking and intellisense of our syntax and data relationships.

C# has also added new syntax support that can be used to make object initialization even terser/cleaner than what I did above.  Specifically, it now allows developers to declare properties (and collections) using syntax like below if you prefer:

Listing 4

PhotoDB photoDb = new PhotoDB();
 
Photographer scott = new Photographer()
{
  PhotographerName = "Scott Guthrie"
};
 
photoDb.Albums.Add(new Album()
{
  AlbumName = "South Africa", Photos =
  {
    new Photo()
    {
      Description = "Lion Close Up", Photographer = scott, Url = "http://url1",
        Thumbnail = "http://thumb1",
    }
    , new Photo()
    {
      Description = "Zebras at Dusk", Photographer = scott, Url =
        " http://url2", Thumbnail = " http://thumb2",
    }
  }
}
 
);
 
photoDb.SubmitChanges();

This is syntactically equivalent to the code before – except that we are now able to compact more functionality in fewer lines of code.  In the example above, I’m now adding two new photos to the new South Africa album (with me as the photographer for both pictures).

Because we setup FK relationships between the Photo table and the Tags table, we get automatic association linking between them with LINQ (this is expressed via the “Tags” property on Photos and the corresponding “Photo” property on each Tag).  For example, I could use the below code to fetch one of our newly created Photo’s above from the database and associate three new Tags to it:

Listing 5

PhotoDB photoDB = new PhotoDB();
Photo photo = photoDB.Photos.Single(p =  > p.Description == "Lion Close Up");
photo.Tags.Add(new Tag()
{
  Name = "Lion"
}
 
);
photo.Tags.Add(new Tag()
{
  Name = "AndersH"
}
 
);
photo.Tags.Add(new Tag()
{
  Name = "ScottGu"
}
 
);
 
photoDb.SubmitChanges();
 

I could then use the below code to retrieve a Photo and output its tags within a page:

 
PhotoDB photoDB = new PhotoDB();
 
Photo photo = photoDB.Photos.Single(p =  > p.Description == "Lion Close Up");
 
foreach (Tag tag in photo.Tags)
{
  Response.Write("Tag : " + tag.Name);
}        

I could also then write this code to easily retrieve all Photos that are tagged with a specific tag-name, and output the Photo description and photographer name for each of them:

Listing 6

PhotoDB photoDb = new PhotoDB();
string tagName = "Lion";
var photos = from photo in photoDb.Photos where photo.Tags.Any(t =  > t.Name ==
  tagName)select photo;
foreach (Photo photo in photos)
{
  Response.Write("Photo: " + photo.Description + " by: " +
    photo.Photographer.PhotographerName);
}        

I do not need to write any extra data code to make the above code work.  LINQ handles all of the SQL statement execution for me.  This provides an incredibly flexible and elegant way to perform data access.


View Entire Article

User Comments

Title: dfds   
Name: vvxc
Date: 2012-11-02 8:00:17 AM
Comment:
vxcv
Title: Dear   
Name: Bilal khan
Date: 2012-08-07 1:13:37 PM
Comment:
Plz send this article to my email address


iam.bilal@yahoo.com

thanks in advance
Title: th   
Name: Janaa
Date: 2009-09-28 9:09:50 AM
Comment:
Thats seems to be very useful. I will try to use it on my site thx.






Community Advice: ASP | SQL | XML | Regular Expressions | Windows


©Copyright 1998-2019 ASPAlliance.com  |  Page Processed at 2019-09-15 10:32:47 PM  AspAlliance Recent Articles RSS Feed
About ASPAlliance | Newsgroups | Advertise | Authors | Email Lists | Feedback | Link To Us | Privacy | Search