// In terms of API design, this method expects tag names in the form of a string array.
// We shouldn't use TagId because that would only work if the given tag exists in the database.
// But often, in an application with a good user experience, the user should be able to pick a
// tag from a drop-down list, or add one at the same time as adding or editing a video. So,
// we should use tag names to add a new tag to the database. Plus, tag names should be unique,
// so conceptually, they can be treated as primary keys, but we use an int (TagId) for optimization.
public static void AddTagsToVideo(int videoId, params string[] tagNames)
{
using (var context = new VidzyDbContext())
{
var tags = context.Tags.Where(t => tagNames.Contains(t.Name)).ToList();
foreach (var name in tagNames)
{
if (!tags.Any(t => t.Name == name))
{
tags.Add(new Tag {
Name = name
});
}
}
var video = context.Videos.Include(v => v.Tags).FirstOrDefault(v => v.Id == videoId);
if (video != null)
{
foreach (var tag in tags)
{
if (!video.Tags.Any(t => t == tag))
{
video.Tags.Add(tag);
}
}
}
context.SaveChanges();
}
}
public static void RemoveGenre(int genreId, bool enforceDeletingVideo = false)
{
using (var context = new VidzyDbContext())
{
var genre = context.Genres.Include(g => g.Videos).FirstOrDefault(g => g.Id == genreId);
if (genre == null)
{
return;
}
if (genre.Videos.Any())
{
if (enforceDeletingVideo)
{
context.Videos.RemoveRange(genre.Videos);
}
else
{
throw new Exception(String.Format("Genre {0} contains some video, and can not be deleted.", genre.Name));
}
}
context.Genres.Remove(genre);
context.SaveChanges();
}
}
public static void AddVideo(Video video)
{
using (var context = new VidzyDbContext())
{
context.Videos.Add(video);
context.SaveChanges();
}
}
public static void RemoveVideo(int videoId)
{
using (var context = new VidzyDbContext())
{
var video = context.Videos.FirstOrDefault(v => v.Id == videoId);
if (video == null)
{
return;
}
context.Videos.Remove(video);
context.SaveChanges();
}
}
public static void RemoveTagsFromVideo(int videoId, params string[] tagNames)
{
using (var context = new VidzyDbContext())
{
var video = context.Videos.Include(v => v.Tags).Single(v => v.Id == videoId);
foreach (var tagName in tagNames)
{
// I've encapsulated the concept of removing a tag inside the Video class.
// This is the object-oriented way to implement this. The Video class
// should be responsible for adding/removing objects to its Tags collection.
video.RemoveTag(tagName);
}
context.SaveChanges();
}
}
public static void DisplayGenresAndVideosCount()
{
var context = new VidzyDbContext();
var genres = context.Genres
.GroupJoin(context.Videos,
g => g.Id, v => v.GenreId,
(g, v) => new {
GenreName = g.Name,
VideosCount = v.Count()
})
.OrderByDescending(r => r.VideosCount);
foreach (var g in genres)
{
Console.WriteLine("{0} ({1})", g.GenreName, g.VideosCount);
}
}
public static void AddTags(params string[] tagNames)
{
using (var context = new VidzyDbContext())
{
// We load the tags with the given names first, to prevent adding duplicates.
var tags = context.Tags.Where(t => tagNames.Contains(t.Name)).ToList();
foreach (var name in tagNames)
{
if (!tags.Any(t => t.Name == name))
{
context.Tags.Add(new Tag {
Name = name
});
}
}
context.SaveChanges();
}
}
public static void LoadingReferenceEntity()
{
var context = new VidzyDbContext();
//// To enable lazy loading, you need to declare navigation properties
//// as virtual. Look at the Video class.
//var videos = context.Videos.ToList();
//Console.WriteLine();
//Console.WriteLine("LAZY LOADING");
//foreach (var v in videos)
// Console.WriteLine("{0} ({1})", v.Name, v.Genre.Name);
//// Eager loading
//var videosWithGenres = context.Videos.Include(v => v.Genre).ToList();
//Console.WriteLine();
//Console.WriteLine("EAGER LOADING");
//foreach (var v in videosWithGenres)
// Console.WriteLine("{0} ({1})", v.Name, v.Genre.Name);
// Explicit loading
// NOTE: At this point, genres are already loaded into the context,
// so the following line is not going to make a difference. If you
// want to see expicit loading in action, comment out the eager loading
// part as well as the foreach block in the lazy loading.
// Explicit loading
var videos = context.Videos.ToList();
var genresIds = videos.Select(v => v.GenreId).Distinct();
context.Genres.Where(g => genresIds.Contains(g.Id)).Load();
foreach (var v in videos)
{
Console.WriteLine("{0} [{1}]", v.Name, v.Genre.Name);
}
}