/// <summary>
/// Updates the Genre in the Genres collection.
/// </summary>
/// <param name="UnitOfWork">The In-Memory context</param>
/// <param name="Genre">The Genre to be updated</param>
/// <param name="Album">The album</param>
/// <returns>The Updated Genre</returns>
/// <remarks>
/// <para>
/// The update genre is returned so that it can replace the
/// genre in the album, which means the navigation properties
/// are up to date.
/// </para>
/// <para>
/// Only add an AlbumId if to the AlbumIds collection if it's not already there.
/// It won't be if the its is a New Album being created, but there will be when
/// reloading the persisted data.
/// </para>
/// <para>
/// Concurrency:
/// </para>
/// <Para>
/// This routine provides a Monitor lock to ensure that only one instance of this
/// can modify the Genres collection at a time.
/// It locks from the point where the Genre to be updated is retrieved from
/// the Genres
/// and retains that until the Genre is updated in the Genres collection.
/// This type of lock is preferred to ensure that no other updates to the Genres
/// is attempted while this update occurs.
/// </Para>
/// <para>
/// This is a very course grained way of locking but is acceptible within this
/// application as it is a Windows 8 store app, and not subjected to multiple
/// users, only the individual threads within the application. The performance
/// hit should not be that noticable here.
/// </para>
/// </remarks>
private Genre UpdateGenre(IUnitOfWork UnitOfWork, Genre Genre, Album Album)
{
// TODO: Refactor this to use the concurrent collection.
var idx = 0;
lock (_GenreLock)
{
// Get the index of the Genre
idx = UnitOfWork.Genres.FindIndex(g => g.Name == Genre.Name);
// Get the Genre
var updatedGenre = UnitOfWork.Genres[idx];
// If Album exists in the retrieved Genre.
var al = updatedGenre.Albums.FirstOrDefault(a => a.Id == Album.Id);
if (al != null)
{
// The Album is found, so replace it
var alIdx = updatedGenre.Albums.IndexOf(al);
updatedGenre.Albums[alIdx] = Album;
}
else
{
// Track dosn't exist in the Genres.Tracks collection, so just add it.
AddAlbumToGenre(updatedGenre, Album);
}
// Replace the Genre in the Genres collection
UnitOfWork.Genres[idx] = updatedGenre;
}
// return the updated Genre
return UnitOfWork.Genres[idx];
}
/// <summary>
/// Adds the Album and, if necessary, the Album Id to the Genre
/// </summary>
/// <param name="Genre">The Genre being updated</param>
/// <param name="Album">The album updating the Genre</param>
/// <remarks>
/// <para>
/// Only add an AlbumId if to the AlbumIds collection if it's not already there.
/// It won't be if the its is a New Album being created, but there will be when
/// reloading the persisted data.
/// </para>
/// <para>
/// Concurrency
/// </para>
/// <para>
/// This method doesn't need to be locked as it can only be called from either
/// AddGenre or Updategenre methods, and these are both locking.
/// </para>
/// </remarks>
private void AddAlbumToGenre(Genre Genre, Album Album)
{
// Add the Album to the albums collection
Genre.Albums.Add(Album);
// Only add an AlbumId if to the AlbumIds collection if it's not already there.
// It won't be if the its is a New Album being created,
// but there will be when reloading the persisted data.
if (!Genre.AlbumIds.Contains(Album.Id))
Genre.AlbumIds.Add(Album.Id);
}
/// <summary>
/// Adds a new Genre to the Genres collection of the Domain model. It
/// returns an instance of the Genre added so that it can be used elsewhere.
/// This is standard coding for creating a new object.
/// </summary>
/// <param name="UnitOfWork">The In-Memory context</param>
/// <param name="Genre">the new Genre</param>
/// <param name="Album">The album the Genre relates to</param>
/// <returns>The updated instance of the new Genre</returns>
/// <remarks>
/// Only add an AlbumId if to the AlbumIds collection if it's not already there.
/// It won't be if the its is a New Album being created, but there will be when
/// reloading the persisted data.
/// <para>
/// Concurrency:
/// </para>
/// <Para>
/// This routine provides a Monitor lock to ensure that only one instance of this
/// can modify the Genres collection at a time.
/// It locks from the point which a new Id is generated for the Genre being added
/// and retains that until the Genre is added to the Genres collection.
/// This type of lock is preferred to ensure the generated Id is updated within
/// the Genres collection before any other thread can try and Add a Genre which
/// would require the Id for this one, which woudl be used in the GenerateId
/// methods. This is to avoid duplicate Id's being generated.
/// </Para>
/// <para>
/// This is a very course grained way of locking but is acceptible within this
/// application as it is a Windows 8 store app, and not subjected to multiple
/// users, only the individual threads within the application. The performance
/// hit should not be that noticable here.
/// </para>
/// </remarks>
private Genre AddGenre(IUnitOfWork UnitOfWork, Genre Genre, Album Album)
{
lock (_GenreLock)
{
Genre.Albums = new List<Album>();
// Concurrency: Lock between getting the Id and performing the update, as the
// this new Id won't be availble for checking purposes by another
// thread that is looking to add a Genre. This should avoid the
// possiblilties of duplicate Id's
// i. Generate GenreId, if there isn't one, will be if reloading persisted data.
if (Genre.Id == 0)
Genre.Id = GenerateGenreId(UnitOfWork);
// ii. Add album ref to Genre
AddAlbumToGenre(Genre, Album);
// iii.Add Genre to Genres Collection
UnitOfWork.Genres.Add(Genre);
}
return Genre;
}
