implemented two views for meta information, added basic trigger code with cursor

Author: danielkleebinder

CreateViews.sql

@@ -0,0 +1,38 @@
+USE [Music];
+GO
+
+
+----------------------------------------------------------------------
+-- a view which stores the number of genres in a playlist as key    --
+-- value pairs.                                                     --
+----------------------------------------------------------------------
+IF OBJECT_ID('VW_NumberOfGenresInPlaylist', 'V') IS NOT NULL
+	DROP VIEW [VW_NumberOfGenresInPlaylist];
+GO
+
+CREATE VIEW [VW_NumberOfGenresInPlaylist]
+AS
+	SELECT	pt.[fk_playlist_id] AS "playlist_id",
+			Count(DISTINCT t.[fk_genre_id]) As "Number of Genres"
+	FROM [playlist_title] AS pt
+	INNER JOIN [title] AS t ON t.[title_id] = pt.[fk_title_id]
+	GROUP BY pt.[fk_playlist_id];
+GO
+
+
+----------------------------------------------------------------------
+-- a view which stores the number of interprets per album as key    --
+-- value pairs.                                                     --
+----------------------------------------------------------------------
+IF OBJECT_ID('VW_NumberOfInterpretsInAlbum', 'V') IS NOT NULL
+	DROP VIEW [VW_NumberOfInterpretsInAlbum];
+GO
+
+CREATE VIEW [VW_NumberOfInterpretsInAlbum]
+AS
+	SELECT	t.[fk_album_id] AS "album_id",
+			Count(DISTINCT ti.[fk_interpret_id]) As "Number of Interprets"
+	FROM [title] AS t
+	INNER JOIN [title_interpret] AS ti ON ti.fk_title_id = t.title_id
+	GROUP BY t.[fk_album_id];
+GO

Triggers/TR_Template.sql

@@ -0,0 +1,27 @@
+USE [Music];
+GO
+
+
+------------------------------------------------------------------------------
+-- checks if the trigger already exists using the sys.objects and drops it. --
+------------------------------------------------------------------------------
+IF EXISTS (SELECT * FROM sys.objects WHERE [name] = N'TR_' AND [type] = 'TR')
+	DROP TRIGGER [TR_]
+GO
+
+
+------------------------------------------------------------------------------
+--
+------------------------------------------------------------------------------
+CREATE TRIGGER [TR_] ON ___table___
+INSTEAD OF INSERT								-- SQL Server does not support BEFORE triggers
+AS BEGIN
+	-- trigger code goes here
+END
+GO
+
+
+------------------------------------------------------------------------------
+-- test code for checking trigger behavior.                                 --
+------------------------------------------------------------------------------
+

Triggers/TR_UniqueTitleNumberInAlbum.sql

@@ -0,0 +1,99 @@
+USE [Music];
+GO
+
+
+------------------------------------------------------------------------------
+-- checks if the trigger already exists using the sys.objects and drops it. --
+------------------------------------------------------------------------------
+IF EXISTS (SELECT * FROM sys.objects WHERE [name] = N'TR_UniqueTitleNumberInAlbum' AND [type] = 'TR')
+	DROP TRIGGER [TR_UniqueTitleNumberInAlbum];
+GO
+
+
+------------------------------------------------------------------------------
+--
+------------------------------------------------------------------------------
+CREATE TRIGGER [TR_UniqueTitleNumberInAlbum] ON [title]
+INSTEAD OF INSERT				-- SQL Server does not support BEFORE triggers
+AS BEGIN
+	DECLARE @TitleNumber SMALLINT,
+			@TitleAlbum	INT;
+
+	DECLARE CUR_InsertedTitle CURSOR FORWARD_ONLY FOR
+		SELECT ins.[titlenumber], ins.[fk_album_id]
+		FROM [inserted] AS ins;
+
+	BEGIN TRANSACTION;
+		OPEN CUR_InsertedTitle;
+		FETCH NEXT FROM CUR_InsertedTitle INTO @TitleNumber, @TitleAlbum;
+
+		WHILE @@FETCH_STATUS = 0 BEGIN;
+			IF ((SELECT Count(*) FROM [title] AS t
+					WHERE t.[titlenumber] = @TitleNumber
+					AND t.[fk_album_id] = @TitleAlbum) > 0)
+			BEGIN;
+				ROLLBACK;
+				
+				-- close cursor and free allocated memory to prevent memory leaks
+				CLOSE CUR_InsertedTitle;
+				DEALLOCATE CUR_InsertedTitle;
+
+				THROW 47000, 'Titlenumber already exists in this album', 2;
+			END;
+
+			BEGIN TRY;
+				INSERT INTO
+					[title] ([name], [titlenumber], [duration], [bitrate], [fk_genre_id], [fk_album_id])
+					VALUES ();
+			END TRY BEGIN CATCH;
+				ROLLBACK;
+
+				-- close cursor and free allocated memory to prevent memory leaks
+				CLOSE CUR_InsertedTitle;
+				DEALLOCATE CUR_InsertedTitle;
+
+				RETURN 1;
+			END CATCH;
+			
+			FETCH NEXT FROM CUR_InsertedTitle INTO @TitleNumber, @TitleAlbum;
+		END;
+	ROLLBACK;
+
+	-- close cursor and free allocated memory to prevent memory leaks
+	CLOSE CUR_InsertedTitle;
+	DEALLOCATE CUR_InsertedTitle;
+
+	/*
+	DECLARE CUR_AlbumTitle CURSOR FORWARD_ONLY FOR
+		SELECT t.[titlenumber] FROM [title] AS t
+		INNER JOIN [inserted] AS ins ON ins.fk_album_id = t.fk_album_id;
+
+	BEGIN TRANSACTION;
+		OPEN CUR_AlbumTitle;
+		FETCH NEXT FROM CUR_AlbumTitle INTO @TitleNumber;
+
+		WHILE @@FETCH_STATUS = 0 BEGIN;
+			IF (@TitleNumber = ANY(SELECT [titlenumber] FROM [inserted])) BEGIN;
+				ROLLBACK;
+				THROW 47000, 'Titlenumber already exists in this album', 2;
+			END;
+
+			FETCH NEXT FROM CUR_AlbumTitle INTO @TitleNumber;
+		END;
+	ROLLBACK;*/
+
+	-- close cursor and free allocated memory to prevent memory leaks
+	CLOSE CUR_AlbumTitle;
+	DEALLOCATE CUR_AlbumTitle;
+END
+GO
+
+
+------------------------------------------------------------------------------
+-- test code for checking trigger behavior.                                 --
+------------------------------------------------------------------------------
+INSERT INTO [album] ([name], [releaseyear]) VALUES ('Album #1', 2017);
+INSERT INTO [title] ([name], [titlenumber], [duration], [bitrate], [fk_genre_id], [fk_album_id]) VALUES ('Title #1', 1, 300, 20000, 1, 1);
+INSERT INTO [title] ([name], [titlenumber], [duration], [bitrate], [fk_genre_id], [fk_album_id]) VALUES ('Title #2', 1, 400, 30000, 1, 1);
+
+SELECT * FROM [title];