- Build custom class constructors.
- Build class finders.
- Build class operators.
This lab has provided you with a base Song
class that provides the following
definition:
class Song
attr_accessor :name, :artist_name
@@all = []
def self.all
@@all
end
def save
self.class.all << self
end
end
The Song
class provides a class variable @@all
to store all instances for
Song
that are created through the instance method Song#save
. Additionally,
Song
instances have basic properties of a name and an artist name.
You have to build class methods that interact on the class data of @@all
and
provide the rest of our program with a semantic API on the Song
class with
methods such as Song.find_or_create_by_name("Blank Space")
.
Build a class constructor Song.create
that initializes a song and saves it to
the @@all
class variable either literally or through the class method
Song.all
. This method should return the song instance that was initialized and
saved.
Consider:
song = Song.create
Song.all.include?(song) #=> true
Build a class constructor Song.new_by_name
that takes in the string name of a
song and returns a song instance with that name set as its name property.
Song.new_by_name
should return an instance of Song
and not a simple string
or anything else. Implement the following functionality:
song = Song.new_by_name("The Middle")
#=> #<Song @name="The Middle">
song.name #=> "The Middle"
Build a class constructor Song.create_by_name
that takes in the string name of
a song and returns a song instance with that name set as its name property and
the song being saved into the @@all
class variable.
Consider:
song = Song.create_by_name("The Middle")
#=> #<Song:0x007fd2a2989ff0 @name="The Middle">
song
#=> #<Song:0x007fd2a2989ff0 @name="The Middle">
Song.all.include?(song)
#=> true
Build a class finder Song.find_by_name
that accepts the string name of a song
and returns the matching instance of the song with that name. Consider:
the_middle = Song.create_by_name("The Middle")
#=> #<Song @name="The Middle">
Song.find_by_name("The Middle")
#<Song @name="The Middle">
In order to prevent duplicate songs being created that actually represent the
same song (based on the song name), we're going to build a
Song.find_or_create_by_name
class method. This method will accept a string
name for a song and either return a matching song instance with that name or
create a new song with the name and return the song instance.
Consider:
song_1 = Song.find_or_create_by_name("Blank Space")
song_2 = Song.find_or_create_by_name("Blank Space")
# song_1 and song_2 are conceptually the same song and should return the same song instance because of `.find_or_create_by_name.`
song_1 == song_2 #=> true
Build a class method Song.alphabetical
that returns all the songs in ascending
(a-z) alphabetical order.
Use Array#sort_by.
Build a class constructor that accepts a filename in the format of " - .mp3", for example, "Taylor Swift - Blank Space.mp3".
Given Song.new_from_filename("Taylor Swift - Blank Space.mp3")
, the
constructor should return a new Song
instance with the song name set to Blank
Space and the artist_name set to Taylor Swift. The filename input sent to
Song.new_from_filename
in the format of Taylor Swift - Blank Space.mp3
must
be parsed for the relevant components. Separate the artist name from the rest of
the data based on the -
delimiter. Don't forget that when you parse the song
name, you have to remove the '.mp3'
part of the string.
song = Song.new_from_filename("Taylor Swift - Blank Space.mp3")
song.name #=> "Blank Space"
song.artist_name #=> "Taylor Swift"
Build a class constructor that accepts a filename in the format of " - .mp3", for example "Taylor Swift - Blank Space.mp3". The
Song.create_from_filename
class method should not only parse the filename
correctly but should also save the Song instance that was created.
The Song.destroy_all
class method should reset the state of the @@all
class
variable to an empty array thereby deleting all previous song instances.