Looping through objects in model odoo 11

Question

I'd like to create a function on my model 'Artist' to change the field num_albums to the number of albums he created. I imagine that I must use a compute function and filter all of the albums based on the name of the artist. However, I have no idea of how to do it. Please help me if you know how I could do it.

Here's my code:

class Artist(models.Model) :
    _name = 'artist'
    _order = 'name'

    name = fields.Char('Name of Artist')
    age = fields.Integer(string='Age of Artist')
    nationality = fields.Selection([('France', 'France'), ('GB', 'Great Britain'),
    ('USA', 'United States'), ('Russia', 'Russia'), ('China', 'China'),
    ('Other', 'Other')], 'Nationality')
    num_albums = fields.Integer(compute='_get_num_albums', store=False)

    @api.model
    def _get_num_albums(self) :
        **Enter code here**

class Album(models.Model) :
    _name = 'album'
    _order = 'artist.name'

    artist = fields.Many2one('artist', string='Artist')
    name = fields.Char('Name')
    image = fields.Binary('Album Cover')

Answer 1

You could declare a One2many relation from artist to his/her albums and then simply use the number of albums, eg.:

class Artist(models.Model):
    _name = 'artist'
    _order = 'name'

    # ...
    albums = fields.One2many(
        comodel_name='album',
        inverse_name='artist',
        string='Albums',
    )
    num_albums = fields.Integer(compute='_get_num_albums', store=False)

    @api.multi
    def _get_num_albums(self):
        for artist in self:
            artist.num_albums = len(artist.albums)

    # ...

Or, without adding additional fields, you could use search_count to get the number of albums by an artist:

class Artist(models.Model):
    _name = 'artist'
    _order = 'name'

    # ...
    num_albums = fields.Integer(compute='_get_num_albums', store=False)

    @api.multi
    def _get_num_albums(self):
        album_obj = self.env['album']
        for artist in self:
            artist.num_albums = album_obj.search_count([
                ('artist', '=', artist.id),
            ])
    # ...