How to return attribute value X - in a Manytomanyfield

Question

I have some classes that relate to each other. Ex: I have an Activity class that has a M2m relationship with an Activity class. And I have another structure class that has a 1to1 with Activities_structures_complementary and with a second class Passive, where I do an inline inclusion in admin. This is my context and below are the respective codes.

Activity:

    class Atividade(models.Model):
        codigoSICRO = models.OneToOneField(Sicro, on_delete=models.CASCADE, unique=True, primary_key=True)
        nome = models.CharField('Nome', max_length=200, unique=True)
        descricao = models.TextField('Descrição', max_length=300, blank=True)
        unidadeMedida = models.ForeignKey(Unidade, on_delete=models.DO_NOTHING)

    def __str__(self):
        return self.nome

List of Activities of Complementary Structures:

    class Atividade_estruturas_complementares(models.Model):
        atividades_complementares = models.ManyToManyField(Atividade)

        class Meta:
            verbose_name_plural = 'Estruturas Complementares'
            verbose_name = 'Estruturas Complementares'

        def __str__(self):
            return self.atividades_complementares.nome

Estruturas Complementares:

    class Estruturas_complementares(models.Model):
    property = models.ForeignKey(Passivo,
                                 related_name='complementares',
                                 on_delete=models.CASCADE, null=True)
    atividade = models.OneToOneField(Atividade_estruturas_complementares, on_delete=models.PROTECT, related_name='atividade_estruturas_complementares')
    comprimento = models.DecimalField(
        'Comprimento', max_digits=10, decimal_places=2, blank=True, null=True, default=None)
    largura_altura = models.DecimalField(
        'Largura / Altura', max_digits=6, decimal_places=2, blank=True, null=True)
    profundidade = models.DecimalField(
        'Profundidade', max_digits=10, decimal_places=2, blank=True, null=True, default=None)

    class Meta:
        verbose_name = 'Estruturas Complementares'
        verbose_name_plural = 'Estruturas Complementares'

Faced with this situation in the class Activities_structures_complementary I would like to return the name of the activity that is in the activity class, but I’m not getting it, because I have no idea how to do this. The example:

    def __str__(self):
            return self.atividades_complementares.nome

returns the following error in tamplate:

My idea in creating this structure is to restrict the inclusion of activities that are not related. Hence the intermediate class.

In case you need any more information, I’m available. And as I am an intern and without any person in the area with experience to assist I am open to any kind of suggestion to better implement that solution.

Answer 1

Good in M2m ratio, you can use it like this:

py.models

class Atividade_estruturas_complementares(models.Model):
        atividades_complementares = models.ManyToManyField(Atividade)

        class Meta:
            verbose_name_plural = 'Estruturas Complementares'
            verbose_name = 'Estruturas Complementares'

        @property
        def m2m_nome(self):
            return self.atividades_complementares.nome

admin py.

list_display = ('m2m_nome',)

NOTE: There are some limitations with Manyrelatedmanager, check here this topical.

Answer 2

Hello, my solution was instead of using M2m was to use 1to1 in the activity class:

class Atividade_estruturas_complementares(models.Model):
atividades_complementares = models.OneToOneField(Atividade, on_delete=models.PROTECT,
                                                 related_name='atividades_complementares')

class Meta:
    verbose_name_plural = 'Estruturas Complementares'
    verbose_name = 'Estruturas Complementares'

def __str__(self):
    return self.atividades_complementares.nome

Already in the Structures_complementary class I had to change the field from 1to1 to a foreignKey as you can see below.

class Estruturas_complementares(models.Model):
passivo_id = models.ForeignKey(Passivo,
                             related_name='complementares',
                             on_delete=models.CASCADE)
atividade_complementar = models.ForeignKey(Atividade_estruturas_complementares, on_delete=models.PROTECT,
                                 related_name='atividade_estruturas_complementares')
comprimento = models.DecimalField(
    'Comprimento', max_digits=10, decimal_places=2, blank=True, null=True, default=None)
largura_altura = models.DecimalField(
    'Largura / Altura', max_digits=6, decimal_places=2, blank=True, null=True)
profundidade = models.DecimalField(
    'Profundidade', max_digits=10, decimal_places=2, blank=True, null=True, default=None)

class Meta:
    verbose_name = 'Estruturas Complementares'
    verbose_name_plural = 'Estruturas Complementares'
    unique_together = (('passivo_id', 'atividade_complementar'),)

def __str__(self):
    return self.atividade_complementar.atividades_complementares.nome

that way it was possible to get what I would like.