Django：一个模型中的多个泛型关系是糟糕的设计吗？答案

【问题标题】：Django: Are multiple Generic Relations in one Model bad design?Django：一个模型中的多个泛型关系是糟糕的设计吗？
【发布时间】：2013-07-15 07:56:43
【问题描述】：

我有一个具有多个通用关系的模型，在我的模板中使用它变得非常复杂。该模型是在“场地”和/或“音乐节”上举行的“演出”或音乐活动，并具有“音乐家”和/或“合奏团”。

复杂的地方在于，每个“演出”都有一个演示者、发起人和一个代理。这些被设置为与其他模型（例如“PresenterCompany”）的通用关系。演示者公司可以是同一演出的发起人、演示者或代理，或所有这些人。以下是模型（为参考简化）：

class Gig(models.Model):
    description = models.CharField(max_length=100, blank=True)
    date = models.DateTimeField()
    venue = models.ForeignKey(Venue)
    festival = models.ForeignKey(Festival, blank = True, null=True)
    musician = models.ManyToManyField(Musician, blank=True)
    ensembles = models.ManyToManyField(Ensemble, blank = True)

    presenter_content_type = models.ForeignKey(ContentType,
        limit_choices_to={"model__in": ("Individual", "ArtsOrganization",'Presenter', "BookingAgent","Festival", "OtherOrganization","PresenterCompany", "Venue")}, related_name = "Presenter Type", verbose_name = "Presenter",blank=True, null=True)
    presenter_id = models.IntegerField(db_index=True, blank=True, null=True, verbose_name='Presenter ID')
    presenter = generic.GenericForeignKey('presenter_content_type','presenter_id')

    promoter_content_type = models.ForeignKey(ContentType,
        limit_choices_to={"model__in": ("Individual", "ArtsOrganization","BookingAgent","Presenter", "Festival", "OtherOrganization","PresenterCompany", "Venue")}, related_name = "promotor", verbose_name='Promoter Type', blank=True, null=True)
    promoter_id = models.IntegerField(db_index=True, blank=True, null=True, verbose_name='Promoter ID')
    promoter = generic.GenericForeignKey('promoter_content_type','promoter_id')

    agent_content_type = models.ForeignKey(ContentType,
        limit_choices_to={"model__in": ("Individual", "BookingAgent")}, related_name="agent", verbose_name='Agent Type', blank=True, null=True)
    agent_id = models.IntegerField(db_index=True, blank=True, null=True, verbose_name='Agent ID')
    agent = generic.GenericForeignKey('agent_content_type','agent_id')


class PresenterCompany(models.Model):
    name = models.CharField(max_length=70)
    address =GenericRelation(Address)
    presented_gig = GenericRelation('Gig',
        content_type_field='presenter_content_type',
        object_id_field='presenter_id',
        related_name='presenter_presented_gig'
    )

    promoted_gig = GenericRelation('Gig',
        content_type_field='promoter_content_type',
        object_id_field='promoter_id',
        related_name='presenter_promoted_gig'
    )
    booked_gig = GenericRelation('Gig',
        content_type_field='promoter_content_type',
        object_id_field='promoter_id',
        related_name='presenter_booked_gig'
    )

主要问题是，当我尝试为演示者公司获取所有演出时，我必须为每个角色编写三个不同的 for 循环，即 {% for gig in presentercompany.presented_gig.all %}，依此类推...这似乎是多余的代码。

有没有更好的方法来构建它，例如为演示者、推广者和代理使用中间模型？谢谢你的建议！

【问题讨论】：

标签： django models generic-relations

【解决方案1】：

一般的关系肯定很难处理。我只会在没有其他选择时使用它们。

在您的情况下，我看到了其他几个选项。您可以在 PresenterCompany 和 Gig 之间建立多对多关系，使用直通表指定关系类型 (https://docs.djangoproject.com/en/2.0/topics/db/models/#extra-fields-on-many-to-many-relationships)：

class Gig(models.Model):
    description = models.CharField(max_length=100, blank=True)
    date = models.DateTimeField()
    venue = models.ForeignKey(Venue)
    festival = models.ForeignKey(Festival, blank=True, null=True)
    musician = models.ManyToManyField(Musician, blank=True)
    ensembles = models.ManyToManyField(Ensemble, blank=True)


class PresenterCompanyGigRelationship(models.Model):
    gig = models.ForeignKey(Gig, on_delete=models.CASCADE)
    presenter_company = models.ForeignKey(
        'PresenterCompany', on_delete=models.CASCADE)
    relationship = models.CharField(
        max_length=10,
        choices=(
            ('presenter', 'Presenter'),
            ('promoter', 'Promoter'),
            ('agent', 'Agent'),
            ))


class PresenterCompany(models.Model):
    name = models.CharField(max_length=70)
    git = models.ManyToManyField(Gig, through=PresenterCompanyGigRelationship)

【讨论】：