Python3.x 模型中的__str__方法在Django管理面板中生成大量重复查询

我有一辆Offer型车，它有一个前键，可以连接到另一辆Category型车.通过这个Category模型，我得到了与这个Category关联的Brand，并将其传递到管理页面上的Offer.但当我在Offer admin page的Dropdown Filter中使用这个Brand字段时，它会生成大量查询.

models.py

class Brand(BaseFields):
    name = models.CharField()
    ...
    def __str__(self):
        return self.name()

class Category(BaseFields):
    name = models.CharField()
    brand = models.ForeignKey(
        Brand,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
    )
    parents = models.ManyToManyField(
        'self',
        blank=True,
        verbose_name='Parent_category',
        related_name='children',
        symmetrical=False
    )
    
    def __str__(self):
        return str(self.brand) + '----' + self.name


class Offer(BaseFields):
    name = models.CharField()
    category = models.ForeignKey(
        Category,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='offer',
        verbose_name='Related_category'
    )

    def __str__(self):
        return self.name

admin.py

class OfferAdmin(admin.ModelAdmin):
    list_select_related = True
    list_display = (
        'name',
        'brand_name',
        'category',
        'place',
        'status'
    )
    list_editable = ('place', 'status')
    list_filter = (
        ('category__brand', RelatedOnlyDropdownFilter),
        ('category', RelatedOnlyDropdownFilter),
        'status'
    )
    fields = [
        'name',
        'description',
        'tech_info',
        'ctru',
        'category',
        'place',
        'status'
    ]
    autocomplete_fields = ['category']
    actions_on_bottom = True
    list_per_page = 25
    search_fields = ['name']

    def get_queryset(self, request):
        return super().get_queryset(request).select_related('category', 'category__brand')

    @admin.display(description='Brand', ordering='name')
    def brand_name(self, obj):
        return obj.category.brand.name

据我所知，这两个街区是主要问题

def __str__(self):
    return str(self.brand) + '----' + self.name

list_filter = (
        ('category__brand', RelatedOnlyDropdownFilter),
        ('category', RelatedOnlyDropdownFilter),
        'status'
    )

我需要减少通过计算Brand为所有提供生成的查询量.我确实知道我必须在某个地方使用select_related，但我只是不知道使用它的确切方法.