Django属性错误：'function'对象没有属性'__self__'

Question

Django属性错误：'function'对象没有属性' self '

这是我的model.py文件，我收到以下错误：

from django.db import models

# Create your models here.
import uuid


from rgbfield.fields import RGBColorField

class Category(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    index = models.IntegerField(unique=True, db_index=True)
    name = models.CharField(unique=True, max_length=100)
    abbreviation = models.CharField(max_length=4, unique=True)
    theme_color = RGBColorField(default="#fff")
    text_color = RGBColorField(default="#000")

    def __str__(self):
        return self.name

class Tool(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    name = models.CharField(unique=True, db_index=True, max_length=100, help_text="The name of your tool (must be unique)")
    byline = models.CharField(max_length=100,help_text="The byline of your tool (can contain HTML)")
    description = models.TextField(help_text="A description of your tool (can contain HTML)")
    logo_image = models.ImageField(upload_to='image', blank=True, help_text="Use to upload an (optional) logo image for your tool")
    logo_link = models.URLField(blank=True, help_text="An (optional) link to be associated with your tool's logo")
    about_link = models.URLField(blank=True, help_text="An (optional) link to further information about your tool")
    install_link = models.URLField(blank=True, help_text="An (optional) link to local installation information for your tool")
    launch_link = models.URLField(blank=True, help_text="An (optional) link to launch your tool. If hosted by EMAC, leave this blank.")
    categories = models.ManyToManyField(Category, related_name="tools")
    is_external = models.BooleanField(default=True)

    def tool_directory_path(instance, filename):
    # Image file will be uploaded to MEDIA_ROOT/tools/<id>/<filename>
        return "tools/{0}/{1}".format(instance.id, filename)

    def __str__(self):
        return self.name

我已检查过所有内容，但不知道导致此错误的原因。任何导致错误的见解都会非常有用。

这是view.py文件

from django.shortcuts import render
from django.http import HttpResponse
from .models import Category, Tool

# Create your views here.
def homepage(request):

    category = Category.objects.all()
    tool = Tool.objects.all()

    context = {
        'Tool': tool,
        'Category': category,
    }

    return render(request, 'index.html',context)