Django 500（内部服务器错误）。未能加载资源。Javascript

Question

从事Django项目。我正在尝试像Instagram一样实现follow按钮。当我按下follow按钮并更新后端的followers计数时，我正在尝试发送fetch请求。然后获取更新计数的响应，并更新页面上的innerHtml。但我得到了以下错误。 如果有人能帮我，那就太好了

index.js:13 Fetch failed loading: POST "http://127.0.0.1:8000/follow". It is showing error below in fetch code

failed to load resource: the server responded with a status of 500 (Internal Server Error)

这是我的密码：

网址 path("follow", views.follow, name="follow"),

模型

class User(AbstractUser):
    followersCount = models.IntegerField(blank=True)
    followingCount = models.IntegerField(blank=True)

    def __str__(self):
        return f"{self.username}"

class FollowList(models.Model):
    userName = models.CharField(max_length=64)
    followersList = models.ManyToManyField(User, blank=True, related_name="followers")
    followingList = models.ManyToManyField(User, blank=True, related_name="following")

视图：

@csrf_exempt
@login_required
def follow(request):
    # Composing a new email must be via POST
    if request.method != "POST":
        return JsonResponse({"error": "POST request required."}, status=400)

    # get data
    user = request.user
    currentUser = user.username
    a = User.objects.get(username = currentUser)

    data = json.loads(request.body)
    user_name = data.get("username")
    b = User.objects.get(username= user_name)
    status = data.get("status")
    try:
        a1 = FollowList.objects.get(username=currentUser)
        b1 = FollowList.objects.get(username=user_name)
    except FollowList.DoesNotExist:
        a1 = FollowList(username=currentUser)
        b1 = FollowList(username=user_name)
        a1.save()
        b1.save()

    if status == "Follow":        
        a1.followingList.add(b)
        b1.followersList.add(a)
        a1.save()
        b1.save()

        countA = a.followingCount
        countA = countA + 1
        a.followingCount = countA
        countB = b.followersCount
        countB = countB + 1
        b.followersCount = countB
        a.save()
        b.save()     
        
    else:
        a1.followingList.remove(b)
        b1.followersList.remove(a)
        a1.save()
        b1.save()

        countA = a.followingCount
        countA = countA - 1
        a.followingCount = countA
        countB = b.followersCount
        countB = countB - 1
        b.followersCount = countB
        a.save()
        b.save()

    bUser = User.objects.get(username = user_name)
    newFollowers = bUser.followersCount
    return JsonResponse({"newFollowersCount": f"{newFollowers}"}, status=201)

javaScript:

    const btn = document.querySelector("#followUnfollow");
    const user = document.querySelector("#username");
    const followers = document.querySelector("#followers");
    const follow_unfollow = btn.value; 
    document.getElementById("followUnfollow").onclick = function(){
        if (btn.value == "Follow"){
            document.getElementById("followUnfollow").value = "Unfollow";
        }else{
            document.getElementById("followUnfollow").value = "Follow";
        }
        console.log(user.innerHTML);   
        console.log(follow_unfollow);   
        fetch("/follow", {
            method: "POST",
            body: JSON.stringify({
                username: user.innerHTML,
                status: follow_unfollow,
            }),
        })
        

        .then(response => response.json())
        .then(result => {
            console.log(result);
            const newFollowers = result.newFollowersCount;
            followers.innerHTML = `${newFollowers}`;
        });
    };

});