Python ValueError：字段'；长度'；应为一个数字，但得到''；

型号

from django.db import models
from django.contrib.auth.models import User
from django.utils.timezone import now
from django.contrib.auth.models import User

# Create your models here.

class Allmusic(models.Model):
    sno=models.AutoField(primary_key=True)
    name=models.CharField(max_length=100,default="")
    author=models.CharField(max_length=100,default="")
    description=models.TextField(default="")
    movie=models.CharField(max_length=100,default="")
    category=models.CharField(max_length=100,default="")
    subcategory=models.CharField(max_length=100,default="")
    image=models.ImageField(upload_to='images', default="")
    musicfile=models.FileField(upload_to='music_file', default="")

    def __str__(self):
        return self.name  

class Watchlater(models.Model):
    watch_id=models.AutoField(primary_key=True)
    user=models.ForeignKey(User,on_delete=models.CASCADE)
    video_id=models.CharField(max_length=100000,default="")
    

class BlogComment(models.Model):
    sno=models.AutoField(primary_key=True)
    comment=models.TextField()
    user=models.ForeignKey(User,on_delete=models.CASCADE)
    post=models.ForeignKey(Allmusic,on_delete=models.CASCADE)
    timestamp=models.DateTimeField(default=now)


class History(models.Model):
    history_id=models.AutoField(primary_key=True)
    user=models.ForeignKey(User,on_delete=models.CASCADE)
    music_id=models.CharField(max_length=100000,default="")
    

views.py

from django.shortcuts import render,HttpResponse,redirect
from .models import Allmusic,Watchlater,BlogComment,History
from math import ceil
from django.contrib.auth.models import User
from django.contrib.auth import login,authenticate,logout
from django.contrib import messages
from django.db.models import Case,When

# Create your views here.

def home(request):  
    return render(request,'home.html')

def index(request):
    allProds = []
    catprods = Allmusic.objects.values('category', 'sno')
    cats = {item['category'] for item in catprods}
    for cat in cats:
        prod = Allmusic.objects.filter(category=cat)
        n = len(prod)
        nSlides = n // 4 + ceil((n / 4) - (n // 4))
        allProds.append([prod, range(1, nSlides), nSlides])
    params = {'allProds':allProds}
    return render(request,'index.html',params)

def indexmovie(request):
    allProds = []
    catprods = Allmusic.objects.values('movie', 'sno')
    cats = {item['movie'] for item in catprods}
    for cat in cats:
        prod = Allmusic.objects.filter(movie=cat)
        n = len(prod)
        nSlides = n // 4 + ceil((n / 4) - (n // 4))
        allProds.append([prod, range(1, nSlides), nSlides])
    params = {'allProds':allProds}
    return render(request,'indexmovie.html',params)
    
def about(request):
    return render(request,'about.html')

def contact(request):
    return render(request,'contact.html')

#Authenciation APIs
def handleSignup(request):
     if request.method=='POST':
          #Get the post parameters
          username=request.POST['username']
          fname=request.POST['fname']
          lname=request.POST['lname']
          email=request.POST['email']
          pass1=request.POST['pass1']
          pass2=request.POST['pass2']

          #checks for errorneous input
          #username should be <10
          # username shouldbe alphanumeric

          if len(username)>10:
                messages.error(request,"username must be less than 10 characters")
                return redirect('/')
          if not username.isalnum():
                messages.error(request,"username should only contain letters and numbers")
                return redirect('/')
          if pass1!=pass2:
               messages.error(request,"Password do not match")
               return redirect('/')

          #Create the user
          myuser=User.objects.create_user(username,email,pass1)
          myuser.first_name=fname
          myuser.last_name=lname
          myuser.save()

          messages.success(request,"your Musify account has been created succesfully Now go enter your credentials into the login form")
          return redirect('/')

     else:
          return HttpResponse('404 - Not Found')

def handleLogin(request):
     if request.method=='POST':

          #Get the post parameters
          loginusername=request.POST['loginusername']
          loginpassword=request.POST['loginpassword']

          user=authenticate(username=loginusername,password=loginpassword)

          if user is not None:
               login(request,user)
               messages.success(request,"succesfully Logged In")
               return redirect('/')              
          else:
               messages.error(request,"Invalid credentials Please try again")
               return redirect('/')
               
               
     return HttpResponse('404 - Not Found')

def handleLogout(request):
    logout(request)
    messages.success(request,"succesully Logout")
    return redirect('/')


def watchlater(request):
    if request.method=="POST":
        user=request.user
        video_id=request.POST['video_id']

        watch=Watchlater.objects.filter(user=user)
        for i in watch:
            if video_id==i.video_id:
                messages.success(request,"Song is already added")
                break
        else:
            wl=Watchlater(user=user,video_id=video_id)
            wl.save()
            messages.success(request,"Song added to watch later")
        return redirect(f"/index/subpage/{video_id}")
    wl=Watchlater.objects.filter(user=request.user)
    ids=[]
    for i in wl:
        ids.append(i.video_id)
    
    preserved=Case(*[When(pk=pk,then=pos) for pos,pk in enumerate(ids)])
    song=Allmusic.objects.filter(sno__in=ids).order_by(preserved)
    
    return render(request,'watchlater.html',{'song':song})

def subpage(request,sno):
    post=Allmusic.objects.filter(sno=sno)
    comment=BlogComment.objects.filter(post=sno)
    context={'post':post,'comment':comment}
    return render(request,'subpage.html',context)

def postComment(request):
    comment=request.POST.get("comment")
    user=request.user
    postSno=request.POST.get("postSno")
    post=Allmusic.objects.get(sno=postSno)
    comment=BlogComment(comment=comment,user=user,post=post)
    comment.save()
    messages.success(request,"your comment has been posted")
    return redirect(f"index/subpage/{post.sno}")
   


def history(request):
    if request.method == "POST":
        user=request.user
        music_id=request.POST['music_id']
        history=History(user=user,music_id=music_id)
        history.save()

        print(history)
        return redirect(f"/index/subpage/{music_id}")

    history=History.objects.filter(user=request.user)
    ids=[]
    for i in history:
        ids.append(i.music_id)
    
    preserved=Case(*[When(pk=pk,then=pos) for pos,pk in enumerate(ids)])
    song=Allmusic.objects.filter(sno__in=ids).order_by(preserved)
    
    return render(request,'history.html',{"history":song})

# Generated by Django 3.1 on 2020-10-03 12:49

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('ddsmusic', '0013_auto_20201002_2135'),
    ]

    operations = [
        migrations.AddField(
            model_name='allmusic',
            name='length',
            field=models.IntegerField(default=2),
        ),
    ]

0014\u allmusic\u length.py

from django.shortcuts import render,HttpResponse,redirect
from .models import Allmusic,Watchlater,BlogComment,History
from math import ceil
from django.contrib.auth.models import User
from django.contrib.auth import login,authenticate,logout
from django.contrib import messages
from django.db.models import Case,When

# Create your views here.

def home(request):  
    return render(request,'home.html')

def index(request):
    allProds = []
    catprods = Allmusic.objects.values('category', 'sno')
    cats = {item['category'] for item in catprods}
    for cat in cats:
        prod = Allmusic.objects.filter(category=cat)
        n = len(prod)
        nSlides = n // 4 + ceil((n / 4) - (n // 4))
        allProds.append([prod, range(1, nSlides), nSlides])
    params = {'allProds':allProds}
    return render(request,'index.html',params)

def indexmovie(request):
    allProds = []
    catprods = Allmusic.objects.values('movie', 'sno')
    cats = {item['movie'] for item in catprods}
    for cat in cats:
        prod = Allmusic.objects.filter(movie=cat)
        n = len(prod)
        nSlides = n // 4 + ceil((n / 4) - (n // 4))
        allProds.append([prod, range(1, nSlides), nSlides])
    params = {'allProds':allProds}
    return render(request,'indexmovie.html',params)
    
def about(request):
    return render(request,'about.html')

def contact(request):
    return render(request,'contact.html')

#Authenciation APIs
def handleSignup(request):
     if request.method=='POST':
          #Get the post parameters
          username=request.POST['username']
          fname=request.POST['fname']
          lname=request.POST['lname']
          email=request.POST['email']
          pass1=request.POST['pass1']
          pass2=request.POST['pass2']

          #checks for errorneous input
          #username should be <10
          # username shouldbe alphanumeric

          if len(username)>10:
                messages.error(request,"username must be less than 10 characters")
                return redirect('/')
          if not username.isalnum():
                messages.error(request,"username should only contain letters and numbers")
                return redirect('/')
          if pass1!=pass2:
               messages.error(request,"Password do not match")
               return redirect('/')

          #Create the user
          myuser=User.objects.create_user(username,email,pass1)
          myuser.first_name=fname
          myuser.last_name=lname
          myuser.save()

          messages.success(request,"your Musify account has been created succesfully Now go enter your credentials into the login form")
          return redirect('/')

     else:
          return HttpResponse('404 - Not Found')

def handleLogin(request):
     if request.method=='POST':

          #Get the post parameters
          loginusername=request.POST['loginusername']
          loginpassword=request.POST['loginpassword']

          user=authenticate(username=loginusername,password=loginpassword)

          if user is not None:
               login(request,user)
               messages.success(request,"succesfully Logged In")
               return redirect('/')              
          else:
               messages.error(request,"Invalid credentials Please try again")
               return redirect('/')
               
               
     return HttpResponse('404 - Not Found')

def handleLogout(request):
    logout(request)
    messages.success(request,"succesully Logout")
    return redirect('/')


def watchlater(request):
    if request.method=="POST":
        user=request.user
        video_id=request.POST['video_id']

        watch=Watchlater.objects.filter(user=user)
        for i in watch:
            if video_id==i.video_id:
                messages.success(request,"Song is already added")
                break
        else:
            wl=Watchlater(user=user,video_id=video_id)
            wl.save()
            messages.success(request,"Song added to watch later")
        return redirect(f"/index/subpage/{video_id}")
    wl=Watchlater.objects.filter(user=request.user)
    ids=[]
    for i in wl:
        ids.append(i.video_id)
    
    preserved=Case(*[When(pk=pk,then=pos) for pos,pk in enumerate(ids)])
    song=Allmusic.objects.filter(sno__in=ids).order_by(preserved)
    
    return render(request,'watchlater.html',{'song':song})

def subpage(request,sno):
    post=Allmusic.objects.filter(sno=sno)
    comment=BlogComment.objects.filter(post=sno)
    context={'post':post,'comment':comment}
    return render(request,'subpage.html',context)

def postComment(request):
    comment=request.POST.get("comment")
    user=request.user
    postSno=request.POST.get("postSno")
    post=Allmusic.objects.get(sno=postSno)
    comment=BlogComment(comment=comment,user=user,post=post)
    comment.save()
    messages.success(request,"your comment has been posted")
    return redirect(f"index/subpage/{post.sno}")
   


def history(request):
    if request.method == "POST":
        user=request.user
        music_id=request.POST['music_id']
        history=History(user=user,music_id=music_id)
        history.save()

        print(history)
        return redirect(f"/index/subpage/{music_id}")

    history=History.objects.filter(user=request.user)
    ids=[]
    for i in history:
        ids.append(i.music_id)
    
    preserved=Case(*[When(pk=pk,then=pos) for pos,pk in enumerate(ids)])
    song=Allmusic.objects.filter(sno__in=ids).order_by(preserved)
    
    return render(request,'history.html',{"history":song})

# Generated by Django 3.1 on 2020-10-03 12:49

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('ddsmusic', '0013_auto_20201002_2135'),
    ]

    operations = [
        migrations.AddField(
            model_name='allmusic',
            name='length',
            field=models.IntegerField(default=2),
        ),
    ]

---

ddsmusic.0014_allmusic_length

迁移文件是什么样子的？当我运行命令python manage.py migrateDhruvilShah时，会出现上述错误：但它源自您构建的迁移文件。因此，模型等都与此特定问题无关。以下是文件Willem Van Onsem“”#由Django 3.1于2020-10-03 12:49从Django.db导入迁移生成，模型类迁移（migrations.Migration）：依赖项=[（'ddsmusic'，'0013_auto_20201002_2135'），]操作=[migrations.AddField（model_name='allmusic'，name='length'，field=models.IntegerField（默认值=''），]“很明显，您添加了一个

length

字段，其中

default='

。您可能从模型中删除了该字段，但没有从迁移文件中删除，因此它将继续阻塞。您应该删除迁移文件（以及其他相关迁移文件）。