自定义User模型登录异常：提交表单提示用户已存在，无法登录

核心原因 #

登录表单错误使用了ModelForm，而ModelForm会自动应用模型的唯一性校验（你的MyUser模型中username字段设置了unique=True）。提交登录请求时，表单会像注册一样检查用户名是否已存在，导致出现错误提示。同时表单的clean方法存在语法错误，authenticate参数使用也不符合Django规范。

分步修正 #

1. 修正表单（forms.py） #

将登录表单改为普通Form而非ModelForm，移除不必要的字段，修复clean方法的语法错误，仅保留登录必需的用户名和密码：

from . import models
from django import forms
from django.contrib.auth import authenticate

class MyUserForm(forms.ModelForm):
    # 注册表单保持不变
    class Meta():
        model = models.MyUser
        fields = ('username','email','password','organisation')

class MyUserLoginForm(forms.Form):
    # 登录表单改用普通Form
    username = forms.CharField(label="用户名")
    password = forms.CharField(label="密码", widget=forms.PasswordInput)

    def clean(self):
        cleaned_data = super().clean()
        username = cleaned_data.get('username')
        password = cleaned_data.get('password')

        if username and password:
            user = authenticate(username=username, password=password)
            if not user:
                raise forms.ValidationError("登录信息无效，请检查用户名和密码")
        return cleaned_data

2. 修正登录视图（views.py） #

简化登录逻辑，无需获取email和organisation，直接从表单的cleaned_data中取用户名和密码：

from django.shortcuts import render, redirect
from django.views.generic import TemplateView,CreateView
from django.contrib.auth.mixins import LoginRequiredMixin
from django.urls import reverse_lazy
from . import models
from . import forms
from django.contrib.auth import authenticate,login

class indexPage(TemplateView):
    template_name = 'accounts/inner_index.html'

class Create_Organisation(CreateView):
    model = models.Organisation
    fields = ('__all__')
    template_name  = 'accounts/organisation_form.html'
    success_url = reverse_lazy("accounts:inner_index")

class Create_Accounts(CreateView,LoginRequiredMixin):
    model = models.MyUser
    form_class = forms.MyUserForm
    template_name = 'accounts/create_account.html'
    success_url = reverse_lazy("accounts:inner_index")

def login_my_user(request):
    if request.method=="POST":
        form=forms.MyUserLoginForm(request.POST)
        if form.is_valid():
            username = form.cleaned_data.get('username')
            password = form.cleaned_data.get('password')
            user = authenticate(username=username, password=password)
            if user:
                login(request, user)
                return redirect("home")
    else:
        form=forms.MyUserLoginForm()

    return render(request,"accounts/login_account.html",{'form':form})

3. 登录模板（login_account.html） #

模板会自动适配新表单，仅显示用户名和密码字段，无需额外修改：

{% extends 'base.html' %}
{% load bootstrap3 %}
{% block body_block %}
<form class="" method="post">
  {% csrf_token %}
  {% bootstrap_form form %}
  <input type="submit" name="" value="登录">
</form>
{% endblock %}

额外补充：登出功能实现 #

如果需要完善登出功能，可在views.py中添加：

def logout_my_user(request):
    logout(request)
    return redirect("accounts:inner_index")

并在urls.py中添加路由：

path('logout/', views.logout_my_user, name='logout'),

内容的提问来源于stack exchange，提问作者Rahul