[Django] About users that can be used on template

Introduction

In Django, if you want to display the name of the currently logged-in user on the screen, you can do it by doing {{user.username}} or {{user.get_username}} on the template. But why can I use this variable ʻuser even though I haven't passed it to templets using the renderfunction in views.py or overriddenget_context_data ()` to add the variable? I had a question here, so I did some research.

Conclusion

The variables that can be used in the template are stored in the context (= {: , .....}), and this context roughly includes the following two types of variables.

1. Variables passed using render function etc. in views.py
2. Variables defined in the file specified by'context_processers' specified in the OPTION of TEMPLATES in settings.py

ʻUseris a variable that corresponds to the explanation of 2. There are other main variables that can be used without specifying it in views.py, such asrequest, perm, and message`.

Where it is stored

First, take a look at setting.py.

config/setting.py

#
#abridgement
#

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [os.path.join(BASE_DIR, 'templates')],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

#
#abridgement
#

The following four files are specified by TEMPLATES.OPTIONS.context_processors in setting.py. django.template.context_processors.debug django.template.context_processors.request Whereabouts of django.contrib.auth.context_processors.auth ・ ・ ・ ・ ・ ・ ʻuser django.contrib.messages.context_processors.messages`

Storage location of ʻuser`

python:django.contrib.auth.context_processors

#
#abridgement
#

def auth(request):
    """
    Return context variables required by apps that use Django's authentication
    system.

    If there is no 'user' attribute in the request, use AnonymousUser (from
    django.contrib.auth).
    """
    if hasattr(request, 'user'):
        user = request.user
    else:
        from django.contrib.auth.models import AnonymousUser
        user = AnonymousUser()

    return {
        'user': user,
        'perms': PermWrapper(user),
    }

By returning'user': user, ʻuser can be used in the template. After taking out the ʻusername attribute in ʻuser as ʻuser.username or instantiating the AnonymousUser class, use the get_user method in the class to set ʻuser.get_username` to change the logged-in user name. It can be displayed.

(reference)

At the bottom is the get_username function.

python:django.contrib.auth.models

class AnonymousUser:
    id = None
    pk = None
    username = ''
    is_staff = False
    is_active = False
    is_superuser = False
    _groups = EmptyManager(Group)
    _user_permissions = EmptyManager(Permission)

    def __str__(self):
        return 'AnonymousUser'

    def __eq__(self, other):
        return isinstance(other, self.__class__)

    def __hash__(self):
        return 1  # instances always return the same hash value

    def __int__(self):
        raise TypeError('Cannot cast AnonymousUser to int. Are you trying to use it in place of User?')

    def save(self):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def delete(self):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def set_password(self, raw_password):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def check_password(self, raw_password):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    @property
    def groups(self):
        return self._groups

    @property
    def user_permissions(self):
        return self._user_permissions

    def get_user_permissions(self, obj=None):
        return _user_get_permissions(self, obj, 'user')

    def get_group_permissions(self, obj=None):
        return set()

    def get_all_permissions(self, obj=None):
        return _user_get_permissions(self, obj, 'all')

    def has_perm(self, perm, obj=None):
        return _user_has_perm(self, perm, obj=obj)

    def has_perms(self, perm_list, obj=None):
        return all(self.has_perm(perm, obj) for perm in perm_list)

    def has_module_perms(self, module):
        return _user_has_module_perms(self, module)

    @property
    def is_anonymous(self):
        return True

    @property
    def is_authenticated(self):
        return False

    def get_username(self):
        return self.username