Writing the Post Model
Follow the step-by-step instructions to create the Post model.
We'll cover the following...
We'll cover the following...
Now we have all the things we need to write better code, as less of it, let’s write the Post model.
We have already established the structure of the Post model. Let’s write the code and the features:
Creating the post app
Create a new application called post:
django-admin startapp post
Click the “Run” button and execute the given command:
import errno
import os
import re
import socket
import sys
from datetime import datetime
from django.conf import settings
from django.core.management.base import BaseCommand, CommandError
from django.core.servers.basehttp import WSGIServer, get_internal_wsgi_application, run
from django.utils import autoreload
from django.utils.regex_helper import _lazy_re_compile
naiveip_re = _lazy_re_compile(
r"""^(?:
(?P<addr>
(?P<ipv4>\d{1,3}(?:\.\d{1,3}){3}) | # IPv4 address
(?P<ipv6>\[[a-fA-F0-9:]+\]) | # IPv6 address
(?P<fqdn>[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*) # FQDN
):)?(?P<port>\d+)$""",
re.X,
)
class Command(BaseCommand):
help = "Starts a lightweight web server for development."
# Validation is called explicitly each time the server is reloaded.
requires_system_checks = []
stealth_options = ("shutdown_message",)
suppressed_base_arguments = {"--verbosity", "--traceback"}
default_addr = "0.0.0.0"
default_addr_ipv6 = "::1"
default_port = "8000"
protocol = "http"
server_cls = WSGIServer
def add_arguments(self, parser):
parser.add_argument(
"addrport", nargs="?", help="Optional port number, or ipaddr:port"
)
parser.add_argument(
"--ipv6",
"-6",
action="store_true",
dest="use_ipv6",
help="Tells Django to use an IPv6 address.",
)
parser.add_argument(
"--nothreading",
action="store_false",
dest="use_threading",
help="Tells Django to NOT use threading.",
)
parser.add_argument(
"--noreload",
action="store_false",
dest="use_reloader",
help="Tells Django to NOT use the auto-reloader.",
)
parser.add_argument(
"--skip-checks",
action="store_true",
help="Skip system checks.",
)
def execute(self, *args, **options):
if options["no_color"]:
# We rely on the environment because it's currently the only
# way to reach WSGIRequestHandler. This seems an acceptable
# compromise considering `runserver` runs indefinitely.
os.environ["DJANGO_COLORS"] = "nocolor"
super().execute(*args, **options)
def get_handler(self, *args, **options):
"""Return the default WSGI handler for the runner."""
return get_internal_wsgi_application()
def handle(self, *args, **options):
if not settings.DEBUG and not settings.ALLOWED_HOSTS:
raise CommandError("You must set settings.ALLOWED_HOSTS if DEBUG is False.")
self.use_ipv6 = options["use_ipv6"]
if self.use_ipv6 and not socket.has_ipv6:
raise CommandError("Your Python does not support IPv6.")
self._raw_ipv6 = False
if not options["addrport"]:
self.addr = ""
self.port = self.default_port
else:
m = re.match(naiveip_re, options["addrport"])
if m is None:
raise CommandError(
'"%s" is not a valid port number '
"or address:port pair." % options["addrport"]
)
self.addr, _ipv4, _ipv6, _fqdn, self.port = m.groups()
if not self.port.isdigit():
raise CommandError("%r is not a valid port number." % self.port)
if self.addr:
if _ipv6:
self.addr = self.addr[1:-1]
self.use_ipv6 = True
self._raw_ipv6 = True
elif self.use_ipv6 and not _fqdn:
raise CommandError('"%s" is not a valid IPv6 address.' % self.addr)
if not self.addr:
self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
self._raw_ipv6 = self.use_ipv6
self.run(**options)
def run(self, **options):
"""Run the server, using the autoreloader if needed."""
use_reloader = options["use_reloader"]
if use_reloader:
autoreload.run_with_reloader(self.inner_run, **options)
else:
self.inner_run(None, **options)
def inner_run(self, *args, **options):
# If an exception was silenced in ManagementUtility.execute in order
# to be raised in the child process, raise it now.
autoreload.raise_last_exception()
threading = options["use_threading"]
# 'shutdown_message' is a stealth option.
shutdown_message = options.get("shutdown_message", "")
if not options["skip_checks"]:
self.stdout.write("Performing system checks...\n\n")
self.check(display_num_errors=True)
# Need to check migrations here, so can't use the
# requires_migrations_check attribute.
self.check_migrations()
try:
handler = self.get_handler(*args, **options)
run(
self.addr,
int(self.port),
handler,
ipv6=self.use_ipv6,
threading=threading,
on_bind=self.on_bind,
server_cls=self.server_cls,
)
except OSError as e:
# Use helpful error messages instead of ugly tracebacks.
ERRORS = {
errno.EACCES: "You don't have permission to access that port.",
errno.EADDRINUSE: "That port is already in use.",
errno.EADDRNOTAVAIL: "That IP address can't be assigned to.",
}
try:
error_text = ERRORS[e.errno]
except KeyError:
error_text = e
self.stderr.write("Error: %s" % error_text)
# Need to use an OS exit because sys.exit doesn't work in a thread
os._exit(1)
except KeyboardInterrupt:
if shutdown_message:
self.stdout.write(shutdown_message)
sys.exit(0)
def on_bind(self, server_port):
quit_command = "CTRL-BREAK" if sys.platform == "win32" else "CONTROL-C"
if self._raw_ipv6:
addr = f"[{self.addr}]"
elif self.addr == "0":
addr = "0.0.0.0"
else:
addr = self.addr
now = datetime.now().strftime("%B %d, %Y - %X")
version = self.get_version()
print(
f"{now}\n"
f"Django version {version}, using settings {settings.SETTINGS_MODULE!r}\n"
f"Starting development server at {self.protocol}://{addr}:{server_port}/\n"
f"Quit the server with {quit_command}.",
file=self.stdout,
)Implementing abstraction for reducing code duplication
Rewrite apps.py of the new create package so it can be called easily in the project:
from django.apps import AppConfigclass PostConfig(AppConfig):default_auto_field = 'django.db.models.BigAutoField'name = 'core.post'label = "core_post"
The Post model
Once that’s done, we can now write the Post model. Open the models.py file and enter the following content:
import errno
import os
import re
import socket
import sys
from datetime import datetime
from django.conf import settings
from django.core.management.base import BaseCommand, CommandError
from django.core.servers.basehttp import WSGIServer, get_internal_wsgi_application, run
from django.utils import autoreload
from django.utils.regex_helper import _lazy_re_compile
naiveip_re = _lazy_re_compile(
r"""^(?:
(?P<addr>
(?P<ipv4>\d{1,3}(?:\.\d{1,3}){3}) | # IPv4 address
(?P<ipv6>\[[a-fA-F0-9:]+\]) | # IPv6 address
(?P<fqdn>[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*) # FQDN
):)?(?P<port>\d+)$""",
re.X,
)
class Command(BaseCommand):
help = "Starts a lightweight web server for development."
# Validation is called explicitly each time the server is reloaded.
requires_system_checks = []
stealth_options = ("shutdown_message",)
suppressed_base_arguments = {"--verbosity", "--traceback"}
default_addr = "0.0.0.0"
default_addr_ipv6 = "::1"
default_port = "8000"
protocol = "http"
server_cls = WSGIServer
def add_arguments(self, parser):
parser.add_argument(
"addrport", nargs="?", help="Optional port number, or ipaddr:port"
)
parser.add_argument(
"--ipv6",
"-6",
action="store_true",
dest="use_ipv6",
help="Tells Django to use an IPv6 address.",
)
parser.add_argument(
"--nothreading",
action="store_false",
dest="use_threading",
help="Tells Django to NOT use threading.",
)
parser.add_argument(
"--noreload",
action="store_false",
dest="use_reloader",
help="Tells Django to NOT use the auto-reloader.",
)
parser.add_argument(
"--skip-checks",
action="store_true",
help="Skip system checks.",
)
def execute(self, *args, **options):
if options["no_color"]:
# We rely on the environment because it's currently the only
# way to reach WSGIRequestHandler. This seems an acceptable
# compromise considering `runserver` runs indefinitely.
os.environ["DJANGO_COLORS"] = "nocolor"
super().execute(*args, **options)
def get_handler(self, *args, **options):
"""Return the default WSGI handler for the runner."""
return get_internal_wsgi_application()
def handle(self, *args, **options):
if not settings.DEBUG and not settings.ALLOWED_HOSTS:
raise CommandError("You must set settings.ALLOWED_HOSTS if DEBUG is False.")
self.use_ipv6 = options["use_ipv6"]
if self.use_ipv6 and not socket.has_ipv6:
raise CommandError("Your Python does not support IPv6.")
self._raw_ipv6 = False
if not options["addrport"]:
self.addr = ""
self.port = self.default_port
else:
m = re.match(naiveip_re, options["addrport"])
if m is None:
raise CommandError(
'"%s" is not a valid port number '
"or address:port pair." % options["addrport"]
)
self.addr, _ipv4, _ipv6, _fqdn, self.port = m.groups()
if not self.port.isdigit():
raise CommandError("%r is not a valid port number." % self.port)
if self.addr:
if _ipv6:
self.addr = self.addr[1:-1]
self.use_ipv6 = True
self._raw_ipv6 = True
elif self.use_ipv6 and not _fqdn:
raise CommandError('"%s" is not a valid IPv6 address.' % self.addr)
if not self.addr:
self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
self._raw_ipv6 = self.use_ipv6
self.run(**options)
def run(self, **options):
"""Run the server, using the autoreloader if needed."""
use_reloader = options["use_reloader"]
if use_reloader:
autoreload.run_with_reloader(self.inner_run, **options)
else:
self.inner_run(None, **options)
def inner_run(self, *args, **options):
# If an exception was silenced in ManagementUtility.execute in order
# to be raised in the child process, raise it now.
autoreload.raise_last_exception()
threading = options["use_threading"]
# 'shutdown_message' is a stealth option.
shutdown_message = options.get("shutdown_message", "")
if not options["skip_checks"]:
self.stdout.write("Performing system checks...\n\n")
self.check(display_num_errors=True)
# Need to check migrations here, so can't use the
# requires_migrations_check attribute.
self.check_migrations()
try:
handler = self.get_handler(*args, **options)
run(
self.addr,
int(self.port),
handler,
ipv6=self.use_ipv6,
threading=threading,
on_bind=self.on_bind,
server_cls=self.server_cls,
)
except OSError as e:
# Use helpful error messages instead of ugly tracebacks.
ERRORS = {
errno.EACCES: "You don't have permission to access that port.",
errno.EADDRINUSE: "That port is already in use.",
errno.EADDRNOTAVAIL: "That IP address can't be assigned to.",
}
try:
error_text = ERRORS[e.errno]
except KeyError:
error_text = e
self.stderr.write("Error: %s" % error_text)
# Need to use an OS exit because sys.exit doesn't work in a thread
os._exit(1)
except KeyboardInterrupt:
if shutdown_message:
self.stdout.write(shutdown_message)
sys.exit(0)
def on_bind(self, server_port):
quit_command = "CTRL-BREAK" if sys.platform == "win32" else "CONTROL-C"
if self._raw_ipv6:
addr = f"[{self.addr}]"
elif self.addr == "0":
addr = "0.0.0.0"
else:
addr = self.addr
now = datetime.now().strftime("%B %d, %Y - %X")
version = self.get_version()
print(
f"{now}\n"
f"Django version {version}, using settings {settings.SETTINGS_MODULE!r}\n"
f"Starting development server at {self.protocol}://{addr}:{server_port}/\n"
f"Quit the server with {quit_command}.",
file=self.stdout,
)Adding the Post class in the models.py file
Foreign key
You can see here how we created the ForeignKey relationship. Django models actually provide tools to handle this kind of relationship. It’s also symmetrical, meaning that not only can we use the ...