jacklinke · January 13, 2021 14:41 · Jan 13, 2021
diff --git a/cheatsheet.py b/cheatsheet.py
@@ -0,0 +1,197 @@
+import uuid
+from django.db import models
+# Use the import below instead, if using GeoDjango fields
+# from django.contrib.gis.db import models
+from django.utils.translation import ugettext_lazy as _
+
+from django.contrib.postgres.fields import (
+    ArrayField,
+    CICharField,
+    CIEmailField,
+    CITextField,
+    HStoreField,
+    IntegerRangeField,
+    BigIntegerRangeField,
+    DecimalRangeField,
+    DateTimeRangeField,
+    DateRangeField,
+)
+
+
+def file_directory_path(instance, filename):
+    # file will be uploaded to MEDIA_ROOT/my_files/{id}/{year}/{month}/{filename}
+    return f"my_files/{instance.id}/{timezone.now().date().strftime('%Y/%m')}/{filename}"
+
+
+def create_rand_value(app_label, model_name, prefix=None, suffix_len=10):
+    """
+    Just an example function, used to demonstrate overriding save()
+    It generates an easily readable, unique string
+    """
+
+    code = ""
+
+    if prefix is not None:
+        code = code.join(prefix).join("-")
+
+    while True:
+        code = code.join(random.SystemRandom().choice("23456789BCDFGHJKMNPQRSTVWXYZ") for _ in range(suffix_len))
+        Model = apps.get_model(app_label=app_label, model_name=model_name)
+
+        try:
+            present = Model.objects.first()
+        except Model.DoesNotExist:
+            present = None
+
+        if present is not None:
+            if not Model.objects.filter(code=code).exists():
+                return code
+
+
+# https://docs.djangoproject.com/en/3.1/topics/db/managers/#from-queryset
+class MyModelQuerySet(models.QuerySet):
+    """Used when we need to return a queryset that has been filtered in some way"""
+    def manager_and_queryset_method(self):
+        return
+
+
+class MyModelManager(models.Manager):
+    """Used when we need a table-level method that does NOT return a queryset"""
+    def manager_only_method(self):
+        return
+
+
+CombinedMyModelManager = MyModelManager.from_queryset(MyModelQuerySet)
+
+
+class MyModel(models.Model):
+    """Comment"""
+
+    class CompanyType(models.TextChoices):
+        PUBLIC_LIMITED_COMPANY = 'PLC', _('Public Limited Company')
+        PRIVATE_COMPANY_LIMITED = 'LTD', _('Private Company limited by shares')
+        LIMITED_LIABILITY_PARTNERSHIP = 'LLP', _('Limited Liability Partnership')
+        __empty__ = _('(Unknown)')
+
+    # https://docs.djangoproject.com/en/3.1/ref/models/fields/
+    boolean_field = models.BooleanField(_("Boolean"), default=False)
+    char_field = models.CharField(_("Character"), max_length=100, blank=True)
+    char_field_choice = models.CharField(_("Character Choices"), choices=CompanyType.choices, default=CompanyType.__empty__, max_length=100, blank=True)
+    date_field = models.DateField(_("Date"), null=True, blank=True)
+    datetime_field = models.DateTimeField(_("DateTime"), null=True, blank=True)
+    decimal_field = models.DecimalField(_("Decimal"), max_digits=5, decimal_places=2, null=True)
+    duration_field = models.DurationField(_("Duration"), )
+    email_field = models.EmailField(_("Email"), max_length=254, blank=True)
+    file_field = models.FileField(_("File"), upload_to=file_directory_path, max_length=100)
+    float_field = models.FloatField(_("Float"), null=True)
+    generic_ip_address_field = models.GenericIPAddressField(_("Generic IP"), protocol='both', unpack_ipv4=False, null=True) # 'both', 'IPv4' or 'IPv6'
+    image_field = models.ImageField(_("Image"), upload_to=file_directory_path, height_field=None, width_field=None, max_length=100)
+    integer_field = models.IntegerField(_("Number"), null=True)
+    json_field = models.JSONField(_("JSONField"), default=dict)
+    pos_int_field = models.PositiveIntegerField(_("Positive Integer"), )
+    pos_small_int_field = models.PositiveSmallIntegerField(_("Positive Small Integer"), )
+    slug_field = models.SlugFiels(_("Slug"), max_length=50, blank=True)
+    small_int_field = models.SmallIntegerField(_("Small Integer"), )
+    text_field = models.TextField(_("Text"), blank=True)
+    time_field = models.TimeField(_("Time"), null=True, blank=True)
+    url_field = models.URLField(_("URL"), max_length=200,)
+    uuid_field = models.UUIDField(_("UUID"), default=uuid.uuid4)
+
+    # Relationships
+    # https://docs.djangoproject.com/en/3.1/ref/models/fields/#module-django.db.models.fields.related
+    oto = models.OneToOneField(AA, on_delete=models.CASCADE, null=True, blank=True)
+    fk = models.ForeignKey(BB, on_delete=models.CASCADE, related_name="xxs", null=True, blank=True)
+    mtm = models.ManyToManyField(CC, blank=True)
+
+    # Auto-date fields
+    # https://docs.djangoproject.com/en/3.1/ref/models/fields/#datefield
+    created = models.DateTimeField(_("DateTime Created"), auto_now_add=True, help_text=_("When this item was created"))
+    modified = models.DateTimeField(_("DateTime Modified"), auto_now=True, help_text=_("When this item last updated"))
+
+    # Postgres-specific range fields
+    # https://docs.djangoproject.com/en/3.1/ref/contrib/postgres/fields/
+    integer_range_field = IntegerRangeField(_("IntegerRange"))
+    big_integer_range_field = BigIntegerRangeField(_("BigIntegerRange"))
+    decimal_range_field = DecimalRangeField(_("DecimalRange"))
+    date_time_range_field = DateTimeRangeField(_("DateTimeRange"))
+    date_range_field = DateRangeField(_("DateRange"))
+
+    # GeoDjango fields
+    # https://docs.djangoproject.com/en/3.1/ref/contrib/gis/model-api/
+    point = models.PointField(srid=4326)
+    multi_point = models.MultiPointField()
+    polygon = models.PolygonField()
+    multi_polygon = models.MultiPolygonField()
+    linestring = models.LineStringField()
+    multi_linestring = models.MultiLineStringField()
+    geometry_collection = models.GeometryCollectionField()
+    raster = models.RasterField()
+
+    objects = CombinedMyModelManager()
+
+    class Meta:
+        # https://docs.djangoproject.com/en/3.1/ref/models/options/
+        verbose_name = _("My Model")
+        verbose_name_plural = _("My Models")
+        # abstract = True  # https://docs.djangoproject.com/en/3.1/topics/db/models/#abstract-base-classes
+        # proxy = True  # https://docs.djangoproject.com/en/3.1/topics/db/models/#proxy-models
+
+        db_table = 'my_model'
+
+        # Specifies the default field(s) to use in your model Manager’s latest() and earliest() methods.
+        get_latest_by = ['-datetime_field']
+
+        # The default ordering for the object, for use when obtaining lists of objects:
+        ordering = ['-datetime_field']
+
+        unique_together = [
+            ['char_field', 'slug_field']
+        ]
+        index_together = [
+            ["created", "char_field"],
+        ]
+
+        # https://docs.djangoproject.com/en/3.1/ref/models/indexes/
+        indexes = [
+            models.Index(fields=['char_field', 'text_field']),
+            models.Index(fields=['url_field'], name='url_field_idx'),
+        ]
+
+        # https://docs.djangoproject.com/en/3.1/ref/models/constraints/
+        constraints = [
+            models.CheckConstraint(check=models.Q(integer_field__gte=18), name='integer_gte_18'),
+            models.UniqueConstraint(fields=['created', 'slug_field'], name='unique_slug_created'),
+            models.UniqueConstraint(
+                fields=['fk'],
+                condition=Q(char_field_choice=CompanyType.LIMITED_LIABILITY_PARTNERSHIP),
+                name='unique_llc_for_fk'
+            ),
+        ]
+
+    def __str__(self):
+        # https://docs.djangoproject.com/en/3.1/ref/models/instances/#str
+        return f'{self.char_field} {self.char_field}'
+
+    def save(self, *args, **kwargs):
+        # https://docs.djangoproject.com/en/3.1/topics/db/models/#overriding-model-methods
+        if not self.pk: # this will ensure that the object is new
+            self.slug_field = create_rand_value(
+                app_label=self._meta.app_label,
+                model_name=self.__class__.__name__,
+                prefix="",
+                suffix_len=10
+            )
+        super().save(*args, **kwargs)
+
+    def get_absolute_url(self):
+        # https://docs.djangoproject.com/en/3.1/ref/models/instances/#get-absolute-url
+        from django.urls import reverse
+        return reverse('people.views.details', args=[str(self.id)])
+
+    @property
+    # https://docs.djangoproject.com/en/3.1/glossary/#term-property
+    def char_slug(self):
+        return self.char_field.lower().replace(' ','-')
+
+    def process_invoices(self):
+        do_something()