Python django.db.models.Field() Examples

def value_to_string(self, obj):
        """
        We need to support both legacy `_get_val_from_obj` and new `value_from_object` models.Field methods.
        It would be better to wrap it with try -> except AttributeError -> fallback to legacy.
        Unfortunately, we can catch AttributeError exception from `value_from_object` function itself.
        Parsing exception string is an overkill here, that's why we check for attribute existence

        :param obj: Value to serialize

        :return: Serialized value
        """

        if hasattr(self, 'value_from_object'):
            value = self.value_from_object(obj)
        else:  # fallback for legacy django versions
            value = self._get_val_from_obj(obj)

        return self.get_prep_value(value) 

def test_db_tablespace(self):
        field = models.Field()
        _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {})
        # With a DEFAULT_DB_TABLESPACE.
        with self.settings(DEFAULT_DB_TABLESPACE='foo'):
            _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {})
        # With a db_tablespace.
        field = models.Field(db_tablespace='foo')
        _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {'db_tablespace': 'foo'})
        # With a db_tablespace equal to DEFAULT_DB_TABLESPACE.
        with self.settings(DEFAULT_DB_TABLESPACE='foo'):
            _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {'db_tablespace': 'foo'}) 

def _check_date_hierarchy(self, obj):
        """ Check that date_hierarchy refers to DateField or DateTimeField. """

        if obj.date_hierarchy is None:
            return []
        else:
            try:
                field = get_fields_from_path(obj.model, obj.date_hierarchy)[-1]
            except (NotRelationField, FieldDoesNotExist):
                return [
                    checks.Error(
                        "The value of 'date_hierarchy' refers to '%s', which "
                        "does not refer to a Field." % obj.date_hierarchy,
                        obj=obj.__class__,
                        id='admin.E127',
                    )
                ]
            else:
                if not isinstance(field, (models.DateField, models.DateTimeField)):
                    return must_be('a DateField or DateTimeField', option='date_hierarchy', obj=obj, id='admin.E128')
                else:
                    return [] 

def test_user_specified_details(self):
        class MyField(models.Field):
            system_check_removed_details = {
                'msg': 'Support for this field is gone.',
                'hint': 'Use something else.',
                'id': 'fields.E999',
            }

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Error(
                msg='Support for this field is gone.',
                hint='Use something else.',
                obj=Model._meta.get_field('name'),
                id='fields.E999',
            )
        ]) 

def test_user_specified_details(self):
        class MyField(models.Field):
            system_check_deprecated_details = {
                'msg': 'This field is deprecated and will be removed soon.',
                'hint': 'Use something else.',
                'id': 'fields.W999',
            }

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Warning(
                msg='This field is deprecated and will be removed soon.',
                hint='Use something else.',
                obj=Model._meta.get_field('name'),
                id='fields.W999',
            )
        ]) 

def _check_date_hierarchy(self, obj):
        """ Check that date_hierarchy refers to DateField or DateTimeField. """

        if obj.date_hierarchy is None:
            return []
        else:
            try:
                field = get_fields_from_path(obj.model, obj.date_hierarchy)[-1]
            except (NotRelationField, FieldDoesNotExist):
                return [
                    checks.Error(
                        "The value of 'date_hierarchy' refers to '%s', which "
                        "does not refer to a Field." % obj.date_hierarchy,
                        obj=obj.__class__,
                        id='admin.E127',
                    )
                ]
            else:
                if not isinstance(field, (models.DateField, models.DateTimeField)):
                    return must_be('a DateField or DateTimeField', option='date_hierarchy', obj=obj, id='admin.E128')
                else:
                    return [] 

def try_dbfield(fn, field_class):
    """
    Try ``fn`` with the DB ``field_class`` by walking its
    MRO until a result is found.

    ex::
        _try_dbfield(field_dict.get, models.CharField)

    """
    # walk the mro, as field_class could be a derived model field.
    for cls in field_class.mro():
        # skip if cls is models.Field
        if cls is models.Field:
            continue

        data = fn(cls)
        if data:
            return data 

def _check_date_hierarchy(self, obj):
        """ Check that date_hierarchy refers to DateField or DateTimeField. """

        if obj.date_hierarchy is None:
            return []
        else:
            try:
                field = get_fields_from_path(obj.model, obj.date_hierarchy)[-1]
            except (NotRelationField, FieldDoesNotExist):
                return [
                    checks.Error(
                        "The value of 'date_hierarchy' refers to '%s', which "
                        "does not refer to a Field." % obj.date_hierarchy,
                        obj=obj.__class__,
                        id='admin.E127',
                    )
                ]
            else:
                if not isinstance(field, (models.DateField, models.DateTimeField)):
                    return must_be('a DateField or DateTimeField', option='date_hierarchy', obj=obj, id='admin.E128')
                else:
                    return [] 

def _get_declared_fields(cls, bases, attrs):
        fields = [(field_name, attrs.pop(field_name))
                  for field_name, obj in list(attrs.items())
                  if isinstance(obj, Field)]
        fields.sort(key=lambda x: x[1]._creation_counter)

        # If this class is subclassing another Serializer, add that Serializer's
        # fields.  Note that we loop over the bases in *reverse*. This is necessary
        # in order to maintain the correct order of fields.
        for base in reversed(bases):
            if hasattr(base, '_declared_fields'):
                fields = [
                    (field_name, obj) for field_name, obj
                    in base._declared_fields.items()
                    if field_name not in attrs
                ] + fields

        return OrderedDict(fields) 

def _check_date_hierarchy(self, obj):
        """ Check that date_hierarchy refers to DateField or DateTimeField. """

        if obj.date_hierarchy is None:
            return []
        else:
            try:
                field = get_fields_from_path(obj.model, obj.date_hierarchy)[-1]
            except (NotRelationField, FieldDoesNotExist):
                return [
                    checks.Error(
                        "The value of 'date_hierarchy' refers to '%s', which "
                        "does not refer to a Field." % obj.date_hierarchy,
                        obj=obj.__class__,
                        id='admin.E127',
                    )
                ]
            else:
                if not isinstance(field, (models.DateField, models.DateTimeField)):
                    return must_be('a DateField or DateTimeField', option='date_hierarchy', obj=obj, id='admin.E128')
                else:
                    return [] 

def test_user_specified_details(self):
        class MyField(models.Field):
            system_check_removed_details = {
                'msg': 'Support for this field is gone.',
                'hint': 'Use something else.',
                'id': 'fields.E999',
            }

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Error(
                msg='Support for this field is gone.',
                hint='Use something else.',
                obj=Model._meta.get_field('name'),
                id='fields.E999',
            )
        ]) 

def encrypt(base_field, key=None, ttl=None):
    """
    A decorator for creating encrypted model fields.

    :type base_field: models.Field[T]
    :param bytes key: This is an optional argument.

        Allows for specifying an instance specific encryption key.
    :param int ttl: This is an optional argument.

        The amount of time in seconds that a value can be stored for. If the
        time to live of the data has passed, it will become unreadable.
        The expired value will return an :class:`Expired` object.
    :rtype: models.Field[EncryptedMixin, T]
    """
    if not isinstance(base_field, models.Field):
        assert key is None
        assert ttl is None
        return get_encrypted_field(base_field)

    name, path, args, kwargs = base_field.deconstruct()
    kwargs.update({'key': key, 'ttl': ttl})
    return get_encrypted_field(type(base_field))(*args, **kwargs) 

def get_encrypted_field(base_class):
    """
    A get or create method for encrypted fields, we cache the field in
    the module to avoid recreation. This also allows us to always return
    the same class reference for a field.

    :type base_class: models.Field[T]
    :rtype: models.Field[EncryptedMixin, T]
    """
    assert not isinstance(base_class, models.Field)
    field_name = 'Encrypted' + base_class.__name__
    if base_class not in FIELD_CACHE:
        FIELD_CACHE[base_class] = type(field_name,
                                       (EncryptedMixin, base_class), {
                                           'base_class': base_class,
                                       })
    return FIELD_CACHE[base_class] 

def test_db_tablespace(self):
        field = models.Field()
        _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {})
        # With a DEFAULT_DB_TABLESPACE.
        with self.settings(DEFAULT_DB_TABLESPACE='foo'):
            _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {})
        # With a db_tablespace.
        field = models.Field(db_tablespace='foo')
        _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {'db_tablespace': 'foo'})
        # With a db_tablespace equal to DEFAULT_DB_TABLESPACE.
        with self.settings(DEFAULT_DB_TABLESPACE='foo'):
            _, _, args, kwargs = field.deconstruct()
        self.assertEqual(args, [])
        self.assertEqual(kwargs, {'db_tablespace': 'foo'}) 

def test_model_docstring_renders_correctly(self):
        summary = (
            '<h2 class="subhead"><p>Stores information about a person, related to <a class="reference external" '
            'href="/admindocs/models/myapp.company/">myapp.Company</a>.</p></h2>'
        )
        subheading = '<p><strong>Notes</strong></p>'
        body = '<p>Use <tt class="docutils literal">save_changes()</tt> when saving this object.</p>'
        model_body = (
            '<dl class="docutils"><dt><tt class="'
            'docutils literal">company</tt></dt><dd>Field storing <a class="'
            'reference external" href="/admindocs/models/myapp.company/">'
            'myapp.Company</a> where the person works.</dd></dl>'
        )
        self.assertContains(self.response, 'DESCRIPTION')
        self.assertContains(self.response, summary, html=True)
        self.assertContains(self.response, subheading, html=True)
        self.assertContains(self.response, body, html=True)
        self.assertContains(self.response, model_body, html=True) 

def _is_hstore_field(
        self, field_name: str
    ) -> Tuple[bool, Optional[models.Field]]:
        """Gets whether the field with the specified name is a HStoreField.

        Returns     A tuple of a boolean indicating whether the field
        with the specified name is a HStoreField, and the     field
        instance.
        """

        field_instance = None
        for field in self.model._meta.local_concrete_fields:
            if field.name == field_name or field.column == field_name:
                field_instance = field
                break

        return isinstance(field_instance, HStoreField), field_instance 

def deep_deconstruct(self, obj):
        """
        Recursive deconstruction for a field and its arguments.
        Used for full comparison for rename/alter; sometimes a single-level
        deconstruction will not compare correctly.
        """
        if not hasattr(obj, 'deconstruct') or isinstance(obj, type):
            return obj
        deconstructed = obj.deconstruct()
        if isinstance(obj, models.Field):
            # we have a field which also returns a name
            deconstructed = deconstructed[1:]
        path, args, kwargs = deconstructed
        return (
            path,
            [self.deep_deconstruct(value) for value in args],
            {
                key: self.deep_deconstruct(value)
                for key, value in kwargs.items()
            },
        ) 

def build_unknown_field(self, field_name, model_class):
        """
        Raise an error on any unknown fields.
        """
        raise ImproperlyConfigured(
            'Field name `%s` is not valid for model `%s`.' %
            (field_name, model_class.__name__)
        ) 

def test_default_details(self):
        class MyField(models.Field):
            system_check_deprecated_details = {}

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Warning(
                msg='MyField has been deprecated.',
                obj=Model._meta.get_field('name'),
                id='fields.WXXX',
            )
        ]) 

def test_deconstruct_nested_field(self):
        """deconstruct() uses __qualname__ for nested class support."""
        name, path, args, kwargs = Nested.Field().deconstruct()
        self.assertEqual(path, 'model_fields.tests.Nested.Field') 

def test_default_details(self):
        class MyField(models.Field):
            system_check_removed_details = {}

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Error(
                msg='MyField has been removed except for support in historical migrations.',
                obj=Model._meta.get_field('name'),
                id='fields.EXXX',
            )
        ]) 

def test_custom_fields(self):
        self.assertEqual(views.get_readable_field_data_type(CustomField()), 'A custom field type')
        self.assertEqual(
            views.get_readable_field_data_type(DescriptionLackingField()),
            'Field of type: DescriptionLackingField'
        ) 

def test_field_instance_is_picklable(self):
        """Field instances can be pickled."""
        field = models.Field(max_length=100, default='a string')
        # Must be picklable with this cached property populated (#28188).
        field._get_default
        pickle.dumps(field) 

def test_show_hidden_initial(self):
        """
        Fields with choices respect show_hidden_initial as a kwarg to
        formfield().
        """
        choices = [(0, 0), (1, 1)]
        model_field = models.Field(choices=choices)
        form_field = model_field.formfield(show_hidden_initial=True)
        self.assertTrue(form_field.show_hidden_initial)

        form_field = model_field.formfield(show_hidden_initial=False)
        self.assertFalse(form_field.show_hidden_initial) 

def test_default_details(self):
        class MyField(models.Field):
            system_check_removed_details = {}

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Error(
                msg='MyField has been removed except for support in historical migrations.',
                obj=Model._meta.get_field('name'),
                id='fields.EXXX',
            )
        ]) 

def test_default_details(self):
        class MyField(models.Field):
            system_check_deprecated_details = {}

        class Model(models.Model):
            name = MyField()

        model = Model()
        self.assertEqual(model.check(), [
            checks.Warning(
                msg='MyField has been deprecated.',
                obj=Model._meta.get_field('name'),
                id='fields.WXXX',
            )
        ]) 

def test_choices_form_class(self):
        """Can supply a custom choices form class to Field.formfield()"""
        choices = [('a', 'a')]
        field = models.CharField(choices=choices)
        klass = forms.TypedMultipleChoiceField
        self.assertIsInstance(field.formfield(choices_form_class=klass), klass) 

def test_choices_form_class(self):
        """Can supply a custom choices form class to Field.formfield()"""
        choices = [('a', 'a')]
        field = models.CharField(choices=choices)
        klass = forms.TypedMultipleChoiceField
        self.assertIsInstance(field.formfield(choices_form_class=klass), klass) 

def _get_field(field_name: str, model: models.Model) -> Optional[models.Field]:
        try:
            # noinspection PyProtectedMember
            return model._meta.get_field(field_name)
        except models.FieldDoesNotExist:
            return None 

def deep_deconstruct(self, obj):
        """
        Recursive deconstruction for a field and its arguments.
        Used for full comparison for rename/alter; sometimes a single-level
        deconstruction will not compare correctly.
        """
        if isinstance(obj, list):
            return [self.deep_deconstruct(value) for value in obj]
        elif isinstance(obj, tuple):
            return tuple(self.deep_deconstruct(value) for value in obj)
        elif isinstance(obj, dict):
            return {
                key: self.deep_deconstruct(value)
                for key, value in obj.items()
            }
        elif isinstance(obj, functools.partial):
            return (obj.func, self.deep_deconstruct(obj.args), self.deep_deconstruct(obj.keywords))
        elif isinstance(obj, COMPILED_REGEX_TYPE):
            return RegexObject(obj)
        elif isinstance(obj, type):
            # If this is a type that implements 'deconstruct' as an instance method,
            # avoid treating this as being deconstructible itself - see #22951
            return obj
        elif hasattr(obj, 'deconstruct'):
            deconstructed = obj.deconstruct()
            if isinstance(obj, models.Field):
                # we have a field which also returns a name
                deconstructed = deconstructed[1:]
            path, args, kwargs = deconstructed
            return (
                path,
                [self.deep_deconstruct(value) for value in args],
                {
                    key: self.deep_deconstruct(value)
                    for key, value in kwargs.items()
                },
            )
        else:
            return obj