djangotoolbox / djangotoolbox / fields.py

# All fields except for BlobField written by Jonas Haag <jonas@lophus.org>

from django.db import models
from django.core.exceptions import ValidationError
from django.utils.importlib import import_module

__all__ = ('RawField', 'ListField', 'DictField', 'SetField',
           'BlobField', 'EmbeddedModelField')

EMPTY_ITER = ()

class _HandleAssignment(object):
    """
    A placeholder class that provides a way to set the attribute on the model.
    """
    def __init__(self, field):
        self.field = field

    def __get__(self, obj, type=None):
        if obj is None:
            raise AttributeError('Can only be accessed via an instance.')
        return obj.__dict__[self.field.name]

    def __set__(self, obj, value):
        obj.__dict__[self.field.name] = self.field.to_python(value)

class RawField(models.Field):
    """ Generic field to store anything your database backend allows you to. """
    def get_internal_type(self):
        return 'RawField'

class AbstractIterableField(models.Field):
    """
    Abstract field for fields for storing iterable data type like ``list``,
    ``set`` and ``dict``.

    You can pass an instance of a field as the first argument.
    If you do, the iterable items will be piped through the passed field's
    validation and conversion routines, converting the items to the
    appropriate data type.
    """
    def __init__(self, item_field=None, *args, **kwargs):
        default = kwargs.get('default', None if kwargs.get('null') else EMPTY_ITER)
        if default is not None and not callable(default):
            # ensure a new object is created every time the default is accessed
            kwargs['default'] = lambda: self._type(default)

        super(AbstractIterableField, self).__init__(*args, **kwargs)

        if item_field is None:
            item_field = RawField()
        elif callable(item_field):
            item_field = item_field()
        self.item_field = item_field

    def contribute_to_class(self, cls, name):
        self.item_field.model = cls
        self.item_field.name = name
        super(AbstractIterableField, self).contribute_to_class(cls, name)

        metaclass = getattr(self.item_field, '__metaclass__', None)
        if issubclass(metaclass, models.SubfieldBase):
            setattr(cls, self.name, _HandleAssignment(self))

    @property
    def db_type_prefix(self):
        return self.__class__.__name__

    def db_type(self, connection):
        item_db_type = self.item_field.db_type(connection=connection)
        return '%s:%s' % (self.db_type_prefix, item_db_type)

    def _convert(self, func, values, *args, **kwargs):
        if isinstance(values, (list, tuple, set)):
            return self._type(func(value, *args, **kwargs) for value in values)
        return values

    def to_python(self, value):
        return self._convert(self.item_field.to_python, value)

    def pre_save(self, model_instance, add):
        class fake_instance(object):
            pass
        fake_instance = fake_instance()
        def wrapper(value):
            assert not hasattr(self.item_field, 'attname')
            fake_instance.value = value
            self.item_field.attname = 'value'
            try:
                return self.item_field.pre_save(fake_instance, add)
            finally:
                del self.item_field.attname

        return self._convert(wrapper, getattr(model_instance, self.attname))

    def get_db_prep_value(self, value, connection, prepared=False):
        return self._convert(self.item_field.get_db_prep_value, value,
                             connection=connection, prepared=prepared)

    def get_db_prep_save(self, value, connection):
        return self._convert(self.item_field.get_db_prep_save,
                             value, connection=connection)

    def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
        # TODO/XXX: Remove as_lookup_value() once we have a cleaner solution
        # for dot-notation queries
        if hasattr(value, 'as_lookup_value'):
            value = value.as_lookup_value(self, lookup_type, connection)

        return self.item_field.get_db_prep_lookup(lookup_type, value,
            connection=connection, prepared=prepared)

    def validate(self, values, model_instance):
        try:
            iter(values)
        except TypeError:
            raise ValidationError('Value of type %r is not iterable' % type(values))

    def formfield(self, **kwargs):
        raise NotImplementedError('No form field implemented for %r' % type(self))

class ListField(AbstractIterableField):
    """
    Field representing a Python ``list``.

    If the optional keyword argument `ordering` is given, it must be a callable
    that is passed to :meth:`list.sort` as `key` argument. If `ordering` is
    given, the items in the list will be sorted before sending them to the
    database.
    """
    _type = list
    db_type_prefix = 'ListField'

    def __init__(self, *args, **kwargs):
        self.ordering = kwargs.pop('ordering', None)
        if self.ordering is not None and not callable(self.ordering):
            raise TypeError("'ordering' has to be a callable or None, "
                            "not of type %r" %  type(self.ordering))
        super(ListField, self).__init__(*args, **kwargs)

    def pre_save(self, model_instance, add):
        values = getattr(model_instance, self.attname)
        if values is None:
            return None
        if values and self.ordering:
            values.sort(key=self.ordering)
        return super(ListField, self).pre_save(model_instance, add)

class SetField(AbstractIterableField):
    """
    Field representing a Python ``set``.
    """
    _type = set
    db_type_prefix = 'SetField'

class DictField(AbstractIterableField):
    """
    Field representing a Python ``dict``.

    The field type conversions described in :class:`AbstractIterableField`
    only affect values of the dictionary, not keys.

    Depending on the backend, keys that aren't strings might not be allowed.
    """
    _type = dict
    db_type_prefix = 'DictField'

    def _convert(self, func, values, *args, **kwargs):
        if values is None:
            return None
        return dict((key, func(value, *args, **kwargs))
                     for key, value in values.iteritems())

    def validate(self, values, model_instance):
        if not isinstance(values, dict):
            raise ValidationError('Value is of type %r. Should be a dict.' % type(values))

class BlobField(models.Field):
    """
    A field for storing blobs of binary data.

    The value might either be a string (or something that can be converted to
    a string), or a file-like object.

    In the latter case, the object has to provide a ``read`` method from which
    the blob is read.
    """
    def get_internal_type(self):
        return 'BlobField'

    def formfield(self, **kwargs):
        # A file widget is provided, but use model FileField or ImageField
        # for storing specific files most of the time
        from .widgets import BlobWidget
        from django.forms import FileField
        defaults = {'form_class': FileField, 'widget': BlobWidget}
        defaults.update(kwargs)
        return super(BlobField, self).formfield(**defaults)

    def get_db_prep_value(self, value, connection, prepared=False):
        if hasattr(value, 'read'):
            return value.read()
        else:
            return str(value)

    def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
        raise TypeError("BlobFields do not support lookups")

    def value_to_string(self, obj):
        return str(self._get_val_from_obj(obj))

class EmbeddedModelField(models.Field):
    """
    Field that allows you to embed a model instance.

    :param model: (optional) The model class that shall be embedded
                  (may also be passed as string similar to relation fields)
    """
    __metaclass__ = models.SubfieldBase

    def __init__(self, model=None, *args, **kwargs):
        self.embedded_model = model
        kwargs.setdefault('default', None)
        super(EmbeddedModelField, self).__init__(*args, **kwargs)

    def db_type(self, connection):
        return 'DictField:RawField'

    def _set_model(self, model):
        # We need to know the model to generate a valid key for the lookup but
        # EmbeddedModelFields are not contributed_to_class if used in ListFields
        # (and friends), so we can only know the model when the ListField sets
        # our 'model' attribute in its contribute_to_class method.

        if model is not None and isinstance(self.embedded_model, basestring):
            # The model argument passed to __init__ was a string, so we need
            # to make sure to resolve that string to the corresponding model
            # class, similar to relation fields. We abuse some of the relation
            # fields' code to do the lookup here:
            def _resolve_lookup(self_, resolved_model, model):
                self.embedded_model = resolved_model
            from django.db.models.fields.related import add_lazy_relation
            add_lazy_relation(model, self, self.embedded_model, _resolve_lookup)

        self._model = model

    model = property(lambda self:self._model, _set_model)

    def pre_save(self, model_instance, _):
        embedded_instance = getattr(model_instance, self.attname)
        if embedded_instance is None:
            return None, None

        model = self.embedded_model or models.Model
        if not isinstance(embedded_instance, model):
            raise TypeError("Expected instance of type %r, not %r"
                            % (model, type(embedded_instance)))

        values = []
        for field in embedded_instance._meta.fields:
            add = not embedded_instance._entity_exists
            value = field.pre_save(embedded_instance, add)
            if field.primary_key and value is None:
                # exclude unset pks ({"id" : None})
                continue
            values.append((field, value))

        return embedded_instance, values

    def get_db_prep_value(self, (embedded_instance, value_list), **kwargs):
        if value_list is None:
            return None
        values = dict((field.column, field.get_db_prep_value(value, **kwargs))
                      for field, value in value_list)
        if self.embedded_model is None:
            values.update({'_module' : embedded_instance.__class__.__module__,
                           '_model'  : embedded_instance.__class__.__name__})
        # This instance will exist in the db very soon.
        embedded_instance._entity_exists = True
        return values

    # TODO/XXX: Remove this once we have a cleaner solution
    def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
        if hasattr(value, 'as_lookup_value'):
            value = value.as_lookup_value(self, lookup_type, connection)
        return value

    def to_python(self, values):
        if not isinstance(values, dict):
            return values

        module, model = values.pop('_module', None), values.pop('_model', None)
        if module is not None:
            model = getattr(import_module(module), model)
        else:
            model = self.embedded_model

        data = {}
        for field in model._meta.fields:
            try:
                # TODO/XXX: str(...) is a workaround for old Python releases.
                # Remove this someday.
                data[str(field.attname)] = values[field.column]
            except KeyError:
                pass
        return model(__entity_exists=True, **data)
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