Python django.db.models.expressions.Expression() Examples

def process_rhs(self, compiler, connection):
        rhs, rhs_params = super(GISLookup, self).process_rhs(compiler, connection)
        if hasattr(self.rhs, '_as_sql'):
            # If rhs is some QuerySet, don't touch it
            return rhs, rhs_params

        geom = self.rhs
        if isinstance(self.rhs, Col):
            # Make sure the F Expression destination field exists, and
            # set an `srid` attribute with the same as that of the
            # destination.
            geo_fld = self.rhs.output_field
            if not hasattr(geo_fld, 'srid'):
                raise ValueError('No geographic field found in expression.')
            self.rhs.srid = geo_fld.srid
        elif isinstance(self.rhs, Expression):
            raise ValueError('Complex expressions not supported for GeometryField')
        elif isinstance(self.rhs, (list, tuple)):
            geom = self.rhs[0]
        rhs = connection.ops.get_geom_placeholder(self.lhs.output_field, geom, compiler)
        return rhs, rhs_params 

def process_rhs(self, compiler, connection):
        rhs, rhs_params = super(GISLookup, self).process_rhs(compiler, connection)
        if hasattr(self.rhs, '_as_sql'):
            # If rhs is some QuerySet, don't touch it
            return rhs, rhs_params

        geom = self.rhs
        if isinstance(self.rhs, Col):
            # Make sure the F Expression destination field exists, and
            # set an `srid` attribute with the same as that of the
            # destination.
            geo_fld = self.rhs.output_field
            if not hasattr(geo_fld, 'srid'):
                raise ValueError('No geographic field found in expression.')
            self.rhs.srid = geo_fld.srid
        elif isinstance(self.rhs, Expression):
            raise ValueError('Complex expressions not supported for GeometryField')
        elif isinstance(self.rhs, (list, tuple)):
            geom = self.rhs[0]
        rhs = connection.ops.get_geom_placeholder(self.lhs.output_field, geom, compiler)
        return rhs, rhs_params 

def get_prep_value(self, value):
        """Override the base class so it doesn't cast all values to strings.

        psqlextra supports expressions in hstore fields, so casting all
        values to strings is a bad idea.
        """

        value = Field.get_prep_value(self, value)

        if isinstance(value, dict):
            prep_value = {}
            for key, val in value.items():
                if isinstance(val, Expression):
                    prep_value[key] = val
                elif val is not None:
                    prep_value[key] = str(val)
                else:
                    prep_value[key] = val

            value = prep_value

        if isinstance(value, list):
            value = [str(item) for item in value]

        return value 

def get_prep_value(self, value):
        """
        Spatial lookup values are either a parameter that is (or may be
        converted to) a geometry, or a sequence of lookup values that
        begins with a geometry.  This routine will setup the geometry
        value properly, and preserve any other lookup parameters before
        returning to the caller.
        """
        value = super(GeometryField, self).get_prep_value(value)
        if isinstance(value, Expression):
            return value
        elif isinstance(value, (tuple, list)):
            geom = value[0]
            seq_value = True
        else:
            geom = value
            seq_value = False

        # When the input is not a GEOS geometry, attempt to construct one
        # from the given string input.
        if isinstance(geom, Geometry):
            pass
        elif isinstance(geom, (bytes, six.string_types)) or hasattr(geom, '__geo_interface__'):
            try:
                geom = Geometry(geom)
            except GeometryException:
                raise ValueError('Could not create geometry from lookup value.')
        else:
            raise ValueError('Cannot use object with type %s for a geometry lookup parameter.' % type(geom).__name__)

        # Assigning the SRID value.
        geom.srid = self.get_srid(geom)

        if seq_value:
            lookup_val = [geom]
            lookup_val.extend(value[1:])
            return tuple(lookup_val)
        else:
            return geom 

def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
        """
        Prepare for the database lookup, and return any spatial parameters
        necessary for the query.  This includes wrapping any geometry
        parameters with a backend-specific adapter and formatting any distance
        parameters into the correct units for the coordinate system of the
        field.
        """
        # special case for isnull lookup
        if lookup_type == 'isnull':
            return []
        elif lookup_type in self.class_lookups:
            # Populating the parameters list, and wrapping the Geometry
            # with the Adapter of the spatial backend.
            if isinstance(value, (tuple, list)):
                params = [connection.ops.Adapter(value[0])]
                if self.class_lookups[lookup_type].distance:
                    # Getting the distance parameter in the units of the field.
                    params += self.get_distance(value[1:], lookup_type, connection)
                elif lookup_type in connection.ops.truncate_params:
                    # Lookup is one where SQL parameters aren't needed from the
                    # given lookup value.
                    pass
                else:
                    params += value[1:]
            elif isinstance(value, Expression):
                params = []
            else:
                params = [connection.ops.Adapter(value)]

            return params
        else:
            raise ValueError('%s is not a valid spatial lookup for %s.' %
                             (lookup_type, self.__class__.__name__)) 

def get_prep_value(self, value):
        """
        Spatial lookup values are either a parameter that is (or may be
        converted to) a geometry, or a sequence of lookup values that
        begins with a geometry.  This routine will setup the geometry
        value properly, and preserve any other lookup parameters before
        returning to the caller.
        """
        value = super(GeometryField, self).get_prep_value(value)
        if isinstance(value, Expression):
            return value
        elif isinstance(value, (tuple, list)):
            geom = value[0]
            seq_value = True
        else:
            geom = value
            seq_value = False

        # When the input is not a GEOS geometry, attempt to construct one
        # from the given string input.
        if isinstance(geom, Geometry):
            pass
        elif isinstance(geom, (bytes, six.string_types)) or hasattr(geom, '__geo_interface__'):
            try:
                geom = Geometry(geom)
            except GeometryException:
                raise ValueError('Could not create geometry from lookup value.')
        else:
            raise ValueError('Cannot use object with type %s for a geometry lookup parameter.' % type(geom).__name__)

        # Assigning the SRID value.
        geom.srid = self.get_srid(geom)

        if seq_value:
            lookup_val = [geom]
            lookup_val.extend(value[1:])
            return tuple(lookup_val)
        else:
            return geom 

def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
        """
        Prepare for the database lookup, and return any spatial parameters
        necessary for the query.  This includes wrapping any geometry
        parameters with a backend-specific adapter and formatting any distance
        parameters into the correct units for the coordinate system of the
        field.
        """
        # special case for isnull lookup
        if lookup_type == 'isnull':
            return []
        elif lookup_type in self.class_lookups:
            # Populating the parameters list, and wrapping the Geometry
            # with the Adapter of the spatial backend.
            if isinstance(value, (tuple, list)):
                params = [connection.ops.Adapter(value[0])]
                if self.class_lookups[lookup_type].distance:
                    # Getting the distance parameter in the units of the field.
                    params += self.get_distance(value[1:], lookup_type, connection)
                elif lookup_type in connection.ops.truncate_params:
                    # Lookup is one where SQL parameters aren't needed from the
                    # given lookup value.
                    pass
                else:
                    params += value[1:]
            elif isinstance(value, Expression):
                params = []
            else:
                params = [connection.ops.Adapter(value)]

            return params
        else:
            raise ValueError('%s is not a valid spatial lookup for %s.' %
                             (lookup_type, self.__class__.__name__)) 

def resolve_field(model_field, lookup_expr):
    """
    Resolves a ``lookup_expr`` into its final output field, given
    the initial ``model_field``. The lookup expression should only contain
    transforms and lookups, not intermediary model field parts.

    Note:
    This method is based on django.db.models.sql.query.Query.build_lookup

    For more info on the lookup API:
    https://docs.djangoproject.com/en/1.9/ref/models/lookups/

    """
    query = model_field.model._default_manager.all().query
    lhs = Expression(model_field)
    lookups = lookup_expr.split(LOOKUP_SEP)

    assert len(lookups) > 0

    try:
        while lookups:
            name = lookups[0]
            args = (lhs, name)
            if django.VERSION < (2, 0):
                # rest_of_lookups was removed in Django 2.0
                args += (lookups,)
            # If there is just one part left, try first get_lookup() so
            # that if the lhs supports both transform and lookup for the
            # name, then lookup will be picked.
            if len(lookups) == 1:
                final_lookup = lhs.get_lookup(name)
                if not final_lookup:
                    # We didn't find a lookup. We are going to interpret
                    # the name as transform, and do an Exact lookup against
                    # it.
                    lhs = query.try_transform(*args)
                    final_lookup = lhs.get_lookup('exact')
                return lhs.output_field, final_lookup.lookup_name
            lhs = query.try_transform(*args)
            lookups = lookups[1:]
    except FieldError as e:
        six.raise_from(FieldLookupError(model_field, lookup_expr), e)