280 lines
9.2 KiB
Python
280 lines
9.2 KiB
Python
"""
|
|
Various data structures used in query construction.
|
|
|
|
Factored out from django.db.models.query to avoid making the main module very
|
|
large and/or so that they can be used by other modules without getting into
|
|
circular import difficulties.
|
|
"""
|
|
|
|
import weakref
|
|
from django.utils.copycompat import deepcopy
|
|
|
|
from django.db.backends import util
|
|
from django.utils import tree
|
|
from django.utils.datastructures import SortedDict
|
|
|
|
|
|
class CyclicDependency(Exception):
|
|
"""
|
|
An error when dealing with a collection of objects that have a cyclic
|
|
dependency, i.e. when deleting multiple objects.
|
|
"""
|
|
pass
|
|
|
|
class InvalidQuery(Exception):
|
|
"""
|
|
The query passed to raw isn't a safe query to use with raw.
|
|
"""
|
|
pass
|
|
|
|
|
|
class CollectedObjects(object):
|
|
"""
|
|
A container that stores keys and lists of values along with remembering the
|
|
parent objects for all the keys.
|
|
|
|
This is used for the database object deletion routines so that we can
|
|
calculate the 'leaf' objects which should be deleted first.
|
|
|
|
previously_seen is an optional argument. It must be a CollectedObjects
|
|
instance itself; any previously_seen collected object will be blocked from
|
|
being added to this instance.
|
|
"""
|
|
|
|
def __init__(self, previously_seen=None):
|
|
self.data = {}
|
|
self.children = {}
|
|
if previously_seen:
|
|
self.blocked = previously_seen.blocked
|
|
for cls, seen in previously_seen.data.items():
|
|
self.blocked.setdefault(cls, SortedDict()).update(seen)
|
|
else:
|
|
self.blocked = {}
|
|
|
|
def add(self, model, pk, obj, parent_model, parent_obj=None, nullable=False):
|
|
"""
|
|
Adds an item to the container.
|
|
|
|
Arguments:
|
|
* model - the class of the object being added.
|
|
* pk - the primary key.
|
|
* obj - the object itself.
|
|
* parent_model - the model of the parent object that this object was
|
|
reached through.
|
|
* parent_obj - the parent object this object was reached
|
|
through (not used here, but needed in the API for use elsewhere)
|
|
* nullable - should be True if this relation is nullable.
|
|
|
|
Returns True if the item already existed in the structure and
|
|
False otherwise.
|
|
"""
|
|
if pk in self.blocked.get(model, {}):
|
|
return True
|
|
|
|
d = self.data.setdefault(model, SortedDict())
|
|
retval = pk in d
|
|
d[pk] = obj
|
|
# Nullable relationships can be ignored -- they are nulled out before
|
|
# deleting, and therefore do not affect the order in which objects
|
|
# have to be deleted.
|
|
if parent_model is not None and not nullable:
|
|
self.children.setdefault(parent_model, []).append(model)
|
|
return retval
|
|
|
|
def __contains__(self, key):
|
|
return self.data.__contains__(key)
|
|
|
|
def __getitem__(self, key):
|
|
return self.data[key]
|
|
|
|
def __nonzero__(self):
|
|
return bool(self.data)
|
|
|
|
def iteritems(self):
|
|
for k in self.ordered_keys():
|
|
yield k, self[k]
|
|
|
|
def items(self):
|
|
return list(self.iteritems())
|
|
|
|
def keys(self):
|
|
return self.ordered_keys()
|
|
|
|
def ordered_keys(self):
|
|
"""
|
|
Returns the models in the order that they should be dealt with (i.e.
|
|
models with no dependencies first).
|
|
"""
|
|
dealt_with = SortedDict()
|
|
# Start with items that have no children
|
|
models = self.data.keys()
|
|
while len(dealt_with) < len(models):
|
|
found = False
|
|
for model in models:
|
|
if model in dealt_with:
|
|
continue
|
|
children = self.children.setdefault(model, [])
|
|
if len([c for c in children if c not in dealt_with]) == 0:
|
|
dealt_with[model] = None
|
|
found = True
|
|
if not found:
|
|
raise CyclicDependency(
|
|
"There is a cyclic dependency of items to be processed.")
|
|
|
|
return dealt_with.keys()
|
|
|
|
def unordered_keys(self):
|
|
"""
|
|
Fallback for the case where is a cyclic dependency but we don't care.
|
|
"""
|
|
return self.data.keys()
|
|
|
|
class QueryWrapper(object):
|
|
"""
|
|
A type that indicates the contents are an SQL fragment and the associate
|
|
parameters. Can be used to pass opaque data to a where-clause, for example.
|
|
"""
|
|
def __init__(self, sql, params):
|
|
self.data = sql, params
|
|
|
|
def as_sql(self, qn=None, connection=None):
|
|
return self.data
|
|
|
|
class Q(tree.Node):
|
|
"""
|
|
Encapsulates filters as objects that can then be combined logically (using
|
|
& and |).
|
|
"""
|
|
# Connection types
|
|
AND = 'AND'
|
|
OR = 'OR'
|
|
default = AND
|
|
|
|
def __init__(self, *args, **kwargs):
|
|
super(Q, self).__init__(children=list(args) + kwargs.items())
|
|
|
|
def _combine(self, other, conn):
|
|
if not isinstance(other, Q):
|
|
raise TypeError(other)
|
|
obj = type(self)()
|
|
obj.add(self, conn)
|
|
obj.add(other, conn)
|
|
return obj
|
|
|
|
def __or__(self, other):
|
|
return self._combine(other, self.OR)
|
|
|
|
def __and__(self, other):
|
|
return self._combine(other, self.AND)
|
|
|
|
def __invert__(self):
|
|
obj = type(self)()
|
|
obj.add(self, self.AND)
|
|
obj.negate()
|
|
return obj
|
|
|
|
class DeferredAttribute(object):
|
|
"""
|
|
A wrapper for a deferred-loading field. When the value is read from this
|
|
object the first time, the query is executed.
|
|
"""
|
|
def __init__(self, field_name, model):
|
|
self.field_name = field_name
|
|
self.model_ref = weakref.ref(model)
|
|
self.loaded = False
|
|
|
|
def __get__(self, instance, owner):
|
|
"""
|
|
Retrieves and caches the value from the datastore on the first lookup.
|
|
Returns the cached value.
|
|
"""
|
|
from django.db.models.fields import FieldDoesNotExist
|
|
|
|
assert instance is not None
|
|
cls = self.model_ref()
|
|
data = instance.__dict__
|
|
if data.get(self.field_name, self) is self:
|
|
# self.field_name is the attname of the field, but only() takes the
|
|
# actual name, so we need to translate it here.
|
|
try:
|
|
cls._meta.get_field_by_name(self.field_name)
|
|
name = self.field_name
|
|
except FieldDoesNotExist:
|
|
name = [f.name for f in cls._meta.fields
|
|
if f.attname == self.field_name][0]
|
|
# We use only() instead of values() here because we want the
|
|
# various data coersion methods (to_python(), etc.) to be called
|
|
# here.
|
|
val = getattr(
|
|
cls._base_manager.filter(pk=instance.pk).only(name).using(
|
|
instance._state.db).get(),
|
|
self.field_name
|
|
)
|
|
data[self.field_name] = val
|
|
return data[self.field_name]
|
|
|
|
def __set__(self, instance, value):
|
|
"""
|
|
Deferred loading attributes can be set normally (which means there will
|
|
never be a database lookup involved.
|
|
"""
|
|
instance.__dict__[self.field_name] = value
|
|
|
|
def select_related_descend(field, restricted, requested, reverse=False):
|
|
"""
|
|
Returns True if this field should be used to descend deeper for
|
|
select_related() purposes. Used by both the query construction code
|
|
(sql.query.fill_related_selections()) and the model instance creation code
|
|
(query.get_cached_row()).
|
|
|
|
Arguments:
|
|
* field - the field to be checked
|
|
* restricted - a boolean field, indicating if the field list has been
|
|
manually restricted using a requested clause)
|
|
* requested - The select_related() dictionary.
|
|
* reverse - boolean, True if we are checking a reverse select related
|
|
"""
|
|
if not field.rel:
|
|
return False
|
|
if field.rel.parent_link and not reverse:
|
|
return False
|
|
if restricted:
|
|
if reverse and field.related_query_name() not in requested:
|
|
return False
|
|
if not reverse and field.name not in requested:
|
|
return False
|
|
if not restricted and field.null:
|
|
return False
|
|
return True
|
|
|
|
# This function is needed because data descriptors must be defined on a class
|
|
# object, not an instance, to have any effect.
|
|
|
|
def deferred_class_factory(model, attrs):
|
|
"""
|
|
Returns a class object that is a copy of "model" with the specified "attrs"
|
|
being replaced with DeferredAttribute objects. The "pk_value" ties the
|
|
deferred attributes to a particular instance of the model.
|
|
"""
|
|
class Meta:
|
|
proxy = True
|
|
app_label = model._meta.app_label
|
|
|
|
# The app_cache wants a unique name for each model, otherwise the new class
|
|
# won't be created (we get an old one back). Therefore, we generate the
|
|
# name using the passed in attrs. It's OK to reuse an existing class
|
|
# object if the attrs are identical.
|
|
name = "%s_Deferred_%s" % (model.__name__, '_'.join(sorted(list(attrs))))
|
|
name = util.truncate_name(name, 80, 32)
|
|
|
|
overrides = dict([(attr, DeferredAttribute(attr, model))
|
|
for attr in attrs])
|
|
overrides["Meta"] = Meta
|
|
overrides["__module__"] = model.__module__
|
|
overrides["_deferred"] = True
|
|
return type(name, (model,), overrides)
|
|
|
|
# The above function is also used to unpickle model instances with deferred
|
|
# fields.
|
|
deferred_class_factory.__safe_for_unpickling__ = True
|