Add 'purify'
parent
484f9d357e
commit
62bd91b8ff
242
purify.md
Normal file
242
purify.md
Normal file
@ -0,0 +1,242 @@
|
||||
```python
|
||||
from django.db.models import QuerySet
|
||||
from django.db.models.expressions import BaseExpression, Combinable
|
||||
from django.db.models.query import ValuesIterable
|
||||
from django.db.models.manager import Manager
|
||||
|
||||
"""
|
||||
|
||||
Base Idea:
|
||||
- to have a queryset function that easily allows you to build some sort of "pure class" in a queryset.
|
||||
- make it able to seamlessly use annotation functions
|
||||
- allow callback modication of data, which is needed if your dataclass is frozen.
|
||||
|
||||
By default the PureManager and PureQuerySet will use PureDataclass as handler, expecting your pureclass to be a dataclasses.dataclass type.
|
||||
|
||||
An Example:
|
||||
@dataclass
|
||||
class MyClass
|
||||
id: int
|
||||
some_relation: str
|
||||
next_id: int
|
||||
|
||||
SomeModel.objects.filter(...).exclude(...).purify(MyClass, some_relation=F('some__model__relation'), next_id=Lambda(lambda x: x.get('id')+1))
|
||||
|
||||
This allows you to move an iterator into another layer, where it either can be consumed, or used as an input for another queryset call,
|
||||
but still guaranteeing, that regular usage of the iterator will not yield any smart object.
|
||||
It is good if you want to build a best-of-both-worlds approach for subquery-capable repository pattern, which is one of the biggest issues if you want
|
||||
to keep your business logic out of the repo layer, but still want to utilize djangos queryset mechanics properly.
|
||||
|
||||
"""
|
||||
|
||||
## Useful for queryset function purify()
|
||||
class BaseLeap:
|
||||
skip = False # if skip is true, this leap will not be actually processed.
|
||||
resolves_field = True # if resolves_field is true, this leap will be called for a single field with resolve()
|
||||
post_processing = False # if post_processing is true, this leap will in the end be called with dbdata, and be able to manipulate the whole dictionary.
|
||||
|
||||
def resolve(self, model, dbdata):
|
||||
raise NotImplementedError
|
||||
|
||||
def post_process(self, model, dbdata):
|
||||
raise NotImplementedError
|
||||
|
||||
class Leap(BaseLeap):
|
||||
""" value function that leaps SQL handling. """
|
||||
def __init__(self, value=None):
|
||||
self.value = value
|
||||
|
||||
def resolve(self, model, dbdata):
|
||||
return self.value
|
||||
|
||||
class Lambda(Leap):
|
||||
""" leap value that calls a lambda expression. """
|
||||
def __init__(self, callback):
|
||||
self.callback = callback if callable(callback) else None
|
||||
|
||||
def resolve(self, model, dbdata):
|
||||
# at this point i could check if callback needs 0-2 arguments and decide the call.
|
||||
if self.callback:
|
||||
return self.callback(dbdata)
|
||||
|
||||
class Skip(BaseLeap):
|
||||
""" Skips this key from being retrieved from the database or used in the dataclass instantiation """
|
||||
skip = True
|
||||
resolves_field = False
|
||||
|
||||
class Callback(BaseLeap):
|
||||
resolves_field = False
|
||||
post_processing = True
|
||||
def __init__(self, callback):
|
||||
self.callback = callback
|
||||
def post_process(self, model, dbdata):
|
||||
if self.callback:
|
||||
return self.callback(dbdata)
|
||||
|
||||
## Wrapper to handle some sort of pure baseclass
|
||||
class PureHandler:
|
||||
""" handler for a pure baseclass
|
||||
|
||||
defines how a pureclass can be created, and how to retrieve all field names, and the required ones.
|
||||
"""
|
||||
|
||||
@classmethod
|
||||
def wrap(cls, klass):
|
||||
return cls(klass)
|
||||
|
||||
def __init__(self, klass):
|
||||
self.klass = klass
|
||||
|
||||
def create(self, **kwargs):
|
||||
return self.klass(**kwargs)
|
||||
|
||||
def get_field_names(self):
|
||||
return self.klass.__dict__.keys()
|
||||
|
||||
@property
|
||||
def pureclass(self):
|
||||
return self.klass
|
||||
|
||||
@property
|
||||
def required_keys(self):
|
||||
return self.get_field_names()
|
||||
|
||||
|
||||
class PureDict(PureHandler):
|
||||
""" PureHandler that outputs a dictionary """
|
||||
|
||||
def __init__(self, klass=None):
|
||||
# it is not required to define dict, but you could do OrderedDict e.g.
|
||||
self.klass = klass or dict
|
||||
|
||||
def get_field_names(self):
|
||||
# dictionary has no required fields.
|
||||
return []
|
||||
|
||||
|
||||
class PureDataclass(PureHandler):
|
||||
""" handles dataclasses.dataclass derivatives """
|
||||
|
||||
def create(self, **kwargs):
|
||||
# clean field names to be only valid if they are on the dataclass.
|
||||
pure_fields = self.get_field_names()
|
||||
kwargs = {k: v for k, v in kwargs.items() if k in pure_fields}
|
||||
return self.klass(**kwargs)
|
||||
|
||||
def get_field_names(self):
|
||||
return list(self.klass.__dataclass_fields__.keys())
|
||||
|
||||
# @TODO: PurePydantic
|
||||
|
||||
###### QuerySet Plugin.
|
||||
|
||||
class PureIterable(ValuesIterable):
|
||||
"""
|
||||
Iterable returned by purify() that yields a pure class for each row.
|
||||
Replaces the standard iterable of the queryset.
|
||||
"""
|
||||
|
||||
def __iter__(self):
|
||||
queryset = self.queryset
|
||||
model = self.queryset.model
|
||||
query = queryset.query
|
||||
compiler = query.get_compiler(queryset.db)
|
||||
pure_data = getattr(queryset, '_pureclass_extra', {})
|
||||
pure_handler = queryset._pureclass
|
||||
|
||||
# extra(select=...) cols are always at the start of the row.
|
||||
names = [
|
||||
*query.extra_select,
|
||||
*query.values_select,
|
||||
*query.annotation_select,
|
||||
]
|
||||
indexes = range(len(names))
|
||||
|
||||
for row in compiler.results_iter(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size):
|
||||
dbdata = {names[i]: row[i] for i in indexes}
|
||||
# post-processors will be able to rewrite the whole dictionary.
|
||||
post_processors = []
|
||||
# we overwrite db data bluntly for now. actually we would provide callbacks the current dict.
|
||||
for k, v in pure_data.items():
|
||||
if v.resolves_field:
|
||||
dbdata[k] = v.resolve(model, dbdata)
|
||||
if v.post_processing:
|
||||
post_processors.append(v)
|
||||
if post_processors:
|
||||
for processor in post_processors:
|
||||
processed = processor.post_process(model, dbdata)
|
||||
if processed is not None:
|
||||
dbdata = processed
|
||||
yield pure_handler.create(**dbdata)
|
||||
|
||||
|
||||
class PureQuerySetMixin:
|
||||
_pureclass_handler = PureDataclass
|
||||
|
||||
def purify(self, *args, **kwargs):
|
||||
"""
|
||||
generates pure objects
|
||||
|
||||
Acts like values(), however:
|
||||
- first argument is a pureclass or purehandler, if not a string.
|
||||
- if pureclass is not defined in purify, you have to define it on the queryset, or the model, with _pureclass,
|
||||
otherwise it will raise a RuntimeError.
|
||||
- keyword arguments of type "Leap" are used as deferred values, and resolved independently.
|
||||
- values() is called with every required_key on the dataclass not handled by a Leap
|
||||
"""
|
||||
if len(args) and not isinstance(args[0], str):
|
||||
# we assume this is our dataclass
|
||||
# @TODO better checks.
|
||||
handler = args[0]
|
||||
args = args[1:]
|
||||
else:
|
||||
# determine dataclass.
|
||||
handler = getattr(self, '_pureclass', getattr(self.model, '_pureclass', None))
|
||||
if not handler:
|
||||
raise RuntimeError("Trying to purify a class without destination class.")
|
||||
|
||||
if not isinstance(handler, PureHandler):
|
||||
handler = self._pureclass_handler.wrap(handler)
|
||||
|
||||
all_keys = [*args, *kwargs.keys()]
|
||||
unhandled_keys = list(set(handler.required_keys) - set(all_keys))
|
||||
args = [*args, *unhandled_keys]
|
||||
|
||||
new_kw = {}
|
||||
extra = {}
|
||||
for k, v in kwargs.items():
|
||||
if isinstance(v, Leap):
|
||||
if not v.skip:
|
||||
extra[k] = v
|
||||
elif isinstance(v, BaseExpression) or isinstance(v, Combinable):
|
||||
new_kw[k] = v
|
||||
else:
|
||||
new_kw[k] = v
|
||||
|
||||
# copy ourself with values() and save the results on the cloned queryset.
|
||||
values = self.values(*args, **new_kw)
|
||||
values._iterable_class = PureIterable
|
||||
values._pureclass_extra = extra
|
||||
values._pureclass = handler
|
||||
return values
|
||||
|
||||
|
||||
class PureQuerySet(PureQuerySetMixin, QuerySet):
|
||||
# overwrite cloning.
|
||||
def _clone(self):
|
||||
c = super()._clone()
|
||||
for key in ['_pureclass', '_pureclass_extra', '_pureclass_handler']:
|
||||
if hasattr(self, key):
|
||||
setattr(c, key, getattr(self, key))
|
||||
return c
|
||||
|
||||
# i use a mixin instead for better clarity. purify is completely safe, as it does not call _chain.
|
||||
# however you can also simply do:
|
||||
#class PureManager(BaseManager.from_queryset(PureQuerySet)):
|
||||
# pass
|
||||
|
||||
|
||||
class PureManager(PureQuerySetMixin, Manager):
|
||||
def get_queryset(self):
|
||||
return PureQuerySet(self.model, using=self._db)
|
||||
```
|
||||
Loading…
Reference in New Issue
Block a user