Django源码分析-ORM框架解读
在Django的ORM中,QuerySet
是一个非常重要的组成部分,它封装了数据库的查询和返回结果。以下是QuerySet
部分源代码的简化版本:
class QuerySet:
def __init__(self, model=None):
self.model = model
self._database = None
self._query = None
def __iter__(self):
if self._result_cache is None:
self._result_cache = list(self._iterable_class(self))
return iter(self._result_cache)
def __getitem__(self, k):
if isinstance(k, slice):
query = self._clone()
if k.start is not None:
start = k.start
else:
start = 0
if start < 0:
start += len(self)
if k.stop is not None:
stop = k.stop
else:
stop = len(self)
if stop < 0:
stop += len(self)
if start > stop:
return new_queryset = self._no_results()
return queryset[start:stop]
elif isinstance(k, int):
if k < 0:
k += len(self)
return list(self)[k]
raise TypeError
def _clone(self):
klass = self.__class__
query = self._query
new = klass(model=self.model, query=query.clone())
new._db = self._db
new._hints = self._hints
new._values_select = self._values_select
new._defered_fields = self._defered_fields
new._only_fields = self._only_fields
new._prefetch_related_lookups = self._prefetch_related_lookups
return new
def all(self):
if self._query is None:
return self._no_filters()
return self._clone()
def filter(self, *args, **kwargs):
clone = self._clone()
clone._query.add_q(Q(*args, **kwargs))
return clone
def exclude(self, *args, **kwargs):
clone = self._clone()
clone._query.add_q(~Q(*args, **kwargs))
return clone
def _no_filters(self):
clone = self._clone()
clone._query = None
return clone
这个简化版本的QuerySet
类展示了如何初始化一个查询集合,如何使用切片和索引进行查询,以及如何添加过滤器(filter
和exclude
方法)。这里的QuerySet
类只是一个示例,并不完整,因为实际的Django ORM中的QuerySet
类包含了大量的其他功能和复杂逻辑。
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