我试图获取两个QuerySet之间的区别，对我来说，重要的是，这个区别的答案应该是QuerySet。因此，自然的解决方案是使用Django queryset的差分方法。但是，当我尝试这样做时，我收到以下错误：
NotSupportedError: difference is not supported on this database backend.
这是我想做的事情：
In [4]: type(small_qs)
Out[4]: django.db.models.query.QuerySet
In [5]: type(bigger_qs)
Out[5]: django.db.models.query.QuerySet
In [6]: bigger_qs.difference(small_qs)
重要提示：两个查询集来自同一模型。
其他有用的信息：
这是完整的输出：
Out[6]: ----------------------------------------------------------------
NotSupportedError Traceback (most recent call
last)
/usr/local/lib/python3.6/site-packages/IPython/core/formatters.py in
__call__(self, obj)
700 type_pprinters=self.type_printers,
701 deferred_pprinters=self.deferred_printers)
702 printer.pretty(obj)
703 printer.flush()
704 return stream.getvalue()
/usr/local/lib/python3.6/site-packages/IPython/lib/pretty.py in
pretty(self, obj)
398 if cls is not object \
399 and
callable(cls.__dict__.get('__repr__')):
400 return _repr_pprint(obj, self, cycle)
401
402 return _default_pprint(obj, self, cycle)
/usr/local/lib/python3.6/site-packages/IPython/lib/pretty.py in
_repr_pprint(obj, p, cycle)
693 """A pprint that just redirects to the normal repr function."""
694 # Find newlines and replace them with p.break_()
695 output = repr(obj)
696 for idx,output_line in enumerate(output.splitlines()):
697 if idx:
/usr/local/lib/python3.6/site-packages/django/db/models/query.py in
__repr__(self)
246
247 def __repr__(self):
248 data = list(self[:REPR_OUTPUT_SIZE + 1])
249 if len(data) > REPR_OUTPUT_SIZE:
250 data[-1] = "...(remaining elements truncated)..."
/usr/local/lib/python3.6/site-packages/django/db/models/query.py in
__iter__(self)
270 - Responsible for turning the rows into model
objects.
271 """
272 self._fetch_all()
273 return iter(self._result_cache)
274
/usr/local/lib/python3.6/site-packages/django/db/models/query.py in
_fetch_all(self)
1177 def _fetch_all(self):
1178 if self._result_cache is None:
1179 self._result_cache = list(self._iterable_class(self))
1180 if self._prefetch_related_lookups and not
self._prefetch_done:
1181 self._prefetch_related_objects()
/usr/local/lib/python3.6/site-packages/django/db/models/query.py in
__iter__(self)
51 # Execute the query. This will also fill compiler.select,
klass_info,
52 # and annotations.
53 results =
compiler.execute_sql(chunked_fetch=self.chunked_fetch,
chunk_size=self.chunk_size)
54 select, klass_info, annotation_col_map = (compiler.select,
compiler.klass_info,
55
compiler.annotation_col_map)
/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py
in execute_sql(self, result_type, chunked_fetch, chunk_size)
1053 result_type = NO_RESULTS
1054 try:
1055 sql, params = self.as_sql()
1056 if not sql:
1057 raise EmptyResultSet
/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py
in as_sql(self, with_limits, with_col_aliases)
452 if combinator:
453 if not getattr(features,
'supports_select_{}'.format(combinator)):
454 raise NotSupportedError('{} is not supported
on this database backend.'.format(combinator))
455 result, params = self.get_combinator_sql(combinator,
self.query.combinator_all)
456 else:
NotSupportedError: difference is not supported on this database backend.
请，如果需要更多数据，请告诉我。
答案 0 :(得分：1)
根据this ticket，django并未正式支持MariaDB。大多数功能显然都存在，但是确定版本或区分MySQL和MariaDB似乎有些困难。我猜测您看到的错误与此有关。
也就是说，根据您要执行的操作，difference可能实际上并不是解决问题的“自然方法”。如果（我怀疑）您的两个查询集实际上在同一模型上，则执行所需操作的最简单方法是使用exclude。遵循以下原则：
bigger_qs.exclude(id__in=smaller_qs)
这不会产生相同的SQL（difference使用EXCEPT，而exclude使用WHERE NOT），则应该产生相同的SQL集。结果（可能顺序不同）。
答案 1 :(得分：0)
此代码可能会帮助您
check = Qs1.objects.all()
prg=[]
[prg.append(x.ref) for x in check]
difference = (Qs2.objects.exclude(ref__in=prg).values())