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Error when using "alias" as a field name in m2m tables

See original GitHub issue

Well, it’s me again. 😃 I met something really weird. It seems like we can’t use field name alias in m2m tables i.e. prefetch_related won’t work with it.

Is it reserved for something?

I have a model structure like this:

class ModelOne(Model):
    id = fields.IntField(pk=True)
    name = fields.TextField()
    many_to_many = fields.ManyToManyField('models.ModelTwo')

class ModelTwo(Model):
    id = fields.IntField(pk=True)
    name = fields.TextField()
    alias = fields.TextField()

And after using prefetch related (code snippet below):

async for item in ModelOne.all().prefetch_related('many_to_many'):
    print(item)

we got errors like these:

Traceback (most recent call last):
  File "/opt/project/src/server.py", line 54, in <module>
    asyncio.run(main())
  File "/usr/local/lib/python3.7/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "/usr/local/lib/python3.7/asyncio/base_events.py", line 579, in run_until_complete
    return future.result()
  File "/opt/project/src/server.py", line 47, in main
    async for item in ModelOne.all().prefetch_related('many_to_many'):
  File "/usr/local/lib/python3.7/site-packages/tortoise/queryset.py", line 512, in __aiter__
    for val in await self:
  File "/usr/local/lib/python3.7/site-packages/tortoise/queryset.py", line 521, in _execute
    ).execute_select(self.query, custom_fields=list(self._annotations.keys()))
  File "/usr/local/lib/python3.7/site-packages/tortoise/backends/base/executor.py", line 90, in execute_select
    await self._execute_prefetch_queries(instance_list)
  File "/usr/local/lib/python3.7/site-packages/tortoise/backends/base/executor.py", line 327, in _execute_prefetch_queries
    await self._do_prefetch(instance_list, field, related_query)
  File "/usr/local/lib/python3.7/site-packages/tortoise/backends/base/executor.py", line 320, in _do_prefetch
    return await self._prefetch_m2m_relation(instance_id_list, field, related_query)
  File "/usr/local/lib/python3.7/site-packages/tortoise/backends/base/executor.py", line 232, in _prefetch_m2m_relation
    *[getattr(related_query_table, field).as_(field) for field in related_query.fields],
  File "/usr/local/lib/python3.7/site-packages/tortoise/backends/base/executor.py", line 232, in <listcomp>
    *[getattr(related_query_table, field).as_(field) for field in related_query.fields],
AttributeError: 'NoneType' object has no attribute 'as_'

tortoise-orm==0.14.0, asyncpg==0.19.0

PS: If you rename alias->alias2 this code will work.