In #156 @phi-friday wanted to pass sa_column_kwargs={"type_": Unicode} to a Field to set the column to nvarchar, doing this causes an exception:

File "/usr/local/lib/python3.9/site-packages/sqlalchemy/sql/schema.py", line 1586, in __init__
raise exc.ArgumentError(
sqlalchemy.exc.ArgumentError: May not pass type_ positionally and as a keyword.

sa_type is passed by get_column_from_field as a positional argument, so passing it through at a kwarg leads to this exception.

PR checks if type_ is in the kwargs, and if it is it pops it from the kwargs and sets sa_type to its value.

Also added a test for this case, @tiangolo is issue-related tests in a separate directory a thing you like? It's not done in FastAPI or here, so if not I'll move it.

Edit: whoops, forgot the sa_column argument existed, given that this seems kind of pointless 🤔