Async support for magic parameters

[simonw]

I want to run a magic parameter thing that does something async.

[simonw]

Relevant code:

datasette/datasette/views/database.py

Lines 794 to 818 in b0b600b

	class MagicParameters(dict):
	def __init__(self, data, request, datasette):
	super().__init__(data)
	self._request = request
	self._magics = dict(
	itertools.chain.from_iterable(
	pm.hook.register_magic_parameters(datasette=datasette)
	)
	)
	def __len__(self):
	# Workaround for 'Incorrect number of bindings' error
	# https://github.com/simonw/datasette/issues/967#issuecomment-692951144
	return super().__len__() or 1
	def __getitem__(self, key):
	if key.startswith("_") and key.count("_") >= 2:
	prefix, suffix = key[1:].split("_", 1)
	if prefix in self._magics:
	try:
	return self._magics[prefix](suffix, self._request)
	except KeyError:
	return super().__getitem__(key)
	else:
	return super().__getitem__(key)

datasette/datasette/views/database.py

Line 394 in b0b600b

params_for_query = MagicParameters(params, request, datasette)

datasette/datasette/views/database.py

Line 526 in b0b600b

params_for_query = MagicParameters(params, request, datasette)

Instead of dynamic dictionary lookups for everything I'll need to first extract the :params using this:

datasette/datasette/utils/__init__.py

Lines 1141 to 1153 in b0b600b

	@documented
	def named_parameters(sql: str) -> List[str]:
	"""
	Given a SQL statement, return a list of named parameters that are used in the statement
	e.g. for ``select * from foo where id=:id`` this would return ``["id"]``
	"""
	sql = _single_line_comment_re.sub("", sql)
	sql = _multi_line_comment_re.sub("", sql)
	sql = _single_quote_re.sub("", sql)
	sql = _double_quote_re.sub("", sql)
	# Extract parameters from what is left
	return _named_param_re.findall(sql)

Then resolve them prior to executing the query.