Check for ID field index before querying tables via id

[acannistra]

This function is very, very slow on large tables without an index onosm_id. We should at the very least warn if an index doesn't exist here. This might mean we have a startup function that looks for all of the required indices (this one, and some geometry indices needed elsewhere).

changegen/changegen/db.py

Lines 76 to 83 in ba1ed0f

	def get_feature_by_id(self, layer, id, id_field):
	_q = f"SELECT * from {layer} WHERE {layer}.{id_field} = {id}"
	_r = self.data.ExecuteSQL(_q)
	if len(_r) > 1:
	warnings.warn(
	f"More than one ID match for {id_field}:{id} (layer: {layer})"
	)
	return _r.GetNextFeature()

We could also add the index, but that's harder..