Lets say I have the following simplified example:

from sqlalchemy.orm import DeclarativeBase, Mapped

class TableA(DeclarativeBase):
    col_name = Mapped[str | None]
    parent_id = Mapped[int]

class TableB(DeclarativeBase):
    col_name = Mapped[str | None]
    parent_id = Mapped[int]

class TableC(DeclarativeBase):
    col_name = Mapped[str | None]
    parent_id = Mapped[int]

MY_MAPPINGS = {
   "a__col_name" : func.coalesce(TableA.col_name, "").label("some_col_name"),
   "b__col_name" : func.coalesce(TableB.col_name, "").label("another__col_name"),
   "c__col_name" : func.coalesce(TableC.col_name, "").label("third__col_name"),
}

def get_query(mapping: str, parent_id: int):
    col = MY_MAPPINGS[mapping]
    return select(col)

That should be fine. But now what if I want to add a filter on this query for parent_id, how would I do this? Ideally I would want to do something like

.filter(col.table.parent_id = parent_id)

But col is type sqlalchemy.sql.elements.Label and col.table is None. What do I do here?