Source code for fsh_lib.transformers

"""Body→kwargs transformer helpers shared by generated builders.

Generated update builders one-line through :func:`build_patch_kwargs`
to read ``body.model_fields_set`` and emit a column-kwargs dict the
SQL ``update(...).values(**...)`` consumes.  The same one-shot
extraction would otherwise be repeated per resource as a chain of
``if "<field>" in body.model_fields_set: out["<field>"] = ...`` lines
in every transformer module.
"""

from __future__ import annotations

from typing import TYPE_CHECKING, Any

if TYPE_CHECKING:
    from collections.abc import Iterable

    from pydantic import BaseModel




def build_patch_kwargs(
    body: BaseModel,
    fields: Iterable[str],
) -> dict[str, Any]:
    """Project the explicitly-set subset of *fields* off *body* into a dict.

    PATCH semantics: a field that the client *did not* send must
    not appear in the returned dict, so the SQL ``UPDATE`` only
    touches columns the client meant to change.  ``body.model_fields_set``
    is pydantic's record of which attributes were populated from
    input (vs. left at their default), so iterating it is the
    correct gate -- a ``None`` *value* the client explicitly sent
    still passes through.

    Args:
        body: The parsed pydantic request model.
        fields: Field names the caller wants to consider.  Names
            absent from *body*'s declared fields are ignored.

    Returns:
        A ``dict`` mapping each set field to its value on *body*.
        The caller typically annotates the receiving variable with
        the per-resource ``{Resource}UpdateKwargs`` ``TypedDict``
        (``total=False``) so type-checkers see the result as the
        expected partial shape.

    """
    set_fields = body.model_fields_set
    return {name: getattr(body, name) for name in fields if name in set_fields}



__all__ = ["build_patch_kwargs"]