code: def get_dag(
      *,
      dag_id: str,
      fields: Collection[str] | None = None,
      session: Session = NEW_SESSION,
  ) -> APIResponse:
      """Get basic information about a DAG."""
      dag = session.scalar(
          select(DagModel).where(DagModel.dag_id == dag_id)
      )
      if dag is None:
          raise NotFound(
              "DAG not found",
              detail=f"The DAG with dag_id: {dag_id} was not found",
          )
      try:
          dag_schema = DAGSchema(only=fields) if fields else DAGSchema()
      except ValueError as e:
          raise BadRequest("DAGSchema init error", detail=str(e))
      return dag_schema.dump(
          dag,
      )
  
imports: from __future__ import annotations
  from http import HTTPStatus
  from typing import TYPE_CHECKING, Collection
  from connexion import NoContent
  from flask import g, request
  from marshmallow import ValidationError
  from sqlalchemy import select, update
  from sqlalchemy.sql.expression import or_
  from airflow.api_connexion import security
  from airflow.api_connexion.exceptions import AlreadyExists, BadRequest, NotFound
  from airflow.api_connexion.parameters import apply_sorting, check_limit, format_parameters
  from airflow.api_connexion.schemas.dag_schema import DAGCollection, DAGCollectionSchema, DAGDetailSchema, DAGSchema, dag_schema, dags_collection_schema
  from airflow.exceptions import AirflowException, DagNotFound
  from airflow.models.dag import DagModel, DagTag
  from airflow.utils.airflow_flask_app import get_airflow_app
  from airflow.utils.db import get_query_count
  from airflow.utils.session import NEW_SESSION, provide_session
  from airflow.www.extensions.init_auth_manager import get_auth_manager
label_desc: Use image node_id 1 for calling a global function with example usage: get_dag() and returns: dag_schema