Airflow sql_path not able to read the sql files when passed as Jinja Template Variable - airflow

Question

I am trying to use Jinja template variable as against using Variable.get('sql_path'), So as to avoid hitting DB for every scan of the dag file
Original code
import datetime
import os
from functools import partial
from datetime import timedelta
from airflow.models import DAG,Variable
from airflow.contrib.operators.snowflake_operator import SnowflakeOperator
from alerts.email_operator import dag_failure_email
SNOWFLAKE_CONN_ID = 'etl_conn'
tmpl_search_path = []
for subdir in ['business/', 'audit/', 'business/transform/']:
tmpl_search_path.append(os.path.join(Variable.get('sql_path'), subdir))
def get_db_dag(
*,
dag_id,
start_date,
schedule_interval,
max_taskrun,
max_dagrun,
proc_nm,
load_sql
):
default_args = {
'owner': 'airflow',
'start_date': start_date,
'provide_context': True,
'execution_timeout': timedelta(minutes=max_taskrun),
'retries': 0,
'retry_delay': timedelta(minutes=3),
'retry_exponential_backoff': True,
'email_on_retry': False,
}
dag = DAG(
dag_id=dag_id,
schedule_interval=schedule_interval,
dagrun_timeout=timedelta(hours=max_dagrun),
template_searchpath=tmpl_search_path,
default_args=default_args,
max_active_runs=1,
catchup='{{var.value.dag_catchup}}',
on_failure_callback=alert_email_callback,
)
load_table = SnowflakeOperator(
task_id='load_table',
sql=load_sql,
snowflake_conn_id=SNOWFLAKE_CONN_ID,
autocommit=True,
dag=dag,
)
load_vcc_svc_recon
return dag
# ======== DAG DEFINITIONS #
edw_table_A = get_db_dag(
dag_id='edw_table_A',
start_date=datetime.datetime(2020, 5, 21),
schedule_interval='0 5 * * *',
max_taskrun=3, # Minutes
max_dagrun=1, # Hours
load_sql='recon/extract.sql',
)
When I have replaced Variable.get('sql_path') with Jinja Template '{{var.value.sql_path}}' as below and ran the Dag, it threw an error as below, it was not able to get the file from the subdirectory of the SQL folder
tmpl_search_path = []
for subdir in ['bus/', 'audit/', 'business/snflk/']:
tmpl_search_path.append(os.path.join('{{var.value.sql_path}}', subdir))
Got below error as
inja2.exceptions.TemplateNotFound: extract.sql

Answer 1

Templates are not rendered everywhere in a DAG script. Usually they are rendered in the templated parameters of Operators. So, unless you pass the elements of tmpl_search_path to some templated parameter {{var.value.sql_path}} will not be rendered.
The template_searchpath of DAG is not templated. That is why you cannot pass Jinja templates to it.
The options of which I can think are
Hardcode the value of Variable.get('sql_path') in the pipeline script.
Save the value of Variable.get('sql_path') in a configuration file and read it from there in the pipeline script.
Move the Variable.get() call out of the for-loop. This will result in three times fewer requests to the database.
More info about templating in Airflow.