Apache airflow with conditional statements - bash

Question

I am new to Airflow. I want to do an operation like below using airflow operators.
Briefly I want to read some data from a database table and according to the values of a column in that table I want to do different tasks.
This is the table which I used to get data.
+-----------+--------+
| task_name | status |
+-----------+--------+
| a | 1 |
| b | 2 |
| c | 4 |
| d | 3 |
| e | 4 |
+-----------+--------+
From the above table I want to select the rows where status=4 and according to their task name run the relevant jar file (for running jar files I am planning to use Bash Operator). I want to execute this task using Airflow. Note that I am using PostgreSQL.
This is the code which I have implemented so far.
from airflow.models import DAG
from airflow.operators.postgres_operator import PostgresOperator
from datetime import datetime, timedelta
from airflow import settings
#set the default attributes
default_args = {
'owner': 'Airflow',
'start_date': datetime(2020,10,4)
}
status_four_dag = DAG(
dag_id = 'status_check',
default_args = default_args,
schedule_interval = timedelta(seconds=5)
)
test=PostgresOperator(
task_id='check_status',
sql='''select * from table1 where status=4;''',
postgres_conn_id='test',
database='status',
dag=status_four_dag,
)
I am stuck in the place where I want to check the task_name and call the relevant BashOperators.
Your support is appreciated. Thank you.

Answer 1

XComs are used for communicating messages between tasks. Send the JAR filename and other arguments for forming the command to xcom and consume it in the subsequent tasks.
For example,
check_status >> handle_status
check_status - checks status from DB and write JAR filename and arguments to xcom
handle_status - pulls the JAR filename and arguments from xcom, forms the command and execute it
Sample code:
def check_status(**kwargs):
if randint(1, 100) % 2 == 0:
kwargs["ti"].xcom_push("jar_filename", "even.jar")
else:
kwargs["ti"].xcom_push("jar_filename", "odd.jar")
with DAG(dag_id='new_example', default_args=default_args) as dag:
t0 = PythonOperator(
task_id="check_status",
provide_context=True,
python_callable=check_status
)
t1 = BashOperator(
task_id="handle_status",
bash_command="""
jar_filename={{ ti.xcom_pull(task_ids='check_status', key='jar_filename') }}
echo "java -jar ${jar_filename}"
"""
)
t0 >> t1