How to invoke Python function in TriggerDagRunOperator

Question

In am trying to call DAG from another DAG( target_dag from parent_dag).

My parent_dag code is :

from datetime import datetime
from airflow.models import DAG
from airflow.operators.python_operator import PythonOperator
from airflow.models import Variable
from airflow.operators.trigger_dagrun import TriggerDagRunOperator

def read_metadata(**kwargs):
    asqldb_kv = Variable.get("asql_kv")
    perfom some operations based on asqldb_kv and populate the result_dictionary list
    if len(result_dictionary) > 0:
       my_var = Variable.set("num_runs", len(result_dictionary))
       ti = kwargs['ti']
       ti.xcom_push(key='res', value=result_dictionary)

            
default_args = {
    'start_date': datetime(year=2021, month=6, day=19),
    'provide_context': True
}

with DAG(
    dag_id='parent_dag',
    default_args=default_args,
    schedule_interval='@once',
    description='Test Trigger DAG'
) as dag:

    trigger = TriggerDagRunOperator(

        task_id="test_trigger_dagrun",
        python_callable=read_metadata,
        trigger_dag_id="target_dag"
    )

I am getting the below error :

airflow.exceptions.AirflowException: Invalid arguments were passed to TriggerDagRunOperator (task_id: test_trigger_dagrun). Invalid arguments were:
**kwargs: {'python_callable': <function read_metadata at 0x7ff5f4159620>}

Any help appreciated.

Edit :

python_callable is depreciated in TriggerDagRunOperator - Airflow 2.0.

My requirement is :

I need to access Azure Synapse and get a variable (Say 3). Based on retrieved variable, I need to create tasks dynamically. Say, if Synapse has 3 , then I need to create 3 tasks.

My idea was :

DAG 1 - Access Azure synapse and get Variable. Update this to Airflow Variable. Trigger DAG2 using TriggerDagRunOperator.

DAG 2 - Create tasks depending on the Airflow Variable updated in DAG 1.

Any inputs how can I achieve this?