Putting it all together

Introduction to Data Engineering

Vincent Vankrunkelsven

Data Engineer @ DataCamp

The ETL function

def extract_table_to_df(tablename, db_engine):
  return pd.read_sql("SELECT * FROM {}".format(tablename), db_engine)

def split_columns_transform(df, column, pat, suffixes): # Converts column into str and splits it on pat...
def load_df_into_dwh(film_df, tablename, schema, db_engine): return pd.to_sql(tablename, db_engine, schema=schema, if_exists="replace")
db_engines = { ... } # Needs to be configured def etl(): # Extract film_df = extract_table_to_df("film", db_engines["store"]) # Transform film_df = split_columns_transform(film_df, "rental_rate", ".", ["_dollar", "_cents"]) # Load load_df_into_dwh(film_df, "film", "store", db_engines["dwh"])
Introduction to Data Engineering

Airflow refresher

Airflow logo

 

  • Workflow scheduler
  • Python
  • DAGs

Conceptual example of a DAG

  • Tasks defined in operators (e.g. BashOperator)
Introduction to Data Engineering

Scheduling with DAGs in Airflow

from airflow.models import DAG

dag = DAG(dag_id="sample",
          ...,
          schedule_interval="0 0 * * *")

# cron
# .------------------------- minute           (0 - 59)
# | .----------------------- hour             (0 - 23)
# | | .--------------------- day of the month (1 - 31)
# | | | .------------------- month            (1 - 12)
# | | | | .----------------- day of the week  (0 - 6)
# * * * * * <command>

# Example
0 * * * * # Every hour at the 0th minute

cf. https://crontab.guru

Introduction to Data Engineering

The DAG definition file

from airflow.models import DAG
from airflow.operators.python_operator import PythonOperator

dag = DAG(dag_id="etl_pipeline",
          schedule_interval="0 0 * * *")

etl_task = PythonOperator(task_id="etl_task", python_callable=etl, dag=dag)
etl_task.set_upstream(wait_for_this_task)
Introduction to Data Engineering

The DAG definition file

from airflow.models import DAG
from airflow.operators.python_operator import PythonOperator

...

etl_task.set_upstream(wait_for_this_task)

Saved as etl_dag.py in ~/airflow/dags/

Introduction to Data Engineering

Airflow UI

Screenshot of Airflow UI

Introduction to Data Engineering

Let's practice!

Introduction to Data Engineering

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