Add sample dags (#1)

Adds few sample DAGs showcasing various Airflow features

roll_d20::
* generates random number. Can read ENV var to override
* DAG structure

![image](https://github.com/user-attachments/assets/8d43cde6-4c89-453e-a626-b24798f2fb5f)

sample_ch_ddl::
* checks if table exists, if not — creates
* DAG structure

![image](https://github.com/user-attachments/assets/ba5e8251-8e87-4d36-afcc-16825e324856)

sample_ch_insert::
* has DAG params for number of randoms to insert
* updates dataset
* DAG structure 

![image](https://github.com/user-attachments/assets/71818527-988f-44d5-9319-1c6d06e49af5)

sample_ch_stats::
* triggered by dataset update from insert dag 
* DAG structure

![image](https://github.com/user-attachments/assets/fa0e9496-fa86-4dfe-95e8-325eb7bd3479)
* display stats task

![image](https://github.com/user-attachments/assets/fc38b389-87d1-4875-bde8-d9f8152cbca1)

Author: cra

README.md

@@ -1,2 +1,35 @@
 # sample-airflow-dags
-Example dags for DC Managed Airflow, showcasing interaction with other DC services
+Example dags for DobuleCloud Managed Airflow, showcasing interaction with other DC services
+
+Refer to documentation for Getting Started guide: https://double.cloud/docs/en/managed-airflow/get-started
+
+## ClickHouse connection
+
+You would need a ClickHouse connection named `ch_default` to make DAGs with tag `clickhouse` connect to your ClickHouse instance.
+If using DoubleCloud ClickHouse, create a generic connection with extra setting `{"secure": true}`. 
+
+## DAGs
+
+[roll_d20](./dags/roll_d20.py) is not connected to anything and can be used to check new setup. Once enabled, it runs on a cron schedule every 5 minutes. You can set env variable `RND_SEED_OVERRIDE` in DC Airflow cluster settings to specify custom random seed for reproducibility.
+
+![roll_d20_graph](./img/roll_d20_graph.png)
+
+---
+
+[sample_ch_ddl](./dags/sample_ch_ddl.py) checks if `sample_table` exists in clickhouse connection with connection_id `ch_default`.
+
+![sample_ch_ddl_graph](./img/sample_ch_ddl_graph.png)
+
+---
+
+[sample_ch_insert](./dags/sample_ch_insert.py) inserts specified number of rows in `sample_table` and updates dataset `clickhouse://sample_table`.
+
+![sample_ch_insert_graph](./img/sample_ch_insert_graph.png)
+
+---
+
+[sample_ch_stats](./dags/sample_ch_stats.py) computes stats on `sample_table` and outputs them in task logs. Triggered on updates in dataset `clickhouse://sample_table`
+
+![sample_ch_stats_graph](./img/sample_ch_stats_graph.png)
+
+![sample_ch_stats_log](./img/sample_ch_stats_log.png)

dags/roll_d20.py

@@ -0,0 +1,40 @@
+import os
+import random
+import pathlib
+from datetime import datetime as dt
+
+from airflow.decorators import dag, task
+
+
+@dag(
+    dag_id=pathlib.Path(__file__).stem,
+    description="Example DAG with two chained tasks that outputs a random number between 1 and 20",
+    schedule='*/5 * * * *',
+    start_date=dt(2024, 9, 1, 0, 0, 0),
+    catchup=False,
+    tags=["sample", "random"],
+)
+def roll_d20():
+    @task
+    def dice_roll():
+        seed = os.environ.get('RND_SEED_OVERRIDE')
+        if seed:
+            seed = int(seed)
+            print("Random seed override:", seed)
+            random.seed(seed)
+
+        return random.randint(1, 20)
+
+    @task
+    def roll_result(roll_value):
+        print("Hello from DoubleCloud")
+        print("You rolled", roll_value)
+
+    roll_result(roll_value=dice_roll())
+
+
+my_dag = roll_d20()
+
+
+if __name__ == '__main__':
+    my_dag.test()

dags/sample_ch_ddl.py

@@ -0,0 +1,66 @@
+import datetime
+import pathlib
+
+from airflow.utils.trigger_rule import TriggerRule
+from airflow.decorators import dag
+
+from airflow_clickhouse_plugin.operators.clickhouse import ClickHouseOperator
+from airflow.operators.empty import EmptyOperator
+from airflow.providers.common.sql.operators import sql
+from airflow_clickhouse_plugin.operators.clickhouse_dbapi import (
+    ClickHouseBaseDbApiOperator,
+)
+
+
+class ClickHouseBranchSQLOperator(
+    sql.BranchSQLOperator,
+    ClickHouseBaseDbApiOperator,
+):
+    """
+    temporary workaround for Airflow < 2.9.4
+    see https://github.com/bryzgaloff/airflow-clickhouse-plugin/issues/87
+    """
+
+    pass
+
+
+@dag(
+    dag_id=pathlib.Path(__file__).stem,
+    schedule=None,
+    start_date=datetime.datetime(2024, 9, 1, 0, 0, 0),
+    catchup=False,
+    dag_display_name="Create sample_table",
+    tags=["sample", "clickhouse", "ddl"],
+    max_active_runs=1,
+)
+def sample_ddl_stats():
+    check_tbl_exists = ClickHouseBranchSQLOperator(
+        task_id='check_if_sample_table_exists',
+        sql='EXISTS sample_table',
+        conn_id='ch_default',
+        follow_task_ids_if_true='do_nothing',
+        follow_task_ids_if_false='create_sample_table',
+    )
+
+    do_nothing = EmptyOperator(task_id="do_nothing")
+    create_tbl = ClickHouseOperator(
+        task_id='create_sample_table',
+        sql="""
+	    CREATE TABLE IF NOT EXISTS sample_table
+	    (
+            id UInt32,
+            value Float64,
+            category Enum8('A' = 1, 'B' = 2, 'C' = 3)
+        ) ENGINE = MergeTree() ORDER BY id;
+        """,
+        clickhouse_conn_id='ch_default',
+    )
+
+    check_tbl_exists >> [create_tbl, do_nothing]
+
+
+my_dag = sample_ddl_stats()
+
+
+if __name__ == '__main__':
+    my_dag.test()

dags/sample_ch_insert.py

@@ -0,0 +1,48 @@
+import datetime
+import pathlib
+
+from airflow.datasets import Dataset
+from airflow.decorators import dag, task
+from airflow.operators.empty import EmptyOperator
+from airflow.utils.trigger_rule import TriggerRule
+
+from airflow_clickhouse_plugin.operators.clickhouse import ClickHouseOperator
+
+
+sql_dir = pathlib.Path(__file__).absolute().parent / "sql"
+sample_table_dataset = Dataset('clickhouse://sample_table')
+
+
+@dag(
+    dag_id=pathlib.Path(__file__).stem,
+    schedule=None,
+    start_date=datetime.datetime(2024, 9, 1, 0, 0, 0),
+    catchup=False,
+    template_searchpath=[sql_dir],
+    dag_display_name="Insert data to sample_table",
+    tags=["sample", "clickhouse", "random"],
+    max_active_runs=1,
+    params={
+        'num_rows': 1_000_000,
+    },
+)
+def sample_ch_insert():
+    start = EmptyOperator(task_id="start")
+    insert_data = ClickHouseOperator(
+        task_id='insert_into_sample_table',
+        sql='insert_into_sample_table.sql',
+        clickhouse_conn_id='ch_default',
+        params={
+            "num_rows": "{{ params.num_rows }}",
+        },
+        outlets=[sample_table_dataset],
+    )
+
+    start >> insert_data
+
+
+my_dag = sample_ch_insert()
+
+
+if __name__ == '__main__':
+    my_dag.test()

dags/sample_ch_stats.py

@@ -0,0 +1,65 @@
+import datetime
+import pathlib
+
+from airflow.datasets import Dataset
+from airflow.decorators import dag, task
+from airflow.operators.empty import EmptyOperator
+from airflow.utils.trigger_rule import TriggerRule
+
+from airflow_clickhouse_plugin.operators.clickhouse import ClickHouseOperator
+
+
+sql_dir = pathlib.Path(__file__).absolute().parent / "sql"
+sample_table_dataset = Dataset('clickhouse://sample_table')
+
+
+@dag(
+    dag_id=pathlib.Path(__file__).stem,
+    schedule=sample_table_dataset,
+    start_date=datetime.datetime(2024, 9, 1, 0, 0, 0),
+    catchup=False,
+    template_searchpath=[sql_dir],
+    dag_display_name="Compute stats on sample_table",
+    tags=["sample", "clickhouse", "stats"],
+    max_active_runs=1,
+)
+def sample_ch_insert():
+    start = EmptyOperator(task_id="start")
+    compute_stats = ClickHouseOperator(
+        task_id='compute_stats_sample_table',
+        sql="""
+        SELECT 
+            category,
+            count() AS total_count,
+            avg(value) AS mean_value,
+            median(value) AS median_value,
+            stddevPop(value) AS std_dev,
+            min(value) AS min_value,
+            max(value) AS max_value
+        FROM sample_table
+        GROUP BY category
+        ORDER BY category;
+        """,
+        with_column_types=True,
+        clickhouse_conn_id='ch_default',
+    )
+
+    @task
+    def display_stats(upstream_xcom):
+        stats, names = upstream_xcom
+        print("Stats on sample_table:")
+        print(",".join(t for t, _ in names))
+        for row in stats:
+            print(row)
+
+    end = EmptyOperator(task_id="end")
+
+    start >> compute_stats
+    display_stats(compute_stats.output) >> end
+
+
+my_dag = sample_ch_insert()
+
+
+if __name__ == '__main__':
+    my_dag.test()

dags/sql/insert_into_sample_table.sql

@@ -0,0 +1,11 @@
+INSERT INTO sample_table (id, value, category)
+SELECT 
+    number AS id,
+    randNormal(50, 10) AS value,
+    multiIf(
+        rand() % 3 = 0, 'A',
+        rand() % 3 = 1, 'B',
+        'C'
+    ) AS category
+FROM numbers({{ params.num_rows }})
+SETTINGS max_insert_block_size = 100000;