Python 气流-如何在for循环的迭代之间设置任务依赖关系?
我使用气流在for循环内部运行一组任务。循环的目的是遍历数据库表名列表并执行以下操作:Python 气流-如何在for循环的迭代之间设置任务依赖关系?,python,etl,airflow,Python,Etl,Airflow,我使用气流在for循环内部运行一组任务。循环的目的是遍历数据库表名列表并执行以下操作: for table_name in list_of_tables: if table exists in database (BranchPythonOperator) do nothing (DummyOperator) else: create table (JdbcOperator) insert records into table (JdbcO
for table_name in list_of_tables:
if table exists in database (BranchPythonOperator)
do nothing (DummyOperator)
else:
create table (JdbcOperator)
insert records into table (JdbcOperator, Trigger on One Success)
在Web UI上,显示如下所示:
当前,Airflow从上到下再从左到右执行此图像中的任务,如:tbl\u exists\u fake\u table\u one
-->tbl\u exists\u fake\u table\u two
-->tbl\u create\u fake\u table\u one
,等等
但是,fake\u table\u two
的insert
语句取决于正在更新的fake\u table\u one
,该依赖关系当前未被捕获。(从技术上讲,这种依赖性是通过表名列表的顺序捕获的,但我相信在更复杂的情况下,这很容易出错)
我希望运行与fake\u table\u one
相关的所有任务,然后运行与fake\u table\u two
相关的所有任务。我如何在气流中实现这一点
完整代码如下:
for tbl_name in list_of_table_names:
# Check if table exists by querying information tables
def has_table(tbl_name=tbl_name):
p = JdbcHook('conn_id')
sql =""" select count(*) from system.tables where name = '{}' """.format(tbl_name.upper())
count = p.get_records(sql)[0][0] #unpack the list/tuple
# If the query didn't return rows, branch to Create Table Task
# otherwise, branch to Dummy Operator (Airflow requires that both branches have a task)
if count == 0:
return 'tbl_create_{}'.format(tbl_name)
else:
return 'dummy_{}'.format(tbl_name)
# run has_table python function
exists = BranchPythonOperator(
task_id='tbl_exists_{}'.format(tbl_name),
python_callable=has_table,
depends_on_past=False,
dag=dag
)
# Dummy Operator
dummy = DummyOperator(task_id='dummy_{}'.format(tbl_name),dag=dag,depends_on_past=False)
# Run create table SQL script
create = JdbcOperator(
task_id='tbl_create_{}'.format(tbl_name),
jdbc_conn_id='conn_id',
sql = sql_parse(script_path, 'sql/sql_create/{}.sql'.format(tbl_name)),
depends_on_past=False,
dag = dag
)
# Run insert or truncate/replace SQL script
upsert = JdbcOperator(
task_id='tbl_upsert_{}'.format(tbl_name),
jdbc_conn_id='conn_id',
sql = sql_parse(script_path, 'sql/sql_upsert/{}.sql'.format(tbl_name)),
trigger_rule=TriggerRule.ONE_SUCCESS,
dag = dag
)
# Set dependencies
exists >> create >> upsert
exists >> dummy >> upsert
存储对在每个循环末尾添加的最后一个任务的引用。
然后,在每个循环的开头,检查ref是否存在。
如果ref存在,则将其设置为上游
大概是这样的:
last_task = None
for tbl_name in list_of_table_names:
# run has_table python function
exists = BranchPythonOperator(
task_id='tbl_exists_{}'.format(tbl_name),
python_callable=has_table,
depends_on_past=False,
dag=dag
)
if last_task:
last_task >> exists
...
# Run insert or truncate/replace SQL script
upsert = JdbcOperator(
task_id='tbl_upsert_{}'.format(tbl_name),
jdbc_conn_id='conn_id',
sql = sql_parse(script_path, 'sql/sql_upsert/{}.sql'.format(tbl_name)),
trigger_rule=TriggerRule.ONE_SUCCESS,
dag = dag
)
last_task = upsert
...