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Posted to commits@airflow.apache.org by GitBox <gi...@apache.org> on 2021/08/15 22:38:11 UTC
[GitHub] [airflow] iblaine opened a new pull request #17628: Create cols in df object so we avoid exception when no rows returned
iblaine opened a new pull request #17628:
URL: https://github.com/apache/airflow/pull/17628
Improves get_pandas_df() in HiveServer2Hook by properly adding columns when an empty dataframe is encountered.
Currently in hive hooks, when get_pandas_df() is used to create a dataframe, the next step is to add columns to the existing dataframe object. pandas throws an exception when trying to add columns to an empty dataframe with no columns. By moving adding columns to the step where the dataframe is created, we can avoid throwing an exception on empty dataframes.
Current behavior using get_pandas_df() to read and an empty table:
```
hh = HiveServer2Hook()
sql = "SELECT * FROM <table> WHERE 1=0"
df = hh.get_pandas_df(sql)
[2021-08-15 21:10:15,282] {{hive.py:449}} INFO - SELECT * FROM <table> WHERE 1=0
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
File "/venv/lib/python3.7/site-packages/airflow/providers/apache/hive/hooks/hive.py", line 1073, in get_pandas_df
df.columns = [c[0] for c in res['header']]
File "/venv/lib/python3.7/site-packages/pandas/core/generic.py", line 5154, in __setattr__
return object.__setattr__(self, name, value)
File "pandas/_libs/properties.pyx", line 66, in pandas._libs.properties.AxisProperty.__set__
File "/venv/lib/python3.7/site-packages/pandas/core/generic.py", line 564, in _set_axis
self._mgr.set_axis(axis, labels)
File "/venv/lib/python3.7/site-packages/pandas/core/internals/managers.py", line 227, in set_axis
f"Length mismatch: Expected axis has {old_len} elements, new "
ValueError: Length mismatch: Expected axis has 0 elements, new values have 1 elements
```
New behavior w/this PR
```
hh = HiveServer2Hook()
sql = "SELECT * FROM <table> WHERE 1=0"
df = hh.get_pandas_df(sql)
len(df.index)
0
```
I need help testing this against the `airflow.static_babynames` hive table, if that test is needed. Also curious how to set that up. I have tested this locally against my own hive server & it is working as expected.
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[GitHub] [airflow] iblaine closed pull request #17628: Create cols in df object so we avoid exception when no rows returned
Posted by GitBox <gi...@apache.org>.
iblaine closed pull request #17628:
URL: https://github.com/apache/airflow/pull/17628
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[GitHub] [airflow] boring-cyborg[bot] commented on pull request #17628: Create cols in df object so we avoid exception when no rows returned
Posted by GitBox <gi...@apache.org>.
boring-cyborg[bot] commented on pull request #17628:
URL: https://github.com/apache/airflow/pull/17628#issuecomment-899119914
Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/main/CONTRIBUTING.rst)
Here are some useful points:
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[GitHub] [airflow] iblaine commented on pull request #17628: Create cols in df object so we avoid exception when no rows returned
Posted by GitBox <gi...@apache.org>.
iblaine commented on pull request #17628:
URL: https://github.com/apache/airflow/pull/17628#issuecomment-899242604
Closing PR, will open up a new PR on the main branch.
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