jroof88 commented on pull request #29720:
URL: https://github.com/apache/spark/pull/29720#issuecomment-730689336
@HyukjinKwon I thought I would throw an example here for good measure:
```python
import json
from pyspark.sql.types import StructType
df = spark.sql("SELECT * FROM XXX.YYY")
schema_dict = df.schema.jsonValue()
schema_dict['fields'].append({'metadata': {'comment': 'Jacks Test Comment'},
'name': 'jacks_test_column', 'type': 'string'})
print("New Column: ", schema_dict['fields'][len(schema_dict['fields'])-1])
schema = StructType.fromJson(schema_dict)
'''
/databricks/spark/python/pyspark/sql/types.py in fromJson(cls, json)
435 return StructField(json["name"],
436 _parse_datatype_json_value(json["type"]),
--> 437 json["nullable"],
438 json["metadata"])
439
KeyError: 'nullable'
'''
```
Small Example Here where I am trying to add some metadata to a table.
I just don't really understand the statement `JSON isn't supposed to be
constructed by users` if in fact it can easily be constructed and manipulated
by the user. I would bet users manually create schemas from a variety of
sources and run into this error.
In addition, I'm happy to implement it in Scala but I would like the OK in
Python before spending time there 😄
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