PySpark read JSON with custom nested schema doesn't apply

Question

I have this simple JSON file:

{"adas":{"parkAssist":{"rear":{"alarm":false,"muted":false},"front":{"alarm":false,"muted":false}},"lane":{"keepAssist":{"right":false,"left":false}}}}

But when I'm trying to read it like this:

spark.read.option("inferSchema", "true") \
          .option("multiline", "true") \
          .json(///myfile.json) \
          .first() \
          .asDict()

I get:

{"adas":{"parkAssist":{"rear":{"alarm":false,"muted":false},"front":{"alarm":false,"muted":false}},"lane":{"keepAssist":{"alarm":false,"muted":false}}}}

Which is wrong because adas_lane_keepAssist arguments are not correct.

If in source JSON I change one of the adas_lane_keepAssist arguments to "true", then the mapping is correct...

I also thought that maybe it's inferSchema the root of the problem, so I've made a custom_schema:

custom_schema = StructType([
    StructField("adas",StructType([
        StructField("parkAssist",StructType([
            StructField("rear",StructType([
                StructField("alarm",BooleanType(),True),
                StructField("muted",BooleanType(),True)
            ])),
            StructField("front",StructType([
                StructField("alarm",BooleanType(),True),
                StructField("muted",BooleanType(),True)
            ]))
        ])),
        StructField("lane",StructType([
            StructField("keepAssist",StructType([
                StructField("right",BooleanType(),True),
                StructField("left",BooleanType(),True)
            ]))
        ]))
    ]))
  ])

and read it like this:

spark.read.schema(custom_schema) \
          .option("multiline", "true") \
          .json(///myfile.json) \
          .first() \
          .asDict()

And I get the same wrong result:

{"adas":{"parkAssist":{"rear":{"alarm":false,"muted":false},"front":{"alarm":false,"muted":false}},"lane":{"keepAssist":{"alarm":false,"muted":false}}}}

The funny thing is if I change the order in my custom_shema like this:

custom_schema = StructType([
    StructField("adas",StructType([
        StructField("lane",StructType([
            StructField("keepAssist",StructType([
                StructField("right",BooleanType(),True),
                StructField("left",BooleanType(),True)
            ]))
        ])),
        StructField("parkAssist",StructType([
            StructField("rear",StructType([
                StructField("alarm",BooleanType(),True),
                StructField("muted",BooleanType(),True)
            ])),
            StructField("front",StructType([
                StructField("alarm",BooleanType(),True),
                StructField("muted",BooleanType(),True)
            ]))
        ]))
    ]))
  ])

Now every argument of adas_parkAssist_front/left is wrong:

{"adas":{"lane":{"keepAssist":{"right":false,"left":false}}, "parkAssist":{"rear":{"right":false,"left":false},"front":{"right":false,"left":false}}}}

Is this a limitation of PySpark?

ZygD · Accepted Answer · 2022-06-08 14:38:33Z

It's very strange to me too. I tried first, head and collect, but they all returned the same distorted structure. Before those lines, if I printed the schema, it was correct. So, the problem is in functions first, head, collect not working correctly with nested structs...

Looking for a workaround, I transformed the whole schema (which was correct after reading the JSON file) to a map type.

df = spark.read.json(r"path\test_file.json")
df = df.withColumn('adas', F.create_map(
    F.lit('lane'), F.create_map(
        F.lit('keepAssist'), F.create_map(
            F.lit('left'), F.col('adas.lane.keepAssist.left'),
            F.lit('right'), F.col('adas.lane.keepAssist.right')
        )
    ),
    F.lit('parkAssist'), F.create_map(
        F.lit('front'), F.create_map(
            F.lit('alarm'), F.col('adas.parkAssist.front.alarm'),
            F.lit('muted'), F.col('adas.parkAssist.front.muted')
        ),
        F.lit('rear'), F.create_map(
            F.lit('alarm'), F.col('adas.parkAssist.rear.alarm'),
            F.lit('muted'), F.col('adas.parkAssist.rear.muted')
        )
    )
))
print(df.head().asDict())
# {'adas': {'lane': {'keepAssist': {'left': False, 'right': False}}, 'parkAssist': {'rear': {'alarm': False, 'muted': False}, 'front': {'alarm': False, 'muted': False}}}}

Valéry · Accepted Answer · 2022-06-08 16:43:06Z

1

My spark version was 3.1.1.

After updating it to 3.2.0, the custom nested schema was read as expected.

Thx !

answered Jun 8, 2022 at 16:43

Valéry

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