Hello Brian,

Right now, MapType is not supported in the StructType provided to jsonRDD/jsonFile. We will add the support. I have created https://issues.apache.org/jira/browse/SPARK-4302 to track this issue.



On Fri, Nov 7, 2014 at 3:41 PM, boclair <boclair@gmail.com> wrote:
I'm loading json into spark to create a schemaRDD (sqlContext.jsonRDD(..)).
I'd like some of the json fields to be in a MapType rather than a sub
StructType, as the keys will be very sparse.

For example:
> val sqlContext = new org.apache.spark.sql.SQLContext(sc)
> import sqlContext.createSchemaRDD
> val jsonRdd = sc.parallelize(Seq("""{"key": "1234", "attributes":
> {"gender": "m"}}""",
                                                   """{"key": "4321",
"attributes": {"location": "nyc"}}"""))
> val schemaRdd = sqlContext.jsonRDD(jsonRdd)
> schemaRdd.printSchema
 |-- attributes: struct (nullable = true)
 |    |-- gender: string (nullable = true)
 |    |-- location: string (nullable = true)
 |-- key: string (nullable = true)
> schemaRdd.collect
res1: Array[org.apache.spark.sql.Row] = Array([[m,null],1234],

However this isn't what I want.  So I created my own StructType to pass to
the jsonRDD call:

> import org.apache.spark.sql._
> val st = StructType(Seq(StructField("key", StringType, false),
MapType(StringType, StringType, false))))
> val jsonRddSt = sc.parallelize(Seq("""{"key": "1234", "attributes":
> {"gender": "m"}}""",
                                                      """{"key": "4321",
"attributes": {"location": "nyc"}}"""))
> val schemaRddSt = sqlContext.jsonRDD(jsonRddSt, st)
> schemaRddSt.printSchema
 |-- key: string (nullable = false)
 |-- attributes: map (nullable = true)
 |    |-- key: string
 |    |-- value: string (valueContainsNull = false)
> schemaRddSt.collect
***  Failure  ***
scala.MatchError: MapType(StringType,StringType,false) (of class
        at org.apache.spark.sql.json.JsonRDD$.enforceCorrectType(JsonRDD.scala:397)

The schema of the schemaRDD is correct.  But it seems that the json cannot
be coerced to a MapType.  I can see at the line in the stack trace that
there is no case statement for MapType.  Is there something I'm missing?  Is
this a bug or decision to not support MapType with json?


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