SparkR DataFrame fail to return data of Decimal type

[Shkurenko, Alex]

Got an issue similar to https://issues.apache.org/jira/browse/SPARK-8897,
but with the Decimal datatype coming from a Postgres DB:

//Set up SparkR

>Sys.setenv(SPARK_HOME="/Users/ashkurenko/work/git_repos/spark")
>Sys.setenv(SPARKR_SUBMIT_ARGS="--driver-class-path
~/Downloads/postgresql-9.4-1201.jdbc4.jar sparkr-shell")
>.libPaths(c(file.path(Sys.getenv("SPARK_HOME"), "R", "lib"), .libPaths()))
>library(SparkR)
>sc <- sparkR.init(master="local")

// Connect to a Postgres DB via JDBC
>sqlContext <- sparkRSQL.init(sc)
>sql(sqlContext, "
    CREATE TEMPORARY TABLE mytable
    USING org.apache.spark.sql.jdbc
    OPTIONS (url 'jdbc:postgresql://servername:5432/dbname'
    ,dbtable 'mydbtable'
)
")

// Try pulling a Decimal column from a table
>myDataFrame <- sql(sqlContext,("select a_decimal_column  from mytable "))

// The schema shows up fine

>show(myDataFrame)

DataFrame[a_decimal_column:decimal(10,0)]

>schema(myDataFrame)

StructType
|-name = "a_decimal_column", type = "DecimalType(10,0)", nullable = TRUE

// ... but pulling data fails:

localDF <- collect(myDataFrame)

Error in as.data.frame.default(x[[i]], optional = TRUE) :
  cannot coerce class ""jobj"" to a data.frame


-------
Proposed fix:

diff --git a/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
b/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
index d5b4260..b77ae2a 100644
--- a/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
+++ b/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
@@ -219,6 +219,9 @@ private[spark] object SerDe {
         case "float" | "java.lang.Float" =>
           writeType(dos, "double")
           writeDouble(dos, value.asInstanceOf[Float].toDouble)
+        case "decimal" | "java.math.BigDecimal" =>
+           writeType(dos, "double")
+           writeDouble(dos,
scala.math.BigDecimal(value.asInstanceOf[java.math.BigDecimal]).toDouble)
         case "double" | "java.lang.Double" =>
           writeType(dos, "double")
           writeDouble(dos, value.asInstanceOf[Double])

Thanks,
Alex