Thanks for the reply, 
my situation is little different than your sample:
Following is the schema from source (df.printSchema();)

root
 |-- id: string (nullable = true)
 |-- col1: string (nullable = true)
 |-- col2: string (nullable = true)
 |-- jsonCol: string (nullable = true)

I want extract multiple fields from jsonCol to schema to be 
root
 |-- id: string (nullable = true)
 |-- col1: string (nullable = true)
 |-- col2: string (nullable = true)
 |-- jsonCol: string (nullable = true)
 |-- foo: string (nullable = true)
 |-- bar: string (nullable = true)
... 
Thanks,



On Fri, Jul 19, 2019 at 2:26 PM Mich Talebzadeh <mich.talebzadeh@gmail.com> wrote:
Hi Richard,

You can use the following to read JSON data into DF. The example is reading JSON from Kafka topic

          val sc = spark.sparkContext
         import spark.implicits._
         // Use map to create the new RDD using the value portion of the pair.
         val jsonRDD = pricesRDD.map(x => x._2)
         // Create DataFrame from jsonRDD
         val jsonDF = sqlContext.read.json(jsonRDD)


This is an example of reading a MongoDB document into Spark

dfrddMongoDB.printSchema
/*
root
 |-- _id: struct (nullable = true)
 |    |-- oid: string (nullable = true)
 |-- operation: struct (nullable = true)
 |    |-- op_type: integer (nullable = true)
 |    |-- op_time: string (nullable = true)
 |-- priceInfo: struct (nullable = true)
 |    |-- key: string (nullable = true)
 |    |-- ticker: string (nullable = true)
 |    |-- timeissued: string (nullable = true)
 |    |-- price: double (nullable = true)
 |    |-- currency: string (nullable = true)
// one example of mongo document from mongo collection
{
    "_id" : ObjectId("5cae4fa25d8b5279db785b43"),
    "priceInfo" : {
        "key" : "2ca8de24-eaf3-40d4-b0ef-c8b56534ceb5",
        "ticker" : "ORCL",
        "timeissued" : "2019-04-10T21:20:57",
        "price" : 41.13,
        "currency" : "GBP"
    },
    "operation" : {
        "op_type" : NumberInt(1),
        "op_time" : "1554927506012"
    }

}
*/
// Flatten the structs
val df = dfrddMongoDB.
               select(
                        'priceInfo.getItem("key").as("key")
                      , 'priceInfo.getItem("ticker").as("ticker")
                      , 'priceInfo.getItem("timeissued").as("timeissued")
                      , 'priceInfo.getItem("price").as("price")
                      , 'priceInfo.getItem("currency").as("currency")
                      , 'operation.getItem("op_type").as("op_type")
                      , 'operation.getItem("op_time").as("op_time")
                     )

HTH

Dr Mich Talebzadeh

 

LinkedIn  https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw

 

http://talebzadehmich.wordpress.com


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On Fri, 19 Jul 2019 at 21:48, Richard <fifistorm123@gmail.com> wrote:
let's say I use spark to migrate some data from Cassandra table to Oracle table
Cassandra Table:
CREATE TABLE SOURCE(
id UUID PRIMARY KEY,
col1 text,
col2 text,
jsonCol text
);
example jsonCol value: {"foo": "val1", "bar", "val2"}

I am trying to extract fields from the json column while importing to Oracle table 
Destination (
id varchar2(50),
col1 varchar(128).
col2 varchar(128)
raw_json clob,
foo varchar2(256),
bar varchar2(256)
);

What I have done:
separate udf for foo and bar.
This approach works, but that also means I need to deserialize raw json to json object twice, things getting worse if i want to extract many fields from the json. 
example:
df = df.withColumn("foo", getFoo.apply(col("jsonCol")))
     .withColumn("bar", getBar.apply(col("jsonCol")));
// getFoo and getBar are UserDefinedFunction

how do I parse raw json string only once and explode fields I need to multiple columns into Oracle in spark?

Thanks,