Save MongoDB data to parquet file format using Apache Spark - scala

Question

I am a newbie with Apache spark as well with Scala programming language.
What I am trying to achieve is to extract the data from my local mongoDB database for then to save it in a parquet format using Apache Spark with the hadoop-connector
This is my code so far:
package com.examples
import org.apache.spark.{SparkContext, SparkConf}
import org.apache.spark.rdd.RDD
import org.apache.hadoop.conf.Configuration
import org.bson.BSONObject
import com.mongodb.hadoop.{MongoInputFormat, BSONFileInputFormat}
import org.apache.spark.sql
import org.apache.spark.sql.SQLContext
object DataMigrator {
def main(args: Array[String])
{
val conf = new SparkConf().setAppName("Migration App").setMaster("local")
val sc = new SparkContext(conf)
val sqlContext = new SQLContext(sc)
// Import statement to implicitly convert an RDD to a DataFrame
import sqlContext.implicits._
val mongoConfig = new Configuration()
mongoConfig.set("mongo.input.uri", "mongodb://localhost:27017/mongosails4.case")
val mongoRDD = sc.newAPIHadoopRDD(mongoConfig, classOf[MongoInputFormat], classOf[Object], classOf[BSONObject]);
val count = countsRDD.count()
// the count value is aprox 100,000
println("================ PRINTING =====================")
println(s"ROW COUNT IS $count")
println("================ PRINTING =====================")
}
}
The thing is that in order to save data to a parquet file format first its necessary to convert the mongoRDD variable to Spark DataFrame. I have tried something like this:
// convert RDD to DataFrame
val myDf = mongoRDD.toDF() // this lines throws an error
myDF.write.save("my/path/myData.parquet")
and the error I get is this:
Exception in thread "main" scala.MatchError: java.lang.Object (of class scala.reflect.internal.Types.$TypeRef$$anon$6)
do you guys have any other idea how could I convert the RDD to a DataFrame so that I can save data in parquet format?
Here's the structure of one Document in the mongoDB collection : https://gist.github.com/kingtrocko/83a94238304c2d654fe4

Answer 1

Create a Case class representing the data stored in your DBObject.
case class Data(x: Int, s: String)
Then, map the values of your rdd to instances of your case class.
val dataRDD = mongoRDD.values.map { obj => Data(obj.get("x"), obj.get("s")) }
Now with your RDD[Data], you can create a DataFrame with the sqlContext
val myDF = sqlContext.createDataFrame(dataRDD)
That should get you going. I can explain more later if needed.