Kafka and pyspark program: Unable to determine why dataframe is empty - apache-spark

Question

Below is my first program working with kafka and pyspark. The code seems to run without exceptions, but the output of my query is empty.
I am initiating spark and kafka. Later, in Kafka initiation, I subscribed the topic = "quickstart-events" and from terminal produced messages for this topic. But when I run this code, it gives me blank dataframes.
How do I resolve?
Code:
from pyspark import SparkContext, SparkConf
from pyspark.sql import SQLContext, SparkSession, DataFrame
from pyspark.sql.types import StructType, ArrayType, StructField, IntegerType, StringType, DoubleType
spark = SparkSession.builder \
.appName("Spark-Kafka-Integration") \
.master("local[2]") \
.getOrCreate()
dsraw = spark.readStream \
.format("kafka") \
.option("kafka.bootstrap.servers", "kafka:9092") \
.option("subscribe", "quickstart-events") \
.load()
ds = dsraw.selectExpr("CAST(key AS STRING)", "CAST(value AS STRING)")
print(type(ds))
rawQuery = dsraw \
.writeStream \
.queryName("query1")\
.format("memory")\
.start()
raw = spark.sql("select * from query1")
raw.show() # empty output
rawQuery = ds \
.writeStream \
.queryName("query2")\
.format("memory")\
.start()
raw = spark.sql("select * from query2")
raw.show() # empty output
print("complete")
Output:
+---+-----+-----+---------+------+---------+-------------+
|key|value|topic|partition|offset|timestamp|timestampType|
+---+-----+-----+---------+------+---------+-------------+
+---+-----+-----+---------+------+---------+-------------+
+---+-----+
|key|value|
+---+-----+
+---+-----+

Answer 1

if you are learning and experimenting with kafka spark streaming then it is fine.
just use:
while (True):
time.sleep(5)
print("queryresult")
raw.show() # it will start printing the result
instead of
raw.show() # it will run only once that's why not printig the result.
DO NOT USE for Production code.
Better to write like:
spark = SparkSession.builder \
.appName("Spark-Kafka-Integration") \
.master("local[2]") \
.getOrCreate()
dsraw = spark \
.readStream \
.format("kafka") \
.option("kafka.bootstrap.servers", "kafka:9092") \
.option("subscribe", "quickstart-events") \
.load()
ds = dsraw.selectExpr("CAST(key AS STRING)", "CAST(value AS STRING)")
rawQuery = \
ds \
.writeStream \
.format("console") \
.outputMode("append") \
.start()
rawQuery.awaitTermination()
it will automatically print the result on the console.