Spark from_json - StructType and ArrayType - json

Question

I have a data set that comes in as XML, and one of the nodes contains JSON. Spark is reading this in as a StringType, so I am trying to use from_json() to convert the JSON to a DataFrame.
I am able to convert a string of JSON, but how do I write the schema to work with an Array?
String without Array - Working nicely
import org.apache.spark.sql.functions._
val schemaExample = new StructType()
.add("FirstName", StringType)
.add("Surname", StringType)
val dfExample = spark.sql("""select "{ \"FirstName\":\"Johnny\", \"Surname\":\"Boy\" }" as theJson""")
val dfICanWorkWith = dfExample.select(from_json($"theJson", schemaExample))
dfICanWorkWith.collect()
// Results \\
res19: Array[org.apache.spark.sql.Row] = Array([[Johnny,Boy]])
String with an Array - Can't figure this one out
import org.apache.spark.sql.functions._
val schemaExample2 = new StructType()
.add("", ArrayType(new StructType()
.add("FirstName", StringType)
.add("Surname", StringType)
)
)
val dfExample2= spark.sql("""select "[{ \"FirstName\":\"Johnny\", \"Surname\":\"Boy\" }, { \"FirstName\":\"Franky\", \"Surname\":\"Man\" }" as theJson""")
val dfICanWorkWith = dfExample2.select(from_json($"theJson", schemaExample2))
dfICanWorkWith.collect()
// Result \\
res22: Array[org.apache.spark.sql.Row] = Array([null])

Answer 1

The problem is that you don't have a fully qualified json. Your json is missing a couple of things:
First you are missing the surrounding {} in which the json is done
Second you are missing the variable value (you set it as "" but did not add it)
Lastly you are missing the closing ]
Try replacing it with:
val dfExample2= spark.sql("""select "{\"\":[{ \"FirstName\":\"Johnny\", \"Surname\":\"Boy\" }, { \"FirstName\":\"Franky\", \"Surname\":\"Man\" }]}" as theJson""")
and you will get:
scala> dfICanWorkWith.collect()
res12: Array[org.apache.spark.sql.Row] = Array([[WrappedArray([Johnny,Boy], [Franky,Man])]])

Answer 2

as of spark 2.4 the schema_of_json function helps:
> SELECT schema_of_json('[{"col":0}]');
array<struct<col:int>>
in your case you can then use the below code to parse that array of son objects:
scala> spark.sql("""select from_json("[{ \"FirstName\":\"Johnny\", \"Surname\":\"Boy\" }, { \"FirstName\":\"Franky\", \"Surname\":\"Man\" }]", 'array<struct<FirstName:string,Surname:string>>' ) as theJson""").show(false)
+------------------------------+
|theJson |
+------------------------------+
|[[Johnny, Boy], [Franky, Man]]|
+------------------------------+