[jira] [Created] (SPARK-19849) Support ArrayType in to_json function/expression

["Hyukjin Kwon (JIRA)" <ji...@apache.org>]

Hyukjin Kwon created SPARK-19849:
------------------------------------

             Summary: Support ArrayType in to_json function/expression
                 Key: SPARK-19849
                 URL: https://issues.apache.org/jira/browse/SPARK-19849
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 2.2.0
            Reporter: Hyukjin Kwon


After SPARK-19595, we could

{code}
import org.apache.spark.sql.functions._
import org.apache.spark.sql.types._
val schema = ArrayType(StructType(StructField("a", IntegerType) :: Nil))
Seq(("""[{"a": 1}, {"a": 2}]""")).toDF("array").select(from_json(col("array"), schema)).show()
{code}

Maybe, it'd be better if we provide a way to read it back via {{to_json}} as below:

{code}
import org.apache.spark.sql.functions._
import org.apache.spark.sql.types._

val schema = ArrayType(StructType(StructField("a", IntegerType) :: Nil))
val df = Seq("""[{"a":1}, {"a":2}]""").toDF("json").select(from_json($"json", schema).as("array"))
df.show()

// Read back.
df.select(to_json($"array").as("json")).show()
{code}

{code}

+----------+
|     array|
+----------+
|[[1], [2]]|
+----------+

+-----------------+
|             json|
+-----------------+
|[{"a":1},{"a":2}]|
+-----------------+
{code}

Currently, it throws an exception as below:

{code}
org.apache.spark.sql.AnalysisException: cannot resolve 'structtojson(`array`)' due to data type mismatch: structtojson requires that the expression is a struct expression.;;
'Project [structtojson(array#30, Some(Asia/Seoul)) AS structtojson(array)#45]
+- Project [jsontostruct(ArrayType(StructType(StructField(a,IntegerType,true)),true), array#27, Some(Asia/Seoul)) AS array#30]
   +- Project [value#25 AS array#27]
      +- LocalRelation [value#25]

  at org.apache.spark.sql.catalyst.analysis.package$AnalysisErrorAt.failAnalysis(package.scala:42)
  at org.apache.spark.sql.catalyst.analysis.CheckAnalysis$$anonfun$checkAnalysis$1$$anonfun$apply$2.applyOrElse(CheckAnalysis.scala:80)
  at org.apache.spark.sql.catalyst.analysis.CheckAnalysis$$anonfun$checkAnalysis$1$$anonfun$apply$2.applyOrElse(CheckAnalysis.scala:72)
{code}



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