[GitHub] [flink] twalthr commented on a change in pull request #17313: [FLINK-16204][table] Support JSON_ARRAY()

[GitBox <gi...@apache.org>]

twalthr commented on a change in pull request #17313:
URL: https://github.com/apache/flink/pull/17313#discussion_r720075675



##########
File path: flink-table/flink-table-api-scala/src/main/scala/org/apache/flink/table/api/ImplicitExpressionConversions.scala
##########
@@ -811,8 +815,45 @@ trait ImplicitExpressionConversions {
    * // {"K1":{"K2":"V"}}
    * jsonObject(JsonOnNull.NULL, "K1", jsonObject(JsonOnNull.NULL, "K2", "V"))
    * }}}
+   *
+   * @see #jsonObject
    */
   def jsonObject(onNull: JsonOnNull, keyValues: Any*): Expression = {
     Expressions.jsonObject(onNull, keyValues)
   }
+
+  /**
+   * Builds a JSON array string from a list of values.
+   *
+   * This function returns a JSON string. The values can be arbitrary expressions. The
+   * [[JsonOnNull onNull]] behavior defines how to treat `NULL` values.
+   *
+   * Elements which are created from another JSON construction function call
+   * (`jsonObject`, `jsonArray`) are inserted directly rather than as a string. This allows
+   * building nested JSON structures.
+   *
+   * Examples:
+   *
+   * {{{
+   * // "[]"
+   * jsonArray(JsonOnNull.NULL)
+   * // "[1,\"2\"]"
+   * jsonArray(JsonOnNull.NULL, 1, "2")
+   *
+   * // Expressions as values
+   * jsonArray(JsonOnNull.NULL, $("orderId"))
+   *
+   * // ON NULL
+   * jsonArray(JsonOnNull.NULL, nullOf(DataTypes.STRING()))   // "[null]"
+   * jsonArray(JsonOnNull.ABSENT, nullOf(DataTypes.STRING())) // "[]"
+   *
+   * // "[[1]]"
+   * jsonArray(JsonOnNull.NULL, jsonArray(JsonOnNull.NULL, 1))
+   * }}}
+   *
+   * @see #jsonObject
+   */
+  def jsonArray(onNull: JsonOnNull, values: Any*): Expression = {

Review comment:
       `keyValues` should be `Expression*` to trigger Scala's implicit conversions

##########
File path: flink-table/flink-table-api-scala/src/main/scala/org/apache/flink/table/api/ImplicitExpressionConversions.scala
##########
@@ -811,8 +815,45 @@ trait ImplicitExpressionConversions {
    * // {"K1":{"K2":"V"}}
    * jsonObject(JsonOnNull.NULL, "K1", jsonObject(JsonOnNull.NULL, "K2", "V"))
    * }}}
+   *
+   * @see #jsonObject
    */
   def jsonObject(onNull: JsonOnNull, keyValues: Any*): Expression = {

Review comment:
       `keyValues` should be `Expression*` to trigger Scala's implicit conversions

##########
File path: flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/planner/codegen/JsonGenerateUtils.scala
##########
@@ -31,12 +31,27 @@ import org.apache.flink.shaded.jackson2.com.fasterxml.jackson.databind.node.{Arr
 import org.apache.flink.shaded.jackson2.com.fasterxml.jackson.databind.util.RawValue
 
 import org.apache.calcite.rex.{RexCall, RexNode}
+import org.apache.calcite.sql.SqlJsonConstructorNullClause
 
 import java.time.format.DateTimeFormatter
 
 /** Utility for generating JSON function calls. */
 object JsonGenerateUtils {
 
+  /** Returns a term which wraps the given <code>expression</code> into a [[JsonNode]]. If the

Review comment:
       nit: `<code>` is not Scala




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