[GitHub] [spark] dongjoon-hyun commented on a change in pull request #27759: [SPARK-31008][SQL] Support json_array_length function

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

dongjoon-hyun commented on a change in pull request #27759: [SPARK-31008][SQL] Support json_array_length function
URL: https://github.com/apache/spark/pull/27759#discussion_r400587840
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
 ##########
 @@ -781,3 +781,68 @@ case class SchemaOfJson(
 
   override def prettyName: String = "schema_of_json"
 }
+
+/**
+ * A function that returns the number of elements in outer JSON array.
+ */
+@ExpressionDescription(
+  usage = "_FUNC_(jsonArray) - Returns the number of elements in outer JSON array.",
+  arguments = """
+    Arguments:
+      * jsonArray - A JSON array. An Exception is thrown if any other valid JSON strings are passed.
+          `NULL` is returned in case of invalid JSON.
+  """,
+  examples = """
+    Examples:
+      > SELECT _FUNC_('[1,2,3,4]');
+        4
+      > SELECT _FUNC_('[1,2,3,{"f1":1,"f2":[5,6]},4]');
+        5
+      > SELECT _FUNC_('[1,2');
+        NULL
+  """,
+  since = "3.1.0"
+)
+case class LengthOfJsonArray(child: Expression)
+  extends UnaryExpression with CodegenFallback {
+  override def dataType: DataType = IntegerType
+  override def nullable: Boolean = true
+  override def prettyName: String = "json_array_length"
+
+  override def eval(input: InternalRow): Any = {
+    val json = child.eval(input).asInstanceOf[UTF8String]
 
 Review comment:
   Hi, @iRakson . Please use `ExpectsInputTypes` to prevent `ClassCastException` like the following.
   ```
   spark-sql> SELECT json_array_length(1);
   20/03/30 18:19:11 ERROR SparkSQLDriver: Failed in [SELECT json_array_length(1)]
   java.lang.ClassCastException: class java.lang.Integer cannot be cast to class org.apache.spark.unsafe.types.UTF8String (java.lang.Integer is in module java.base of loader 'bootstrap'; org.apache.spark.unsafe.types.UTF8String is in unnamed module of loader 'app')
   ```

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