[jira] [Commented] (SPARK-38826) dropFieldIfAllNull option does not work for empty JSON struct

["Apache Spark (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-38826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17519285#comment-17519285 ] 

Apache Spark commented on SPARK-38826:
--------------------------------------

User 'morvenhuang' has created a pull request for this issue:
https://github.com/apache/spark/pull/36111

> dropFieldIfAllNull option does not work for empty JSON struct
> -------------------------------------------------------------
>
>                 Key: SPARK-38826
>                 URL: https://issues.apache.org/jira/browse/SPARK-38826
>             Project: Spark
>          Issue Type: Improvement
>          Components: Documentation
>    Affects Versions: 3.2.1
>            Reporter: morvenhuang
>            Priority: Trivial
>
> As stated in the doc, 
> {quote}dropFieldIfAllNull
> Whether to ignore column of all null values or empty array/struct during schema inference.
>  
> {quote}
> But when I try this, 
>  
> {code:java}
> String json = "{\"field1\":\"value1\", \"field2\":{}}";
> JavaSparkContext jsc = new JavaSparkContext(spark.sparkContext());
> JavaRDD<String> jrdd = jsc.parallelize(Arrays.asList(json));
> Dataset<Row> df = spark.read().option("dropFieldIfAllNull", "false").json(jrdd);
> df.printSchema();
> {code}
>  
> I get this, 
> {code:java}
> root
>  |-- field1: string (nullable = true){code}
> Notice field2 is still missing even when dropFieldIfAllNull is set to false, so apparently, this option does not work for empty struct.
> This is due to SPARK-8093, the empty struct will be dropped anyway.
> I think we should update the doc, otherwise it would be confusing.
> I can make a patch for this.
>  



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