[jira] [Commented] (SPARK-18484) case class datasets - ability to specify decimal precision and scale

["Franco Bonazza (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-18484?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16751174#comment-16751174 ] 

Franco Bonazza commented on SPARK-18484:
----------------------------------------

What if you have a DataFrame with higher precision e.g. 38, 17, this effectively breaks df.as[TestClass], it busts on truncation because I can't specify the schema of the resulting Dataset. Am I missing something? Doesn't seem like a non issue to me. The only work around I see is not using Datasets.

> case class datasets - ability to specify decimal precision and scale
> --------------------------------------------------------------------
>
>                 Key: SPARK-18484
>                 URL: https://issues.apache.org/jira/browse/SPARK-18484
>             Project: Spark
>          Issue Type: Improvement
>    Affects Versions: 2.0.0, 2.0.1
>            Reporter: Damian Momot
>            Priority: Major
>
> Currently when using decimal type (BigDecimal in scala case class) there's no way to enforce precision and scale. This is quite critical when saving data - regarding space usage and compatibility with external systems (for example Hive table) because spark saves data as Decimal(38,18)
> {code}
> case class TestClass(id: String, money: BigDecimal)
> val testDs = spark.createDataset(Seq(
>   TestClass("1", BigDecimal("22.50")),
>   TestClass("2", BigDecimal("500.66"))
> ))
> testDs.printSchema()
> {code}
> {code}
> root
>  |-- id: string (nullable = true)
>  |-- money: decimal(38,18) (nullable = true)
> {code}
> Workaround is to convert dataset to dataframe before saving and manually cast to specific decimal scale/precision:
> {code}
> import org.apache.spark.sql.types.DecimalType
> val testDf = testDs.toDF()
> testDf
>   .withColumn("money", testDf("money").cast(DecimalType(10,2)))
>   .printSchema()
> {code}
> {code}
> root
>  |-- id: string (nullable = true)
>  |-- money: decimal(10,2) (nullable = true)
> {code}



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