StructField — Single Field in StructType¶

[[creating-instance]] StructField describes a single field in a StructType with the following:

• [[name]] Name
• [[dataType]] DataType
• [[nullable]] nullable flag (enabled by default)
• [[metadata]] Metadata (empty by default)

A comment is part of metadata under comment key and is used to build a Hive column or when describing a table.

[source, scala]¶

scala> schemaTyped("a").getComment res0: Option[String] = None

scala> schemaTyped("a").withComment("this is a comment").getComment res1: Option[String] = Some(this is a comment)

As of Spark 2.4.0, StructField can be converted to DDL format using <> method.

.Example: Using StructField.toDDL [source, scala]

import org.apache.spark.sql.types.MetadataBuilder val metadata = new MetadataBuilder() .putString("comment", "this is a comment") .build import org.apache.spark.sql.types.{LongType, StructField} val f = new StructField(name = "id", dataType = LongType, nullable = false, metadata) scala> println(f.toDDL) id BIGINT COMMENT 'this is a comment'

=== [[toDDL]] Converting to DDL Format -- toDDL Method

[source, scala]¶

toDDL: String¶

toDDL gives a text in the format:

[quoted name] [dataType][optional comment]

toDDL is used when:

• StructType is requested to convert itself to DDL format
• ShowCreateTableCommand logical command is executed