从案例类生成 Spark StructType/Schema [英] Generate a Spark StructType / Schema from a case class

问题描述

如果我想从 case class 中创建一个 StructType(即一个 DataFrame.schema)，有没有办法做到它没有创建DataFrame?我可以轻松做到:

If I wanted to create a StructType (i.e. a DataFrame.schema) out of a case class, is there a way to do it without creating a DataFrame? I can easily do:

case class TestCase(id: Long)
val schema = Seq[TestCase]().toDF.schema

但是当我想要的只是架构时，实际创建一个 DataFrame 似乎有点过分.

But it seems overkill to actually create a DataFrame when all I want is the schema.

(如果你很好奇，这个问题背后的原因是我定义了一个 UserDefinedAggregateFunction，为此你覆盖了几个返回 StructTypes 的方法和我使用案例类.)

(If you are curious, the reason behind the question is that I am defining a UserDefinedAggregateFunction, and to do so you override a couple of methods that return StructTypes and I use case classes.)

推荐答案

你也可以这样做 SQLContext.createDataFrame 做到了:

You can do it the same way SQLContext.createDataFrame does it:

import org.apache.spark.sql.catalyst.ScalaReflection
val schema = ScalaReflection.schemaFor[TestCase].dataType.asInstanceOf[StructType]

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