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BoundReference

BoundReference is a leaf expression that evaluates to a value (of the given data type) that is at the specified position in the given InternalRow.

Creating Instance

BoundReference takes the following to be created:

  • Position (ordinal)
  • Data type of values
  • nullable flag

BoundReference is created when:

Code-Generated Expression Evaluation

doGenCode(
  ctx: CodegenContext,
  ev: ExprCode): ExprCode

doGenCode is part of the Expression abstraction.

doGenCode...FIXME

import org.apache.spark.sql.catalyst.expressions.BoundReference
import org.apache.spark.sql.types.LongType
val boundRef = BoundReference(ordinal = 0, dataType = LongType, nullable = true)

// doGenCode is used when Expression.genCode is executed

import org.apache.spark.sql.catalyst.expressions.codegen.CodegenContext
val ctx = new CodegenContext
val code = boundRef.genCode(ctx).code

scala> println(code)
boolean isNull_0 = i.isNullAt(0);
long value_0 = isNull_0 ?
  -1L : (i.getLong(0));

Interpreted Expression Evaluation

eval(
  input: InternalRow): Any

eval is part of the Expression abstraction.

eval gives the value at position from the given InternalRow.

eval returns null if the value at the position is null. Otherwise, eval uses the methods of InternalRow per the defined data type to access the value.

String Representation

toString: String

toString is part of the Expression abstraction.

toString is the following text:

input[[ordinal], [dataType], [nullable]]

Catalyst DSL

Catalyst DSL's at can be used to create a BoundReference.

import org.apache.spark.sql.catalyst.dsl.expressions._
val boundRef = 'id.string.at(4)

import org.apache.spark.sql.catalyst.expressions.BoundReference
assert(boundRef.isInstanceOf[BoundReference])

Demo

import org.apache.spark.sql.catalyst.expressions.BoundReference
import org.apache.spark.sql.types.LongType
val boundRef = BoundReference(ordinal = 0, dataType = LongType, nullable = true)

scala> println(boundRef)
input[0, bigint, true]

import org.apache.spark.sql.catalyst.InternalRow
val row = InternalRow(1L, "hello")
val value = boundRef.eval(row).asInstanceOf[Long]
assert(value == 1L)