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UnresolvedGenerator Expression

UnresolvedGenerator is a[Generator] that represents an unresolved generator in a logical query plan.

UnresolvedGenerator is <> exclusively when AstBuilder is requested to[withGenerate] (as part of[Generate] logical operator) for SQL's LATERAL VIEW (in SELECT or FROM clauses).

[source, scala]

// SQLs borrowed from val sqlText = """ SELECT pageid, adid FROM pageAds LATERAL VIEW explode(adid_list) adTable AS adid """ // Register pageAds table Seq( ("front_page", Array(1, 2, 3)), ("contact_page", Array(3, 4, 5))) .toDF("pageid", "adid_list") .createOrReplaceTempView("pageAds") val query = sql(sqlText) val logicalPlan = query.queryExecution.logical scala> println(logicalPlan.numberedTreeString) 00 'Project ['pageid, 'adid] 01 +- 'Generate 'explode('adid_list), false, adtable, ['adid] 02 +- 'UnresolvedRelation pageAds

import org.apache.spark.sql.catalyst.plans.logical.Generate val generator = logicalPlan.collectFirst { case g: Generate => g.generator }.get

scala> :type generator org.apache.spark.sql.catalyst.expressions.Generator

import org.apache.spark.sql.catalyst.analysis.UnresolvedGenerator scala> generator.isInstanceOf[UnresolvedGenerator] res1: Boolean = true

[[resolved]] UnresolvedGenerator can never be[resolved] (and is replaced at <>).

[[Unevaluable]][[eval]][[doGenCode]] Given UnresolvedGenerator can never be resolved it should not come as a surprise that it[cannot be evaluated] either (i.e. produce a value given an internal row). When requested to evaluate, UnresolvedGenerator simply reports a UnsupportedOperationException.

Cannot evaluate expression: [this]

[[analysis-phase]] [NOTE] ==== UnresolvedGenerator is resolved to a concrete[Generator] expression when ResolveFunctions logical resolution rule is executed. ====

NOTE: UnresolvedGenerator is similar to[UnresolvedFunction] and differs mostly by the type (to make Spark development with Scala easier?)

=== [[creating-instance]] Creating UnresolvedGenerator Instance

UnresolvedGenerator takes the following when created:

  • [[name]] FunctionIdentifier
  • [[children]] Child[expressions]

Last update: 2020-11-07