[SQL] Add toString to DataFrame/Column

Author: Michael Armbrust <michael@databricks.com>

Closes #4436 from marmbrus/dfToString and squashes the following commits:

8a3c35f [Michael Armbrust] Merge remote-tracking branch 'origin/master' into dfToString
b72a81b [Michael Armbrust] add toString

python/pyspark/sql/dataframe.py

@@ -447,7 +447,7 @@ def selectExpr(self, *expr):
         `select` that accepts SQL expressions.
 
         >>> df.selectExpr("age * 2", "abs(age)").collect()
-        [Row(('age * 2)=4, Abs('age)=2), Row(('age * 2)=10, Abs('age)=5)]
+        [Row((age * 2)=4, Abs(age)=2), Row((age * 2)=10, Abs(age)=5)]
         """
         jexpr = ListConverter().convert(expr, self._sc._gateway._gateway_client)
         jdf = self._jdf.selectExpr(self._sc._jvm.PythonUtils.toSeq(jexpr))

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala

@@ -17,6 +17,7 @@
 
 package org.apache.spark.sql.catalyst.expressions
 
+import org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute
 import org.apache.spark.sql.catalyst.errors.TreeNodeException
 import org.apache.spark.sql.catalyst.trees
 import org.apache.spark.sql.catalyst.trees.TreeNode
@@ -66,6 +67,17 @@ abstract class Expression extends TreeNode[Expression] {
    */
   def childrenResolved = !children.exists(!_.resolved)
 
+  /**
+   * Returns a string representation of this expression that does not have developer centric
+   * debugging information like the expression id.
+   */
+  def prettyString: String = {
+    transform {
+      case a: AttributeReference => PrettyAttribute(a.name)
+      case u: UnresolvedAttribute => PrettyAttribute(u.name)
+    }.toString
+  }
+
   /**
    * A set of helper functions that return the correct descendant of `scala.math.Numeric[T]` type
    * and do any casting necessary of child evaluation.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala

@@ -190,6 +190,26 @@ case class AttributeReference(
   override def toString: String = s"$name#${exprId.id}$typeSuffix"
 }
 
+/**
+ * A place holder used when printing expressions without debugging information such as the
+ * expression id or the unresolved indicator.
+ */
+case class PrettyAttribute(name: String) extends Attribute with trees.LeafNode[Expression] {
+  type EvaluatedType = Any
+
+  override def toString = name
+
+  override def withNullability(newNullability: Boolean): Attribute = ???
+  override def newInstance(): Attribute = ???
+  override def withQualifiers(newQualifiers: Seq[String]): Attribute = ???
+  override def withName(newName: String): Attribute = ???
+  override def qualifiers: Seq[String] = ???
+  override def exprId: ExprId = ???
+  override def eval(input: Row): EvaluatedType = ???
+  override def nullable: Boolean = ???
+  override def dataType: DataType = ???
+}
+
 object VirtualColumn {
   val groupingIdName = "grouping__id"
   def newGroupingId = AttributeReference(groupingIdName, IntegerType, false)()

sql/core/src/main/scala/org/apache/spark/sql/DataFrame.scala

@@ -27,6 +27,8 @@ import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.types.StructType
 import org.apache.spark.util.Utils
 
+import scala.util.control.NonFatal
+
 
 private[sql] object DataFrame {
   def apply(sqlContext: SQLContext, logicalPlan: LogicalPlan): DataFrame = {
@@ -92,6 +94,12 @@ trait DataFrame extends RDDApi[Row] {
    */
   def toDataFrame: DataFrame = this
 
+  override def toString =
+     try schema.map(f => s"${f.name}: ${f.dataType.simpleString}").mkString("[", ", ", "]") catch {
+       case NonFatal(e) =>
+         s"Invalid tree; ${e.getMessage}:\n$queryExecution"
+     }
+
   /**
    * Returns a new [[DataFrame]] with columns renamed. This can be quite convenient in conversion
    * from a RDD of tuples into a [[DataFrame]] with meaningful names. For example:

sql/core/src/main/scala/org/apache/spark/sql/DataFrameImpl.scala

@@ -201,13 +201,11 @@ private[sql] class DataFrameImpl protected[sql](
   override def as(alias: Symbol): DataFrame = Subquery(alias.name, logicalPlan)
 
   override def select(cols: Column*): DataFrame = {
-    val exprs = cols.zipWithIndex.map {
-      case (Column(expr: NamedExpression), _) =>
-        expr
-      case (Column(expr: Expression), _) =>
-        Alias(expr, expr.toString)()
+    val namedExpressions = cols.map {
+      case Column(expr: NamedExpression) => expr
+      case Column(expr: Expression) => Alias(expr, expr.prettyString)()
     }
-    Project(exprs.toSeq, logicalPlan)
+    Project(namedExpressions.toSeq, logicalPlan)
   }
 
   override def select(col: String, cols: String*): DataFrame = {

sql/core/src/main/scala/org/apache/spark/sql/IncomputableColumn.scala

@@ -40,6 +40,8 @@ private[sql] class IncomputableColumn(protected[sql] val expr: Expression) exten
     throw new UnsupportedOperationException("Cannot run this method on an UncomputableColumn")
   }
 
+  override def toString = expr.prettyString
+
   override def isComputable: Boolean = false
 
   override val sqlContext: SQLContext = null

sql/core/src/main/scala/org/apache/spark/sql/execution/debug/package.scala

@@ -22,7 +22,7 @@ import scala.collection.mutable.HashSet
 import org.apache.spark.{AccumulatorParam, Accumulator, SparkContext}
 import org.apache.spark.annotation.DeveloperApi
 import org.apache.spark.SparkContext._
-import org.apache.spark.sql.{DataFrame, Row}
+import org.apache.spark.sql.{SQLConf, SQLContext, DataFrame, Row}
 import org.apache.spark.sql.catalyst.trees.TreeNodeRef
 import org.apache.spark.sql.types._
 
@@ -37,6 +37,15 @@ import org.apache.spark.sql.types._
  */
 package object debug {
 
+  /**
+   * Augments [[SQLContext]] with debug methods.
+   */
+  implicit class DebugSQLContext(sqlContext: SQLContext) {
+    def debug() = {
+      sqlContext.setConf(SQLConf.DATAFRAME_EAGER_ANALYSIS, "false")
+    }
+  }
+
   /**
    * :: DeveloperApi ::
    * Augments [[DataFrame]]s with debug methods.

sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala

@@ -17,6 +17,8 @@
 
 package org.apache.spark.sql
 
+import org.apache.spark.sql.TestData._
+
 import scala.language.postfixOps
 
 import org.apache.spark.sql.Dsl._
@@ -53,6 +55,33 @@ class DataFrameSuite extends QueryTest {
     TestSQLContext.setConf(SQLConf.DATAFRAME_EAGER_ANALYSIS, oldSetting.toString)
   }
 
+  test("dataframe toString") {
+    assert(testData.toString === "[key: int, value: string]")
+    assert(testData("key").toString === "[key: int]")
+  }
+
+  test("incomputable toString") {
+    assert($"test".toString === "test")
+  }
+
+  test("invalid plan toString, debug mode") {
+    val oldSetting = TestSQLContext.conf.dataFrameEagerAnalysis
+    TestSQLContext.setConf(SQLConf.DATAFRAME_EAGER_ANALYSIS, "true")
+
+    // Turn on debug mode so we can see invalid query plans.
+    import org.apache.spark.sql.execution.debug._
+    TestSQLContext.debug()
+
+    val badPlan = testData.select('badColumn)
+
+    assert(badPlan.toString contains badPlan.queryExecution.toString,
+      "toString on bad query plans should include the query execution but was:\n" +
+        badPlan.toString)
+
+    // Set the flag back to original value before this test.
+    TestSQLContext.setConf(SQLConf.DATAFRAME_EAGER_ANALYSIS, oldSetting.toString)
+  }
+
   test("table scan") {
     checkAnswer(
       testData,