Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/146#discussion_r10711356
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala ---
@@ -0,0 +1,223 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql
+package catalyst
+
+import scala.language.implicitConversions
+import scala.reflect.runtime.universe.TypeTag
+
+import analysis.UnresolvedAttribute
+import expressions._
+import plans._
+import plans.logical._
+import types._
+
+/**
+ * Provides experimental support for generating catalyst schemas for scala
objects.
+ */
+object ScalaReflection {
+ import scala.reflect.runtime.universe._
+
+ /** Returns a Sequence of attributes for the given case class type. */
+ def attributesFor[T: TypeTag]: Seq[Attribute] = schemaFor[T] match {
+ case s: StructType =>
+ s.fields.map(f => AttributeReference(f.name, f.dataType, nullable =
true)())
+ }
+
+ /** Returns a catalyst DataType for the given Scala Type using
reflection. */
+ def schemaFor[T: TypeTag]: DataType = schemaFor(typeOf[T])
+
+ /** Returns a catalyst DataType for the given Scala Type using
reflection. */
+ def schemaFor(tpe: `Type`): DataType = tpe match {
+ case t if t <:< typeOf[Product] =>
+ val params = t.member("<init>": TermName).asMethod.paramss
+ StructType(
+ params.head.map(p => StructField(p.name.toString,
schemaFor(p.typeSignature), true)))
+ case t if t <:< typeOf[Seq[_]] =>
+ val TypeRef(_, _, Seq(elementType)) = t
+ ArrayType(schemaFor(elementType))
+ case t if t <:< typeOf[String] => StringType
+ case t if t <:< definitions.IntTpe => IntegerType
+ case t if t <:< definitions.LongTpe => LongType
+ case t if t <:< definitions.DoubleTpe => DoubleType
+ case t if t <:< definitions.ShortTpe => ShortType
+ case t if t <:< definitions.ByteTpe => ByteType
+ }
+
+ implicit class CaseClassRelation[A <: Product : TypeTag](data: Seq[A]) {
+
+ /**
+ * Implicitly added to Sequences of case class objects. Returns a
catalyst logical relation
+ * for the the data in the sequence.
+ */
+ def asRelation: LocalRelation = {
+ val output = attributesFor[A]
+ LocalRelation(output, data)
+ }
+ }
+}
+
+/**
+ * A collection of implicit conversions that create a DSL for constructing
catalyst data structures.
+ *
+ * {{{
+ * scala> import catalyst.dsl._
+ *
+ * // Standard operators are added to expressions.
+ * scala> Literal(1) + Literal(1)
+ * res1: catalyst.expressions.Add = (1 + 1)
+ *
+ * // There is a conversion from 'symbols to unresolved attributes.
+ * scala> 'a.attr
+ * res2: catalyst.analysis.UnresolvedAttribute = 'a
+ *
+ * // These unresolved attributes can be used to create more complicated
expressions.
+ * scala> 'a === 'b
+ * res3: catalyst.expressions.Equals = ('a = 'b)
+ *
+ * // SQL verbs can be used to construct logical query plans.
+ * scala> TestRelation('key.int, 'value.string).where('key ===
1).select('value).analyze
+ * res4: catalyst.plans.logical.LogicalPlan =
+ * Project {value#1}
+ * Filter (key#0 = 1)
+ * TestRelation {key#0,value#1}
+ * }}}
+ */
+package object dsl {
+ trait ImplicitOperators {
+ def expr: Expression
+
+ def + (other: Expression) = Add(expr, other)
+ def - (other: Expression) = Subtract(expr, other)
+ def * (other: Expression) = Multiply(expr, other)
+ def / (other: Expression) = Divide(expr, other)
+
+ def && (other: Expression) = And(expr, other)
+ def || (other: Expression) = Or(expr, other)
+
+ def < (other: Expression) = LessThan(expr, other)
+ def <= (other: Expression) = LessThanOrEqual(expr, other)
+ def > (other: Expression) = GreaterThan(expr, other)
+ def >= (other: Expression) = GreaterThanOrEqual(expr, other)
+ def === (other: Expression) = Equals(expr, other)
--- End diff --
The missing not equals is just an oversight, thanks for pointing that out!
`Not` is an expression, in [the file with other boolean
predicates](https://github.com/marmbrus/spark/blob/catalyst/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala).
It is not clear to me yet if we want to expose these directly or not to the
user. I'm hesitant to make too much of catalyst a Public API, especially
initially.
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