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From mateiz <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-3247][SQL] An API for adding data sourc...
Date Fri, 31 Oct 2014 00:55:49 GMT
Github user mateiz commented on a diff in the pull request:

    https://github.com/apache/spark/pull/2475#discussion_r19646622
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/sources/package.scala ---
    @@ -0,0 +1,95 @@
    +/*
    + * 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
    +
    +import org.apache.spark.annotation.DeveloperApi
    +import org.apache.spark.rdd.RDD
    +import org.apache.spark.sql.catalyst.expressions.{Expression, Attribute}
    +
    +/**
    + * A set of APIs for adding data sources to Spark SQL.
    + */
    +package object sources {
    +
    +  /**
    +   * Implemented by objects that produce relations for a specific kind of data source.
 When
    +   * Spark SQL is given a DDL operation with a USING clause specified, this interface
is used to
    +   * pass in the parameters specified by a user.
    +   *
    +   * Users may specify the fully qualified class name of a given data source.  When that
class is
    +   * not found Spark SQL will append the class name `DefaultSource` to the path, allowing
for
    +   * less verbose invocation.  For example, 'org.apache.spark.sql.json' would resolve
to the
    +   * data source 'org.apache.spark.sql.json.DefaultSource'
    +   */
    +  trait RelationProvider {
    +    /** Returns a new base relation with the given parameters. */
    +    def createRelation(sqlContext: SQLContext, parameters: Map[String, String]): BaseRelation
    +  }
    +
    +  /**
    +   * Represents a collection of tuples with a known schema.  Classes that extend BaseRelation
must
    +   * be able to produce the schema of their data in the form of a [[StructType]]  In
order to be
    +   * executed, a BaseRelation must also mix in at least one of the Scan traits.
    +   *
    +   * BaseRelations must also define a equality function that only returns true when the
two
    +   * instances will return the same data.  This equality function is used when determining
when
    +   * it is safe to substitute cached results for a given relation.
    +   */
    +  @DeveloperApi
    +  abstract class BaseRelation {
    +    def sqlContext: SQLContext
    +    def schema: StructType
    +  }
    +
    +  /**
    +   * Mixed into a BaseRelation that can produce all of its tuples as an RDD of Row objects.
    +   */
    +  @DeveloperApi
    +  trait TableScan {
    +    self: BaseRelation =>
    --- End diff --
    
    I see, that seems like it's not that useful, since you can always detect whether all attributes
are selected. Abstract classes seemed easier to understand. What do other people think? @rxin
@yhuai 


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