com.dimajix.spark.sql.local.RelationProvider.scala Maven / Gradle / Ivy

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/*
 * Copyright (C) 2018 The Flowman Authors
 *
 * Licensed 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 com.dimajix.spark.sql.local

import java.nio.file.Path

import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.types.StructType


abstract class RelationProvider {
    /**
      * Returns the short name of this relation
      * @return
      */
    def shortName() : String

    /**
      * When possible, this method should return the schema of the given `files`.  When the format
      * does not support inference, or no valid files are given should return None.  In these cases
      * Spark will require that user specify the schema manually.
      */
    def inferSchema(spark: SparkSession,
                    options: Map[String, String],
                    files: Seq[Path]): Option[StructType]

    /**
      * Creates a relation for the specified parameters
      * @param spark
      * @param parameters
      * @param files - list of files to read
      * @param schema - Spark schema to use for reading/writing
      * @return
      */
    def createRelation(spark: SparkSession,
                       parameters: Map[String, String],
                       files: Seq[Path],
                       schema: StructType): BaseRelation
}