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From fhueske <...@git.apache.org>
Subject [GitHub] flink pull request #3406: [flink-5568] [Table API & SQL]Introduce interface ...
Date Thu, 09 Mar 2017 14:46:32 GMT
Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3406#discussion_r105141214
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/catalog/ExternalCatalogSchema.scala
---
    @@ -0,0 +1,164 @@
    +/*
    + * 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.flink.table.catalog
    +
    +import java.util
    +
    +import org.apache.calcite.linq4j.tree.Expression
    +import org.apache.calcite.schema._
    +import org.apache.flink.table.api.{DatabaseNotExistException, TableNotExistException}
    +import org.slf4j.{Logger, LoggerFactory}
    +
    +import scala.collection.JavaConverters._
    +
    +/**
    +  * This class is responsible for connect external catalog to calcite catalog.
    +  * In this way, it is possible to look-up and access tables in SQL queries
    +  * without registering tables in advance.
    +  * The databases in the external catalog registers as calcite sub-Schemas of current
schema.
    +  * The tables in a given database registers as calcite tables
    +  * of the [[ExternalCatalogDatabaseSchema]].
    +  *
    +  * @param catalogIdentifier external catalog name
    +  * @param catalog           external catalog
    +  */
    +class ExternalCatalogSchema(
    +    catalogIdentifier: String,
    +    catalog: ExternalCatalog) extends Schema {
    +
    +  private val LOG: Logger = LoggerFactory.getLogger(this.getClass)
    +
    +  /**
    +    * Looks up database by the given sub-schema name in the external catalog,
    +    * returns it Wrapped in a [[ExternalCatalogDatabaseSchema]] with the given database
name.
    +    *
    +    * @param name Sub-schema name
    +    * @return Sub-schema with a given name, or null
    +    */
    +  override def getSubSchema(name: String): Schema = {
    +    try {
    +      val db = catalog.getDatabase(name)
    --- End diff --
    
    Shouldn't we specify the behavior of `getDatabase()` more clearly? 
    Is it expected to return `null` or throw an exception if the database does not exist?
Right now we cover both cases which is not necessary if we have a clear interface definition.


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