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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:

    --- Diff: flink-libraries/flink-table/src/main/java/org/apache/flink/table/annotation/ExternalCatalogCompatible.java
    @@ -0,0 +1,63 @@
    + * 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.annotation;
    +import org.apache.flink.annotation.Public;
    +import org.apache.flink.table.catalog.TableSourceConverter;
    +import java.lang.annotation.Documented;
    +import java.lang.annotation.ElementType;
    +import java.lang.annotation.Retention;
    +import java.lang.annotation.RetentionPolicy;
    +import java.lang.annotation.Target;
    + * A tableSource with this annotation represents it is compatible with external catalog,
that is,
    + * an instance of this tableSource can be converted to or converted from external catalog
    + * instance.
    + * The annotation contains the following information:
    + * <ul>
    + * <li> external catalog table type name for this kind of tableSource </li>
    + * <li> external catalog table <-> tableSource converter class </li>
    + * </ul>
    + */
    +public @interface ExternalCatalogCompatible {
    --- End diff --
    I thought about the version and agree that we do not necessarily need a dedicated version
    However, I think we need a bit more "safety" in the translation process since the converters
will rely on certain properties to be set and the link between catalog table and converter
is just a string. IMO, we need some kind of verification that the properties of a `ExternalCatalogTable`
are compatible with the requirements of a converter.
    What do you think about the following approach:
    - We extend the `TableSourceConverter` interface by a few methods to describe its requirements:
    def requiredProperties: Array[String]
    def optionalProperites: Array[String]
    def getPropertyDescription(p: String): String
    - we remove the `ExternalCatalogCompatible` annotation
    - we add a `TableType` annotation which carries a String for the table type name and which
is annotated to the `TableSourceConverter` (not to the TableSource!). 
    By doing this, we scan for converters instead of table sources. IMO, this has the benefit
that the required properties of a table type (i.e., the identifier string) are tied to the
converter, which knows how to handle the ExternalTable and convert it into a TableSource.
The type of the TableSource is not really relevant. It also means that there is one place
to go when looking for the requirements of a table type (the converter).
    What do you think @beyond1920 and @KurtYoung ?

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