spark TableProvider 源码

spark TableProvider 代码

文件路径：/sql/catalyst/src/main/java/org/apache/spark/sql/connector/catalog/TableProvider.java

/*
 * 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.connector.catalog;

import java.util.Map;

import org.apache.spark.annotation.Evolving;
import org.apache.spark.sql.connector.expressions.Transform;
import org.apache.spark.sql.types.StructType;
import org.apache.spark.sql.util.CaseInsensitiveStringMap;

/**
 * The base interface for v2 data sources which don't have a real catalog. Implementations must
 * have a public, 0-arg constructor.
 * <p>
 * Note that, TableProvider can only apply data operations to existing tables, like read, append,
 * delete, and overwrite. It does not support the operations that require metadata changes, like
 * create/drop tables.
 * <p>
 * The major responsibility of this interface is to return a {@link Table} for read/write.
 * </p>
 *
 * @since 3.0.0
 */
@Evolving
public interface TableProvider {

  /**
   * Infer the schema of the table identified by the given options.
   *
   * @param options an immutable case-insensitive string-to-string map that can identify a table,
   *                e.g. file path, Kafka topic name, etc.
   */
  StructType inferSchema(CaseInsensitiveStringMap options);

  /**
   * Infer the partitioning of the table identified by the given options.
   * <p>
   * By default this method returns empty partitioning, please override it if this source support
   * partitioning.
   *
   * @param options an immutable case-insensitive string-to-string map that can identify a table,
   *                e.g. file path, Kafka topic name, etc.
   */
  default Transform[] inferPartitioning(CaseInsensitiveStringMap options) {
    return new Transform[0];
  }

  /**
   * Return a {@link Table} instance with the specified table schema, partitioning and properties
   * to do read/write. The returned table should report the same schema and partitioning with the
   * specified ones, or Spark may fail the operation.
   *
   * @param schema The specified table schema.
   * @param partitioning The specified table partitioning.
   * @param properties The specified table properties. It's case preserving (contains exactly what
   *                   users specified) and implementations are free to use it case sensitively or
   *                   insensitively. It should be able to identify a table, e.g. file path, Kafka
   *                   topic name, etc.
   */
  Table getTable(StructType schema, Transform[] partitioning, Map<String, String> properties);

  /**
   * Returns true if the source has the ability of accepting external table metadata when getting
   * tables. The external table metadata includes:
   * <ol>
   *   <li>For table reader: user-specified schema from {@code DataFrameReader}/{@code
   *   DataStreamReader} and schema/partitioning stored in Spark catalog.</li>
   *   <li>For table writer: the schema of the input {@code Dataframe} of
   *   {@code DataframeWriter}/{@code DataStreamWriter}.</li>
   * </ol>
   * <p>
   * By default this method returns false, which means the schema and partitioning passed to
   * {@link #getTable(StructType, Transform[], Map)} are from the infer methods. Please override it
   * if this source has expensive schema/partitioning inference and wants external table metadata
   * to avoid inference.
   */
  default boolean supportsExternalMetadata() {
    return false;
  }
}

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