spark SupportsMetadataColumns 源码
spark SupportsMetadataColumns 代码
文件路径：/sql/catalyst/src/main/java/org/apache/spark/sql/connector/catalog/SupportsMetadataColumns.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 org.apache.spark.annotation.Evolving;
import org.apache.spark.sql.connector.read.SupportsPushDownRequiredColumns;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
/**
* An interface for exposing data columns for a table that are not in the table schema. For example,
* a file source could expose a "file" column that contains the path of the file that contained each
* row.
* <p>
* The columns returned by {@link #metadataColumns()} may be passed as {@link StructField} in
* requested projections. Sources that implement this interface and column projection using
* {@link SupportsPushDownRequiredColumns} must accept metadata fields passed to
* {@link SupportsPushDownRequiredColumns#pruneColumns(StructType)}.
* <p>
* If a table column and a metadata column have the same name, the metadata column will never be
* requested. It is recommended that Table implementations reject data column name that conflict
* with metadata column names.
*
* @since 3.1.0
*/
@Evolving
public interface SupportsMetadataColumns extends Table {
/**
* Metadata columns that are supported by this {@link Table}.
* <p>
* The columns returned by this method may be passed as {@link StructField} in requested
* projections using {@link SupportsPushDownRequiredColumns#pruneColumns(StructType)}.
* <p>
* If a table column and a metadata column have the same name, the metadata column will never be
* requested and is ignored. It is recommended that Table implementations reject data column names
* that conflict with metadata column names.
*
* @return an array of {@link MetadataColumn}
*/
MetadataColumn[] metadataColumns();
}
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