ppadma commented on a change in pull request #1429: DRILL-6676: Add Union, List and Repeated List types to Result Set Loader URL: https://github.com/apache/drill/pull/1429#discussion_r211076352
########## File path: exec/vector/src/main/java/org/apache/drill/exec/vector/accessor/VariantReader.java ########## @@ -0,0 +1,115 @@ +/* + * 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.drill.exec.vector.accessor; + +import org.apache.drill.common.types.TypeProtos.MinorType; +import org.apache.drill.exec.record.metadata.VariantMetadata; + +/** + * Reader for a Drill "union vector." The union vector is presented + * as a reader over a set of variants. In the old Visual Basic world, + * "the Variant data type is a tagged union that can be used to + * represent any other data type." The term is used here to avoid + * confusion with the "union operator" which is something entirely + * different. + * <p> + * At read time, the set of possible types is fixed. A request to + * obtain a reader for an unused type returns a null pointer. + * <p> + * This reader is essentially a map of types: it allows access to + * type-specific readers for the set of types supported in the + * current vector. A client checks the type of each value, then + * uses the proper type-specific reader to access that value. + * + * @see {@link VariantWriter} + */ + +public interface VariantReader extends ColumnReader { + + VariantMetadata variantSchema(); + + int size(); + + /** + * Determine if a given type is supported by the union vector + * for some value in the result set. + * + * @param type the Drill minor type to query + * + * @return <tt>true</tt> if a reader for the given type is available, + * <tt>false</tt> if a request for a reader of that type will return + * <tt>null</tt>. + */ + + boolean hasType(MinorType type); + + /** + * Return the member reader for the given type. The type must be a member + * of the union. Allows caching readers across rows. + * + * @param type member type + * @return reader for that type + */ + + ObjectReader member(MinorType type); + + /** + * Return the scalar reader for the given type member. The type must be a + * member of the union. Allows caching readers across rows. Identical to:<br> + * <tt>>member(type).scalar()</tt> + * + * @param type member type + * @return scalar reader for that type + */ + + ScalarReader scalar(MinorType type); + + /** + * Return the data type of the current value. (What happens if the row is + * null, must it be a null of some type?) + * + * @return data type of the current data value + */ + + MinorType dataType(); + + /** + * Return the writer for the member type of the current row. Review comment: return the "reader" ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
