[GitHub] [incubator-iceberg] rdblue commented on a change in pull request #227: ORC column map fix

[GitBox <gi...@apache.org>]

rdblue commented on a change in pull request #227: ORC column map fix
URL: https://github.com/apache/incubator-iceberg/pull/227#discussion_r300056977
 
 

 ##########
 File path: orc/src/main/java/org/apache/iceberg/orc/ORCSchemaUtil.java
 ##########
 @@ -0,0 +1,89 @@
+/*
+ * 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.iceberg.orc;
+
+import com.google.common.base.Splitter;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.util.IdentityHashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+import org.apache.orc.TypeDescription;
+
+/**
+ * Utilities for mapping Iceberg to ORC schemas.
+ */
+final class ORCSchemaUtil {
+
+  private ORCSchemaUtil() {}
+
+  static Map<TypeDescription, IcebergColumn> newColumMap() {
+    return new IdentityHashMap<>();
+  }
+
+  static <K, V> Map<K, V> inverse(Map<V, K> mapToFlip) {
+    return mapToFlip.entrySet()
+        .stream()
+        .collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
+  }
+
+  /**
+   * Serializes the column mapping into a comma separated list of values in the form:
+   * <code>
+   *   orc_id:iceberg_id:(required|optional),orc_id:iceberg_id:(required|optional),...
+   * </code>
+   * For example:
+   * <code>
+   *   0:2:required,1:3:optional
+   * </code>
+   * The above example defines two column mappings:
+   * - ORC column 0 maps to Iceberg column 2 and it's required.
+   * - ORC column 1 maps to Iceberg column 3 and it's optiona.
+   * @param idMap the Map with the column mapping of ORC type to Iceberg column.
 
 Review comment:
   Nit: typo in "optiona", and there should be an empty line between docs and `@param`.

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