[GitHub] [parquet-mr] shangxinli commented on a change in pull request #808: Parquet-1396: Cryptodata Interface for Schema Activation of Parquet E…

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

shangxinli commented on a change in pull request #808:
URL: https://github.com/apache/parquet-mr/pull/808#discussion_r463719447



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File path: parquet-column/src/main/java/org/apache/parquet/schema/ExtType.java
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@@ -0,0 +1,148 @@
+/*
+ * 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.parquet.schema;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * This class decorates the class 'Type' by adding a Map field 'metadata'.
+ *
+ * This decoration is needed to add metadata to each column without changing existing class 'MessageType', which is used
+ * extensively. Here is the example usage to add column metadata to schema with type of 'MessageType'.
+ *
+ * MessageType oldSchema = ...
+ * Map metadata = ...
+ * List newFields = new ArrayList();
+ * for (Type field = oldSchema.getFields()) {
+ *     Type newField = new ExtType(field);
+ *     newField.setMetadata(metadata);
+ *     newFields.add(newField);
+ * }
+ * MessageType newSchema = new MessageType(oldSchema.getName(), newFields);
+ *
+ * The implementation is mostly following decoration pattern. Most of the methods are just thin wrappers of existing
+ * implementation of PrimitiveType or GroupType.
+ */
+public class ExtType<T> extends Type {
+  private Type type;
+  private Map<String, T> metadata;
+
+  public ExtType(Type type) {
+    super(type.getName(), type.getRepetition(), type.getOriginalType(), type.getId());
+    this.type = type;
+  }
+
+  public ExtType(Type type, String name) {
+    super(name, type.getRepetition(), OriginalType.UINT_64, type.getId());
+    this.type = new PrimitiveType(type.getRepetition(), type.asPrimitiveType().getPrimitiveTypeName(), name);
+  }
+
+  public Type withId(int id) {

Review comment:
       Sounds good




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