[GitHub] [iceberg] openinx commented on a change in pull request #1235: avro: Abstract AvroWithPartnerSchemaVisitor

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

openinx commented on a change in pull request #1235:
URL: https://github.com/apache/iceberg/pull/1235#discussion_r459921033



##########
File path: core/src/main/java/org/apache/iceberg/avro/AvroWithPartnerSchemaVisitor.java
##########
@@ -0,0 +1,188 @@
+/*
+ * 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.avro;
+
+import java.util.Deque;
+import java.util.List;
+import org.apache.avro.Schema;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+
+/**
+ * A abstract avro schema visitor with partner type. This class is for both reading and writing:
+ * - For reading, the avro schema could evolve into the partner type. (schema evolution)
+ * - For writing, the avro schema should be consistent with partner type.
+ *
+ * @param <P> Partner type.
+ * @param <T> Return T.
+ */
+public abstract class AvroWithPartnerSchemaVisitor<P, T> {
+
+  public static <P, T> T visit(P partner, Schema schema, AvroWithPartnerSchemaVisitor<P, T> visitor) {
+    switch (schema.getType()) {
+      case RECORD:
+        return visitRecord(partner, schema, visitor);
+
+      case UNION:
+        return visitUnion(partner, schema, visitor);
+
+      case ARRAY:
+        return visitArray(partner, schema, visitor);
+
+      case MAP:
+        P keyType = visitor.mapKeyType(partner);
+        Preconditions.checkArgument(
+            visitor.isValidMapKey(keyType),
+            "Invalid map: %s is not a string", keyType);
+        return visitor.map(partner, schema, visit(visitor.mapValueType(partner), schema.getValueType(), visitor));
+
+      default:
+        return visitor.primitive(partner, schema);
+    }
+  }
+
+  // ---------------------------------- Static helpers ---------------------------------------------
+
+  private static <P, T> T visitRecord(P struct, Schema record, AvroWithPartnerSchemaVisitor<P, T> visitor) {
+    // check to make sure this hasn't been visited before
+    String name = record.getFullName();
+    Preconditions.checkState(!visitor.recordLevels.contains(name),
+        "Cannot process recursive Avro record %s", name);
+    List<Schema.Field> fields = record.getFields();
+    visitor.recordLevels.push(name);
+
+    List<String> names = Lists.newArrayListWithExpectedSize(fields.size());
+    List<T> results = Lists.newArrayListWithExpectedSize(fields.size());
+
+    if (visitor.schemaEvolution()) {
+      for (Schema.Field field : fields) {
+        int fieldId = AvroSchemaUtil.getFieldId(field);
+        names.add(field.name());
+        results.add(visit(visitor.structFieldTypeById(struct, fieldId), field.schema(), visitor));
+      }
+    } else {
+      String[] fieldNames = visitor.structFieldNames(struct);
+      P[] fieldTypes = visitor.structFieldTypes(struct);
+      Preconditions.checkArgument(fieldTypes.length == fields.size(),
+          "Structs do not match: %s != %s", struct, record);
+      for (int i = 0; i < fieldTypes.length; i += 1) {
+        String fieldName = fieldNames[i];
+        Schema.Field field = fields.get(i);
+        Preconditions.checkArgument(AvroSchemaUtil.makeCompatibleName(fieldName).equals(field.name()),
+            "Structs do not match: field %s != %s", fieldName, field.name());
+        results.add(visit(fieldTypes[i], field.schema(), visitor));

Review comment:
       So the difference between this sub field visit and the previous sub field [visit](https://github.com/apache/iceberg/pull/1235/files#diff-e12cc7b2561a2a909b41535f4eb86a04R78) is:  we use the different methods to get the data type of inner field.   I think we don't need both the structFieldTypeById and structFieldTypes,   is it possible to abstract them to be one method and then we could remove the `if (visitor.schemaEvolution()) {} else {...}` finally ? 




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