[GitHub] [iceberg] JonasJ-ap commented on a diff in pull request #6449: WIP: Core, Spark: Adding support for Migrating Delta Lake Table to Iceberg Table

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

JonasJ-ap commented on code in PR #6449:
URL: https://github.com/apache/iceberg/pull/6449#discussion_r1054932981


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core/src/main/java/org/apache/iceberg/DeltaLakeDataTypeVisitor.java:
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@@ -0,0 +1,74 @@
+/*
+ * 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;
+
+import io.delta.standalone.types.ArrayType;
+import io.delta.standalone.types.DataType;
+import io.delta.standalone.types.MapType;
+import io.delta.standalone.types.StructField;
+import io.delta.standalone.types.StructType;
+import java.util.List;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+
+public class DeltaLakeDataTypeVisitor<T> {
+  public static <T> T visit(DataType type, DeltaLakeDataTypeVisitor<T> visitor) {
+    if (type instanceof StructType) {
+      StructField[] fields = ((StructType) type).getFields();
+      List<T> fieldResults = Lists.newArrayListWithExpectedSize(fields.length);
+
+      for (StructField field : fields) {
+        fieldResults.add(visitor.field(field, visit(field.getDataType(), visitor)));
+      }
+
+      return visitor.struct((StructType) type, fieldResults);
+
+    } else if (type instanceof MapType) {
+      return visitor.map(
+          (MapType) type,
+          visit(((MapType) type).getKeyType(), visitor),
+          visit(((MapType) type).getValueType(), visitor));
+
+    } else if (type instanceof ArrayType) {
+      return visitor.array((ArrayType) type, visit(((ArrayType) type).getElementType(), visitor));
+
+    } else {
+      return visitor.atomic(type);
+    }
+  }
+
+  public T struct(StructType struct, List<T> fieldResults) {
+    return null;

Review Comment:
   The actual implementations of these functions are higly dependent on the actual type we want to convert to. I think maybe we can make these methods abstract and make actual implementation in `DeltaLakeTypeToType`. Do you think it is ok to implement in this way?



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