Github user rdblue commented on a diff in the pull request:
https://github.com/apache/spark/pull/21306#discussion_r200178463
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/catalog/TableChange.java
---
@@ -0,0 +1,173 @@
+/*
+ * 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.spark.sql.sources.v2.catalog;
+
+import org.apache.spark.sql.types.DataType;
+
+/**
+ * TableChange subclasses represent requested changes to a table. These
are passed to
+ * {@link DataSourceCatalog#alterTable}.
+ */
+public interface TableChange {
+
+ /**
+ * Create a TableChange for adding a top-level column to a table.
+ * <p>
+ * Because "." may be interpreted as a field path separator or may be
used in field names, it is
+ * not allowed in names passed to this method. To add to nested types or
to add fields with
+ * names that contain ".", use {@link #addColumn(String, String,
DataType)}.
+ *
+ * @param name the new top-level column name
+ * @param dataType the new column's data type
+ * @return a TableChange for the addition
+ */
+ static TableChange addColumn(String name, DataType dataType) {
+ return new AddColumn(null, name, dataType);
+ }
+
+ /**
+ * Create a TableChange for adding a nested column to a table.
+ * <p>
+ * The parent name is used to find the parent struct type where the
nested field will be added.
+ * If the parent name is null, the new column will be added to the root
as a top-level column.
+ * If parent identifies a struct, a new column is added to that struct.
If it identifies a list,
+ * the column is added to the list element struct, and if it identifies
a map, the new column is
+ * added to the map's value struct.
+ * <p>
+ * The given name is used to name the new column and names containing
"." are not handled
+ * differently.
+ *
+ * @param parent the new field's parent
+ * @param name the new field name
+ * @param dataType the new field's data type
+ * @return a TableChange for the addition
+ */
+ static TableChange addColumn(String parent, String name, DataType
dataType) {
+ return new AddColumn(parent, name, dataType);
+ }
+
+ /**
+ * Create a TableChange for renaming a field.
+ * <p>
+ * The name is used to find the field to rename. The new name will
replace the name of the type.
+ * For example, renameColumn("a.b.c", "x") should produce column a.b.x.
--- End diff --
I added an example to the Javadocs:
```scala
import TableChange._
val catalog = source.asInstanceOf[TableSupport].catalog()
catalog.alterTable(ident,
addColumn("x", IntegerType),
renameColumn("a", "b"),
deleteColumn("c")
)
```
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