[GitHub] [incubator-iceberg] rdblue commented on a change in pull request #919: [ISSUE #672] Add SupportsNamespaces on HiveCatalog and HadoopCatalog

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rdblue commented on a change in pull request #919: [ISSUE #672] Add SupportsNamespaces on HiveCatalog and HadoopCatalog
URL: https://github.com/apache/incubator-iceberg/pull/919#discussion_r407669291
 
 

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 File path: api/src/main/java/org/apache/iceberg/catalog/SupportsNamespaces.java
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+/*
+ * 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.catalog;
+
+import com.google.common.collect.ImmutableMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.iceberg.exceptions.AlreadyExistsException;
+import org.apache.iceberg.exceptions.NoSuchNamespaceException;
+
+/**
+ * Catalog methods for working with namespaces.
+ * <p>
+ * If an object such as a table, view, or function exists, its parent namespaces must also exist
+ * and must be returned by the discovery methods {@link #listNamespaces()} and
+ * {@link #listNamespaces(Namespace namespace)}.
+ * <p>
+ * Catalog implementations are not required to maintain the existence of namespaces independent of
+ * objects in a namespace. For example, a function catalog that loads functions using reflection
+ * and uses Java packages as namespaces is not required to support the methods to create, alter, or
+ * drop a namespace. Implementations are allowed to discover the existence of objects or namespaces
+ * without throwing {@link NoSuchNamespaceException} when no namespace is found.
+ */
+public interface SupportsNamespaces {
+  /**
+   * Create a namespace in the catalog.
+   *
+   * @param namespace {@link Namespace}.
+   * @throws AlreadyExistsException If the namespace already exists
+   * @throws UnsupportedOperationException If create is not a supported operation
+   */
+  default void createNamespace(Namespace namespace) {
+    createNamespace(namespace, ImmutableMap.of());
+  }
+
+  /**
+   * Create a namespace in the catalog.
+   *
+   * @param namespace a multi-part namespace
+   * @param metadata a string ImmutableMap of properties for the given namespace
+   * @throws AlreadyExistsException If the namespace already exists
+   * @throws UnsupportedOperationException If create is not a supported operation
+   */
+  void createNamespace(Namespace namespace, ImmutableMap<String, String> metadata);
+
+  /**
+   * List top-level namespaces from the catalog.
+   * <p>
+   * If an object such as a table, view, or function exists, its parent namespaces must also exist
+   * and must be returned by this discovery method. For example, if table a.b.t exists, this method
+   * must return ["a"] in the result array.
+   *
+   * @return an List of namespace {@link Namespace} names
+   */
+  default List<Namespace> listNamespaces() {
+    return listNamespaces(Namespace.empty());
+  }
+
+  /**
+   * List  namespaces from the namespace.
+   * <p>
+   * For example, if table a.b.t exists, use 'SELECT NAMESPACE IN a' this method
+   * must return Namepace.of("a","b") {@link Namespace}.
+   *
+   * @return an List of namespace {@link Namespace} names
+   * @throws NoSuchNamespaceException If the namespace does not exist (optional)
+   */
+  List<Namespace> listNamespaces(Namespace namespace) throws NoSuchNamespaceException;
+
+  /**
+   * Load metadata properties for a namespace.
+   *
+   * @param namespace a Namespace.of(name) {@link Namespace}
+   * @return a string map of properties for the given namespace
+   * @throws NoSuchNamespaceException If the namespace does not exist (optional)
+   */
+  Map<String, String> loadNamespaceMetadata(Namespace namespace) throws NoSuchNamespaceException;
+
+  /**
+   * Drop namespace, while the namespace haven't table or sub namespace will return true.
+   *
+   * @param namespace a Namespace.of(name) {@link Namespace}
+   * @return true while drop success.
+   * @throws NoSuchNamespaceException If the namespace does not exist (optional)
+   */
+  boolean dropNamespace(Namespace namespace) throws NoSuchNamespaceException;
+
+  /**
+   * Apply a set of metadata changes to a namespace in the catalog.
+   *
+   * @param namespace a Namespace.of(name) {@link Namespace}
+   * @param changes a collection of changes to apply to the namespace
+   * @throws NoSuchNamespaceException If the namespace does not exist (optional)
+   * @throws UnsupportedOperationException If namespace properties are not supported
+   */
+  boolean alterNamespace(Namespace namespace, NamespaceChange... changes) throws NoSuchNamespaceException;
 
 Review comment:
   Do you think there will be changes to a namespace other than setting properties and removing properties?
   
   It may be much simpler to use `setProperties(Namespace, Map<String, String>)` and `removeProperties(Namespace, Set<String>)` instead of this and the `NamespaceChange` classes. What do you think?

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