[GitHub] [spark] mccheah commented on a change in pull request #24560: [SPARK-27661][SQL] Add SupportsNamespaces API

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mccheah commented on a change in pull request #24560: [SPARK-27661][SQL] Add SupportsNamespaces API
URL: https://github.com/apache/spark/pull/24560#discussion_r308844618
 
 

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 File path: sql/catalyst/src/main/java/org/apache/spark/sql/catalog/v2/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.spark.sql.catalog.v2;
+
+import org.apache.spark.sql.catalyst.analysis.NamespaceAlreadyExistsException;
+import org.apache.spark.sql.catalyst.analysis.NoSuchNamespaceException;
+
+import java.util.Map;
+
+/**
+ * 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(String[])}.
+ * <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 extends CatalogPlugin {
+
+  /**
+   * Return a default namespace for the catalog.
+   * <p>
+   * When this catalog is set as the current catalog, the namespace returned by this method will be
+   * set as the current namespace.
+   * <p>
+   * The namespace returned by this method is not required to exist.
+   *
+   * @return a multi-part namespace
+   */
+  default String[] defaultNamespace() {
+    return new String[0];
+  }
+
+  /**
+   * 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 array of multi-part namespace names
+   */
+  String[][] listNamespaces() throws NoSuchNamespaceException;
+
+  /**
+   * List namespaces in a namespace.
+   * <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
+   * invoked as listNamespaces(["a"]) must return ["a", "b"] in the result array.
+   *
+   * @param namespace a multi-part namespace
+   * @return an array of multi-part namespace names
+   * @throws NoSuchNamespaceException If the namespace does not exist (optional)
+   */
+  String[][] listNamespaces(String[] namespace) throws NoSuchNamespaceException;
+
+  /**
+   * Test whether a namespace exists.
+   * <p>
+   * If an object such as a table, view, or function exists, its parent namespaces must also exist.
+   * For example, if table a.b.t exists, this method invoked as namespaceExists(["a"]) or
+   * namespaceExists(["a", "b"]) must return true.
+   *
+   * @param namespace a multi-part namespace
+   * @return true if the namespace exists, false otherwise
+   */
+  default boolean namespaceExists(String[] namespace) {
+    try {
+      loadNamespaceMetadata(namespace);
+      return true;
+    } catch (NoSuchNamespaceException e) {
+      return false;
+    }
+  }
+
+  /**
+   * Load metadata properties for a namespace.
+   *
+   * @param namespace a multi-part namespace
+   * @return a string map of properties for the given namespace
+   * @throws NoSuchNamespaceException If the namespace does not exist (optional)
+   * @throws UnsupportedOperationException If namespace properties are not supported
+   */
+  Map<String, String> loadNamespaceMetadata(String[] namespace) throws NoSuchNamespaceException;
+
+  /**
+   * Create a namespace in the catalog.
+   *
+   * @param namespace a multi-part namespace
+   * @param metadata a string map of properties for the given namespace
+   * @throws NamespaceAlreadyExistsException If the namespace already exists
+   * @throws UnsupportedOperationException If create is not a supported operation
+   */
+  void createNamespaceMetadata(
 
 Review comment:
   Instead of `createNamespaceMetadata` can we make this something like `tryCreateNamespace`, which is not required to throw an exception if the namespace already exists? Or, `getOrCreateNamespace`, for a similar effect?

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