content: /*
   * 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.calcite.schema;
  
  import org.apache.calcite.materialize.Lattice;
  import org.apache.calcite.rel.type.RelProtoDataType;
  import org.apache.calcite.schema.lookup.Lookup;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Extension to the {@link Schema} interface.
   *
   * <p>Given a user-defined schema that implements the {@link Schema} interface,
   * Calcite creates a wrapper that implements the {@code SchemaPlus} interface.
   * This provides extra functionality, such as access to tables that have been
   * added explicitly.
   *
   * <p>A user-defined schema does not need to implement this interface, but by
   * the time a schema is passed to a method in a user-defined schema or
   * user-defined table, it will have been wrapped in this interface.
   *
   * <p>SchemaPlus is intended to be used by users but not instantiated by them.
   * Users should only use the SchemaPlus they are given by the system.
   * The purpose of SchemaPlus is to expose to user code, in a read only manner,
   * some of the extra information about schemas that Calcite builds up when a
   * schema is registered. It appears in several SPI calls as context; for example
   * {@link SchemaFactory#create(SchemaPlus, String, java.util.Map)} contains a
   * parent schema that might be a wrapped instance of a user-defined
   * {@link Schema}, or indeed might not.
   */
  public interface SchemaPlus extends Schema {
  
    /**
     * Returns a lookup object to find sub schemas.
     */
    @Override Lookup<? extends SchemaPlus> subSchemas();
    /**
     * Returns the parent schema, or null if this schema has no parent.
     */
    @Nullable SchemaPlus getParentSchema();
  
    /**
     * Returns the name of this schema.
     *
     * <p>The name must not be null, and must be unique within its parent.
     * The root schema is typically named "".
     */
    String getName();
  
    // override with stricter return
    @Deprecated @Override @Nullable SchemaPlus getSubSchema(String name);
  
    /** Adds a schema as a sub-schema of this schema, and returns the wrapped
     * object. */
    SchemaPlus add(String name, Schema schema);
  
    /** Adds a table to this schema. */
    void add(String name, Table table);
  
    /** Removes a table from this schema, used e.g. to clean-up temporary tables. */
    default boolean removeTable(String name) {
      // Default implementation provided for backwards compatibility, to be removed before 2.0
      return false;
    }
  
  
    /** Adds a function to this schema. */
    void add(String name, Function function);
  
    /** Adds a type to this schema.  */
    void add(String name, RelProtoDataType type);
  
    /** Adds a lattice to this schema. */
    void add(String name, Lattice lattice);
  
    @Override boolean isMutable();
  
    /** Returns an underlying object. */
    <T extends Object> @Nullable T unwrap(Class<T> clazz);
  
    void setPath(ImmutableList<ImmutableList<String>> path);
  
    void setCacheEnabled(boolean cache);
  
    boolean isCacheEnabled();
  }
  