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.linq4j;
  
  import org.apache.calcite.linq4j.tree.Expression;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.checkerframework.framework.qual.Covariant;
  
  import java.lang.reflect.Type;
  
  /**
   * Core methods that define a {@link Queryable}.
   *
   * <p>The other methods in {@link Queryable}, defined in
   * {@link ExtendedQueryable}, can easily be implemented by calling the
   * corresponding static methods in {@link Extensions}.
   *
   * @param <T> Element type
   */
  @Covariant(0)
  public interface RawQueryable<T> extends Enumerable<T> {
    /**
     * Gets the type of the element(s) that are returned when the expression
     * tree associated with this Queryable is executed.
     */
    Type getElementType();
  
    /**
     * Gets the expression tree that is associated with this Queryable.
     *
     * @return null if the expression is not available
     */
    @Nullable Expression getExpression();
  
    /**
     * Gets the query provider that is associated with this data source.
     */
    QueryProvider getProvider();
  }
  