api/src/main/java/javax/jdo/query/Expression.java

/*
 * 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
 *
 *     https://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 javax.jdo.query;

/**
 * Representation of an expression in a query.
 *
 * @param <T> Java type being represented here
 */
public interface Expression<T> {
  /**
   * Method returning whether this expression equals the other expression.
   *
   * @param expr Other expression
   * @return Whether they are equal
   */
  BooleanExpression eq(Expression<?> expr);

  /**
   * Method returning whether this expression equals the literal.
   *
   * @param t Literal
   * @return Whether they are equal
   */
  BooleanExpression eq(T t);

  /**
   * Method returning whether this expression doesn't equal the other expression.
   *
   * @param expr Other expression
   * @return Whether they are not equal
   */
  BooleanExpression ne(Expression<?> expr);

  /**
   * Method returning whether this expression doesn't equal the literal.
   *
   * @param t literal
   * @return Whether they are not equal
   */
  BooleanExpression ne(T t);

  /**
   * Method to return a numeric expression representing the aggregated count of this expression.
   *
   * @return Numeric expression for the count
   */
  NumericExpression<Long> count();

  /**
   * Method to return a numeric expression representing the aggregated (distinct) count of this
   * expression.
   *
   * @return Numeric expression for the distinct count
   */
  NumericExpression<Long> countDistinct();

  /**
   * Return an expression for whether this expression is an instanceof the supplied class.
   *
   * @param cls Class to check against
   * @return Whether it is an instanceof
   */
  BooleanExpression instanceOf(Class<?> cls);

  /**
   * Return an expression where this expression is cast to the specified type.
   *
   * @param cls Class to cast to
   * @return The cast expression
   */
  <S> Expression<S> cast(Class<S> cls);

  /**
   * Method to return an expression with the specified alias assigned to this expression.
   *
   * @param alias the alias for this expression
   * @return the expression with an alias
   */
  Expression<T> as(String alias);
}