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The Java Data Objects (JDO) API is a standard interface-based Java model abstraction of persistence, developed as Java Specification Request 243 under the auspices of the Java Community Process.
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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 javax.jdo;

import java.io.Serializable;

import javax.jdo.query.BooleanExpression;
import javax.jdo.query.CharacterExpression;
import javax.jdo.query.CollectionExpression;
import javax.jdo.query.DateExpression;
import javax.jdo.query.DateTimeExpression;
import javax.jdo.query.Expression;
import javax.jdo.query.NumericExpression;
import javax.jdo.query.PersistableExpression;
import javax.jdo.query.StringExpression;
import javax.jdo.query.TimeExpression;

/**
 * Interface for a type-safe subquery, using a fluent API.
 * Users should call methods on the subquery instance and end with a select of what the subquery returns; this
 * returns the expression that they use to link it with the owning query.
 * 
 * @param  (Candidate) type being represented
 */
public interface JDOQLTypedSubquery extends Serializable {
    /**
     * Method to return an expression for the candidate of the subquery.
     * Cast the returned expression to the candidate "Q" type to be able to call methods on it.
     * @return Expression for the candidate
     */
    PersistableExpression candidate();

    /**
     * Method to set the filter of the query.
     * @param expr Filter expression
     * @return The query
     */
    JDOQLTypedSubquery filter(BooleanExpression expr);

    /**
     * Method to set the grouping(s) for the query.
     * @param exprs Grouping expression(s)
     * @return The query
     */
    JDOQLTypedSubquery groupBy(Expression... exprs);

    /**
     * Method to set the having clause of the query.
     * @param expr Having expression
     * @return The query
     */
    JDOQLTypedSubquery having(Expression expr);

    /**
     * Accessor for the subquery (numeric) expression from the subquery when the subquery returns a single value.
     * @param expr The expression
     * @return Expression for the typesafe query
     * @param  numeric type
     */
     NumericExpression selectUnique(NumericExpression expr);

    /**
     * Accessor for the subquery (string) expression from the subquery when the subquery returns a single value.
     * @param expr The expression
     * @return Expression for the typesafe query
     */
    StringExpression selectUnique(StringExpression expr);

    /**
     * Accessor for the subquery (date) expression from the subquery when the subquery returns a single value.
     * @param expr The expression
     * @return Expression for the typesafe query
     */
    DateExpression selectUnique(DateExpression expr);

    /**
     * Accessor for the subquery (datetime) expression from the subquery when the subquery returns a single value.
     * @param expr The expression
     * @return Expression for the typesafe query
     */
    DateTimeExpression selectUnique(DateTimeExpression expr);

    /**
     * Accessor for the subquery (time) expression from the subquery when the subquery returns a single value.
     * @param expr The expression
     * @return Expression for the typesafe query
     */
    TimeExpression selectUnique(TimeExpression expr);

    /**
     * Accessor for the subquery (character) expression from the subquery when the subquery returns a single value.
     * @param expr The expression
     * @return Expression for the typesafe query
     */
    CharacterExpression selectUnique(CharacterExpression expr);

    /**
     * Accessor for the subquery (collection) expression from the subquery.
     * @param expr The expression
     * @return Expression for the typesafe query
     */
    CollectionExpression select(CollectionExpression expr);
}