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core module for querydsl
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/*
 * Copyright 2011, Mysema Ltd
 * 
 * Licensed 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 com.mysema.query;

import java.util.List;
import java.util.Map;

import javax.annotation.Nonnegative;
import javax.annotation.Nullable;

import com.mysema.commons.lang.CloseableIterator;
import com.mysema.query.types.Expression;

/**
 * Projectable defines default projection methods for {@link Query} implementations.
 * All Querydsl query implementations should implement either this interface or
 * {@link SimpleProjectable}.
 *
 * @author tiwe
 * @see SimpleProjectable
 */
public interface Projectable {
    /**
     * return the amount of matched rows
     */
    @Nonnegative
    long count();

    /**
     * @return true, if rows matching the given criteria exist, otherwise false
     */
    boolean exists();

    /**
     * @return true, if no rows matching the given criteria exist, otherwise false
     */
    boolean notExists();

    /**
     * iterate over the results for the given projection
     *
     * @param args
     * @return
     */
    CloseableIterator iterate(Expression... args);

    /**
     * iterate over the results for the given projection
     *
     * @param 
     *            generic type of the Iterator
     * @param projection
     * @return an Iterator over the projection
     */
     CloseableIterator iterate(Expression projection);

    /**
     * list the results for the given projection
     * 
     * An empty list is returned for no results.
     *
     * @param args
     * @return
     */
    List list(Expression... args);

    /**
     * list the results for the given projection
     * 
     * An empty list is returned for no results.
     *
     * @param 
     *            generic type of the List
     * @param projection
     * @return a List over the projection
     */
     List list(Expression projection);

    /**
     * list the results for the given projection
     *
     * @param args
     * @return
     */
     SearchResults listResults(Expression... args);
    
    /**
     * list the results for the given projection
     *
     * @param 
     * @param projection
     * @return
     */
     SearchResults listResults(Expression projection);

    /**
     * return the given projection as a Map instance using key and value for Map population
     *
     * An empty map is returned for no results.
     *
     * @param 
     * @param 
     * @param key
     * @param value
     * @return
     */
     Map map(Expression key, Expression value);

    /**
     * return a single result for the given projection or null if no result is found
     * 
     * There is some ambiguity for missing results and null valued results, for disambiguation 
     * use the list or iterate methods instead. 
     *
     * for multiple results only the first one is returned
     *
     * @param args
     * @return
     */
    @Nullable
    Tuple singleResult(Expression... args);

    /**
     * return a single result for the given projection or null if no result is found
     *
     * There is some ambiguity for missing results and null valued results, for disambiguation 
     * use the list or iterate methods instead.
     *
     * for multiple results only the first one is returned
     *
     * @param 
     *            return type
     * @param projection
     * @return the result or null for an empty result
     */
    @Nullable
     RT singleResult(Expression projection);
    
    /**
     * Apply the given transformer to this Projectable instance and return the results
     * 
     * @param 
     * @param transformer
     * @return
     */
     T transform(ResultTransformer transformer);

    /**
     * return a unique result for the given projection or null if no result is found
     *
     * There is some ambiguity for missing results and null valued results, for disambiguation 
     * use the list or iterate methods instead.
     *
     * @param args
     * @throws NonUniqueResultException if there is more than one matching result
     * @return
     */
    @Nullable
    Tuple uniqueResult(Expression... args);

    /**
     * return a unique result for the given projection or null if no result is found
     * 
     * There is some ambiguity for missing results and null valued results, for disambiguation 
     * use the list or iterate methods instead.
     *
     * @param 
     *            return type
     * @param projection
     * @throws NonUniqueResultException if there is more than one matching result
     * @return the result or null for an empty result
     */
    @Nullable
     RT uniqueResult(Expression projection);

}