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Collection Query Engine: NoSQL indexing and query engine for Java collections with ultra-low latency
There is a newer version: 3.6.0
/**
 * Copyright 2012-2015 Niall Gallagher
 *
 * 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.googlecode.cqengine.index.support;

import com.googlecode.cqengine.attribute.Attribute;
import com.googlecode.cqengine.attribute.SimpleAttribute;
import com.googlecode.cqengine.attribute.SimpleNullableAttribute;
import com.googlecode.cqengine.query.Query;
import com.googlecode.cqengine.query.option.DeduplicationOption;
import com.googlecode.cqengine.query.option.QueryOptions;
import com.googlecode.cqengine.query.simple.In;
import com.googlecode.cqengine.resultset.ResultSet;
import com.googlecode.cqengine.resultset.connective.ResultSetUnion;
import com.googlecode.cqengine.resultset.connective.ResultSetUnionAll;
import com.googlecode.cqengine.resultset.stored.StoredResultSet;

/**
 *  Index utilities
 *
 * @author Silvano Riz
 */
public class IndexSupport {

    private IndexSupport(){}

    /**
     * 
 If a query option specifying logical deduplication was supplied, wrap the given result sets in {@link ResultSetUnion}, otherwise wrap in {@link ResultSetUnionAll}.
     *
     * 
 There are two exceptions where a {@link ResultSetUnionAll} is used regardless of the logical deduplication query option:
     * 

     *     
     *         If the index is built on a SimpleAttribute which means that the same object could not exist in more than one {@link StoredResultSet}.
     *     
     *     
     *         If the query is an {@link In} query and it is marked as disjoint ( {@link In#isDisjoint()} returns true )
     *     
     * 
     *
     * @param results Provides the result sets to union
     * @param query The query for which the union is being constructed
     * @param queryOptions Specifies whether or not logical deduplication is required
     * @param retrievalCost The resultSet retrieval cost
     * @return A union view over the given result sets
     */
    public static  ResultSet deduplicateIfNecessary(final Iterable> results,
                                                             final Query query,
                                                             final Attribute attribute,
                                                             final QueryOptions queryOptions,
                                                             final int retrievalCost) {
        boolean logicalElimination = DeduplicationOption.isLogicalElimination(queryOptions);
        boolean attributeHasAtMostOneValue = (attribute instanceof SimpleAttribute || attribute instanceof SimpleNullableAttribute);
        boolean queryIsADisjointInQuery = query instanceof In && ((In) query).isDisjoint();
        if (!logicalElimination || attributeHasAtMostOneValue || queryIsADisjointInQuery) {
            // No need to deduplicate...
            return new ResultSetUnionAll(results, query, queryOptions) {
                @Override
                public int getRetrievalCost() {
                    return retrievalCost;
                }
            };
        } else {
            // We need to deduplicate...
            return new ResultSetUnion(results, query, queryOptions) {
                @Override
                public int getRetrievalCost() {
                    return retrievalCost;
                }
            };
        }
    }

}