cayenne-server/src/main/java/org/apache/cayenne/query/QueryRouter.java

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package org.apache.cayenne.query;

import org.apache.cayenne.access.QueryEngine;
import org.apache.cayenne.map.DataMap;

/**
 * An interface used by Queries to route themselves to an appropriate QueryEngine. As of
 * 1.2 QueryRouter only supports routing by DataMap.
 * 
 * @since 1.2
 */
public interface QueryRouter {

    /**
     * A callback method that allows a query to set its preferred engine during the
     * routing phase. It allows query to further customize its routing, e.g. it is
     * possible to implement query chains that pass multiple queries for execution.
     * 
     * @param engine engine to use for query execution
     * @param query A query to execute.
     * @param substitutedQuery a query that was substituted for "query". Results must be
     *            mapped back to substituted query.
     */
    void route(QueryEngine engine, Query query, Query substitutedQuery);
    
    /**
     * Returns a QueryEngine for a given name. If the name is null, a default
     * QueryEngine is returned. If there's no default engine, an exception is
     * thrown.
     * 
     * @since 4.0
     */
    QueryEngine engineForName(String name);

    /**
     * Returns a QueryEngine that is configured to handle a given DataMap.
     * 
     * @throws org.apache.cayenne.CayenneRuntimeException if an engine can't be found.
     * @throws NullPointerException if a map parameter is null.
     */
    QueryEngine engineForDataMap(DataMap map);
}