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  package org.apache.cayenne.query;
  
  import java.io.Serializable;
  
  import org.apache.cayenne.access.QueryEngine;
  import org.apache.cayenne.map.DataMap;
  import org.apache.cayenne.map.EntityResolver;
  import org.apache.cayenne.map.QueryDescriptor;
  
  /**
   * Defines minimal API of a query descriptor that is executable via Cayenne.
   */
  public interface Query extends Serializable {
  
      /**
       * Returns query runtime parameters. The method is called at various stages of the
       * execution by Cayenne access stack to retrieve query parameters. EntityResolver
       * instance is passed to this method, meaning that the query doesn't need to store
       * direct references to Cayenne mapping objects and can resolve them at runtime.
       * 
       * @since 1.2
       */
      QueryMetadata getMetaData(EntityResolver resolver);
  
      /**
       * A callback method invoked by Cayenne during the routing phase of the query
       * execution. Mapping of DataNodes is provided by QueryRouter. Query should use a
       * {@link QueryRouter#route(QueryEngine, Query, Query)} callback method to route
       * itself. Query can create one or more substitute queries or even provide its own
       * QueryEngine to execute itself.
       * 
       * @since 1.2
       */
      void route(QueryRouter router, EntityResolver resolver, Query substitutedQuery);
  
      /**
       * A callback method invoked by Cayenne during the final execution phase of the query
       * run. A concrete query implementation is given a chance to decide how it should be
       * handled. Implementors can pick an appropriate method of the SQLActionVisitor to
       * handle itself, create a custom SQLAction of its own, or substitute itself with
       * another query that should be used for SQLAction construction.
       * 
       * @since 1.2
       */
      SQLAction createSQLAction(SQLActionVisitor visitor);
  }
  