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  package org.apache.cayenne.query;
  
  import org.apache.cayenne.CayenneRuntimeException;
  import org.apache.cayenne.map.DataMap;
  import org.apache.cayenne.map.EntityResolver;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  
  /**
   * A Query decorator for a collection of other queries. Note that QueryChain will always
   * return DataRows (that is if it returns data), as it has no way of knowing how to
   * convert the results to objects.
   * 
   * @since 1.2
   */
  public class QueryChain implements Query {
  
      protected Collection<Query> chain;
  
      /**
       * Creates an empty QueryChain.
       */
      public QueryChain() {
      }
  
      /**
       * Creates a new QueryChain out of an array of queries.
       */
      public QueryChain(Query[] queries) {
          if (queries != null && queries.length > 0) {
              this.chain = new ArrayList<>(Arrays.asList(queries));
          }
      }
  
      /**
       * Creates a new QueryChain with a collection of Queries.
       */
      public QueryChain(Collection<? extends Query> queries) {
          if (queries != null && !queries.isEmpty()) {
              this.chain = new ArrayList<>(queries);
          }
      }
  
      /**
       * Adds a query to the chain.
       */
      public void addQuery(Query query) {
          if (chain == null) {
              chain = new ArrayList<>();
          }
  
          chain.add(query);
      }
  
      /**
       * Removes a query from the chain, returning true if the query was indeed present in
       * the chain and was removed.
       */
      public boolean removeQuery(Query query) {
          return (chain != null) && chain.remove(query);
      }
  
      public boolean isEmpty() {
          return chain == null || chain.isEmpty();
      }
  
      /**
       * Delegates routing to each individual query in the chain. If there is no queries,
       * this method does nothing.
       */
      public void route(QueryRouter router, EntityResolver resolver, Query substitutedQuery) {
          if (chain != null && !chain.isEmpty()) {
              for (Query q : chain) {
                  q.route(router, resolver, substitutedQuery);
              }
          }
      }
  
      /**
       * Throws an exception as execution should've been delegated to the queries contained
       * in the chain.
       */
      public SQLAction createSQLAction(SQLActionVisitor visitor) {
          throw new CayenneRuntimeException("Chain doesn't support its own execution "
                  + "and should've been split into separate queries during routing phase.");
      }
  
      /**
       * Returns default metadata.
       */
      public QueryMetadata getMetaData(EntityResolver resolver) {
          QueryMetadataWrapper wrapper = new QueryMetadataWrapper(DefaultQueryMetadata.defaultMetadata);
          wrapper.override(QueryMetadata.FETCHING_DATA_ROWS_PROPERTY, Boolean.TRUE);
          return wrapper;
      }
  }
  