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  package org.apache.cayenne.access.translator.ejbql;
  
  import org.apache.cayenne.ejbql.EJBQLBaseVisitor;
  import org.apache.cayenne.ejbql.EJBQLExpression;
  
  /**
   * A translator of EJBQL SELECT statements into SQL.
   * 
   * @since 3.0
   */
  public class EJBQLSelectTranslator extends EJBQLBaseVisitor {
  
      protected EJBQLTranslationContext context;
  
      protected EJBQLSelectTranslator(EJBQLTranslationContext context) {
          this.context = context;
      }
  
      EJBQLTranslationContext getContext() {
          return context;
      }
  
      @Override
      public boolean visitDistinct(EJBQLExpression expression) {
          // "distinct" is appended via a marker as sometimes a later match on to-many would
          // require a DISTINCT insertion.
          context.pushMarker(context.makeDistinctMarker(), true);
          context.append(" DISTINCT");
          context.popMarker();
          return true;
      }
  
      @Override
      public boolean visitFrom(EJBQLExpression expression, int finishedChildIndex) {
          context.append(" FROM");
          context.setAppendingResultColumns(false);
          expression.visit(context.getTranslatorFactory().getFromTranslator(context));
          context.markCurrentPosition(context.makeWhereMarker());
          context.markCurrentPosition(context.makeEntityQualifierMarker());
          return false;
      }
  
      @Override
      public boolean visitGroupBy(EJBQLExpression expression) {
          context.append(" GROUP BY");
          expression.visit(context.getTranslatorFactory().getGroupByTranslator(context));
          return false;
      }
  
      @Override
      public boolean visitHaving(EJBQLExpression expression) {
          context.append(" HAVING");
          expression.visit(context.getTranslatorFactory().getConditionTranslator(context));
          return false;
      }
  
      @Override
      public boolean visitOrderBy(EJBQLExpression expression) {
          context.append(" ORDER BY");
          expression.visit(context.getTranslatorFactory().getOrderByTranslator(context));
          return false;
      }
  
      @Override
      public boolean visitSelect(EJBQLExpression expression) {
          // this ensures that result columns are appeneded only in top-level select, but
          // not subselect (as 'visitSelect' is not called on subselect)
          context.setAppendingResultColumns(true);
          return true;
      }
  
      @Override
      public boolean visitSelectClause(EJBQLExpression expression) {
          context.append("SELECT");
          context.markCurrentPosition(context.makeDistinctMarker());
          return true;
      }
  
      @Override
      public boolean visitSelectExpressions(EJBQLExpression expression) {
          expression.visit(context.getTranslatorFactory().getSelectColumnsTranslator(
                  context));
          return false;
      }
  
      @Override
      public boolean visitWhere(EJBQLExpression expression) {
          // "WHERE" is appended via a marker as it may have been already appended when an
          // entity inheritance qualifier was applied.
          context.pushMarker(context.makeWhereMarker(), true);
          context.append(" WHERE");
          context.popMarker();
  
          if (context.findOrCreateMarkedBuffer(context.makeEntityQualifierMarker()).length() > 0) {
              context.append(" AND");
          }
  
          expression.visit(context.getTranslatorFactory().getConditionTranslator(context));
          return false;
      }
  
  }
  