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   *  distributed with this work for additional information
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   *  to you under the Apache License, Version 2.0 (the
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  package org.apache.cayenne.access.translator.ejbql;
  
  import java.util.Iterator;
  
  import org.apache.cayenne.ejbql.EJBQLException;
  import org.apache.cayenne.ejbql.EJBQLExpression;
  
  /**
   * @since 3.0
   */
  class EJBQLUpdateItemTranslator extends EJBQLConditionTranslator {
  
      EJBQLUpdateItemTranslator(EJBQLTranslationContext context) {
          super(context);
      }
  
      @Override
      public boolean visitPath(EJBQLExpression expression, int finishedChildIndex) {
          // unexpected, but make sure super is not called....
          return false;
      }
  
      @Override
      public boolean visitUpdateItem(EJBQLExpression expression, int finishedChildIndex) {
  
          if (finishedChildIndex == expression.getChildrenCount() - 1) {
  
              // check multicolumn match condition and undo op insertion and append it
              // from scratch if needed
              if (multiColumnOperands != null) {
  
                  if (multiColumnOperands.size() != 2) {
                      throw new EJBQLException(
                              "Invalid multi-column equals expression. Expected 2 multi-column operands, got "
                                      + multiColumnOperands.size());
                  }
  
                  context.trim(2);
  
                  EJBQLMultiColumnOperand lhs = multiColumnOperands.get(0);
                  EJBQLMultiColumnOperand rhs = multiColumnOperands.get(1);
  
                  Iterator<?> it = lhs.getKeys().iterator();
                  while (it.hasNext()) {
                      Object key = it.next();
  
                      lhs.appendValue(key);
                      context.append(" =");
                      rhs.appendValue(key);
  
                      if (it.hasNext()) {
                          context.append(',');
                      }
                  }
  
                  multiColumnOperands = null;
              }
          }
  
          return true;
      }
  
      @Override
      public boolean visitUpdateField(EJBQLExpression expression, int finishedChildIndex) {
  
          EJBQLPathTranslator pathTranslator = new EJBQLPathTranslator(context) {
  
              @Override
              protected void appendMultiColumnPath(EJBQLMultiColumnOperand operand) {
                  EJBQLUpdateItemTranslator.this.addMultiColumnOperand(operand);
              }
  
              @Override
              public boolean visitUpdateField(
                      EJBQLExpression expression,
                      int finishedChildIndex) {
                  return visitPath(expression, finishedChildIndex);
              }
          };
  
          // some DB's do not support aliases in SET (Postgresql)
          pathTranslator.setUsingAliases(false);
  
          expression.visit(pathTranslator);
          return false;
      }
  
      @Override
      public boolean visitEquals(EJBQLExpression expression, int finishedChildIndex) {
          // unlike super, Equals here has no children and is itself a child of UpdateItem
          context.append(" =");
          return false;
      }
  
      @Override
      public boolean visitUpdateValue(EJBQLExpression expression) {
  
          // a criteria for NULL is UpdateValue with no children
          if (expression.getChildrenCount() == 0) {
              context.append(" NULL");
              return false;
          }
  
          return true;
      }
  }
  