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  package org.apache.cayenne.modeler.util;
  
  import org.apache.cayenne.exp.Expression;
  import org.apache.cayenne.exp.ExpressionException;
  import org.apache.cayenne.exp.ExpressionFactory;
  import org.apache.cayenne.exp.parser.ParseException;
  import org.apache.cayenne.util.Util;
  
  /**
   * A Scope convertor that allows to display expressions in text fields.
   * 
   * @since 1.1
   */
  public class ExpressionConvertor {
  
      public String valueAsString(Object value) throws IllegalArgumentException {
          if (value == null) {
              return null;
          }
  
          if (!(value instanceof Expression)) {
              throw new IllegalArgumentException(
                  "Unsupported value class: " + value.getClass().getName());
          }
  
          return value.toString();
      }
  
      public Object stringAsValue(String string) throws IllegalArgumentException {
          if (string == null || string.trim().length() == 0) {
              return null;
          }
  
          try {
              return ExpressionFactory.exp(string);
          } catch (ExpressionException eex) {
              // this is likely a parse exception... show detailed message
              Throwable cause = Util.unwindException(eex);
              String message =
                  (cause instanceof ParseException)
                      ? cause.getMessage()
                      : "Invalid expression: " + string;
  
              throw new IllegalArgumentException(message);
          }
      }
  
      public boolean supportsStringAsValue() {
          return true;
      }
  }
  