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  package org.apache.cayenne.exp.parser;
  
  import java.io.IOException;
  import java.util.List;
  
  import org.apache.cayenne.ObjectId;
  import org.apache.cayenne.Persistent;
  import org.apache.cayenne.exp.Expression;
  
  /**
   * A scalar value wrapper expression.
   * 
   * @since 1.1
   */
  public class ASTScalar extends SimpleNode {
  
      protected Object value;
  
      /**
       * Constructor used by expression parser. Do not invoke directly.
       */
      ASTScalar(int id) {
          super(id);
      }
  
      public ASTScalar() {
          super(ExpressionParserTreeConstants.JJTSCALAR);
      }
  
      public ASTScalar(Object value) {
          super(ExpressionParserTreeConstants.JJTSCALAR);
          setValue(value);
      }
  
      @Override
      protected Object evaluateNode(Object o) throws Exception {
          return value;
      }
  
      /**
       * Creates a copy of this expression node, without copying children.
       */
      @Override
      public Expression shallowCopy() {
          ASTScalar copy = new ASTScalar(id);
          copy.value = value;
          return copy;
      }
  
      /**
       * @since 4.0
       */
      @Override
      public void appendAsString(Appendable out) throws IOException {
          SimpleNode.appendScalarAsString(out, value, '\"');
      }
  
      /**
       * @since 4.0
       */
      @Override
      public void appendAsEJBQL(List<Object> parameterAccumulator, Appendable out, String rootId) throws IOException {
          // TODO: see CAY-1111
          // Persistent processing is a hack for a rather special case of a single
          // column PK
          // object.. full implementation pending...
          //
          // cay1796 : change check for Persistent object by check for ObjectId
          Object scalar = value;
  
          if(scalar instanceof ObjectId) {
              ObjectId temp = (ObjectId)value;
              if (!temp.isTemporary() && temp.getIdSnapshot().size() == 1) {
                  scalar = temp.getIdSnapshot().values().iterator().next();
              }
          }
  
          SimpleNode.encodeScalarAsEJBQL(parameterAccumulator, out, scalar);
      }
  
      public void setValue(Object value) {
      	if (value instanceof Persistent){
      		this.value = ((Persistent)value).getObjectId();
      	} else {
      		this.value = value; 
      	}
      }
  
      public Object getValue() {
          return value;
      }
  
      @Override
      protected String getExpressionOperator(int index) {
          throw new UnsupportedOperationException("No operator for '" + ExpressionParserTreeConstants.jjtNodeName[id] + "'");
      }
  
      @Override
      public int getType() {
          return Expression.SCALAR;
      }
  
      @Override
      public boolean equals(Object o) {
          if (this == o) return true;
          if (o == null || getClass() != o.getClass()) return false;
          ASTScalar other = (ASTScalar) o;
          return value != null ? value.equals(other.value) : other.value == null;
      }
  
      @Override
      public int hashCode() {
          return value != null ? value.hashCode() : 0;
      }
  }
  