protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
        {
            var newField = (LuceneQueryFieldExpression)visitor.VisitExpression(QueryField);
            var newPattern = visitor.VisitExpression(QueryPattern);

            return (newPattern == QueryPattern && newField == QueryField) ? this : new LuceneQueryPredicateExpression(newField, newPattern, Occur) { AllowSpecialCharacters = AllowSpecialCharacters };
        }

    public BinaryExpressionTextGenerator (ISqlCommandBuilder commandBuilder, ExpressionTreeVisitor expressionVisitor)
    {
      ArgumentUtility.CheckNotNull ("commandBuilder", commandBuilder);
      ArgumentUtility.CheckNotNull ("expressionVisitor", expressionVisitor);

      _commandBuilder = commandBuilder;
      _expressionVisitor = expressionVisitor;

      _simpleOperatorRegistry = new Dictionary<ExpressionType, string>
                                {
                                    { ExpressionType.Add, "+" },           
                                    { ExpressionType.AddChecked, "+" },    
                                    { ExpressionType.And, "&" },           
                                    { ExpressionType.AndAlso, "AND" },     
                                    { ExpressionType.Divide, "/" },        
                                    { ExpressionType.ExclusiveOr, "^" },   
                                    { ExpressionType.GreaterThan, ">" },   
                                    { ExpressionType.GreaterThanOrEqual, ">=" }, 
                                    { ExpressionType.LessThan, "<" },            
                                    { ExpressionType.LessThanOrEqual, "<=" },    
                                    { ExpressionType.Modulo, "%" },              
                                    { ExpressionType.Multiply, "*" },            
                                    { ExpressionType.MultiplyChecked, "*" },     
                                    { ExpressionType.Or, "|" },                  
                                    { ExpressionType.OrElse, "OR" },             
                                    { ExpressionType.Subtract, "-" },            
                                    { ExpressionType.SubtractChecked, "-" },     
                                    { ExpressionType.Equal, "=" },
                                    { ExpressionType.NotEqual, "<>" }            
                                };
    }

      public CaseWhenPair VisitChildren (ExpressionTreeVisitor visitor)
      {
        var newWhen = visitor.VisitExpression (_when);
        var newThen = visitor.VisitExpression (_then);

        return Update (newWhen, newThen);
      }

 protected override Expression VisitChildren (ExpressionTreeVisitor visitor)
 {
   var newExpression = visitor.VisitExpression (_expression);
   if (newExpression != _expression)
     return new SqlExistsExpression (newExpression);
   else
     return this;
 }

		protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
		{
			var newExpression = visitor.VisitExpression(Expression);

			return newExpression != Expression
					   ? CreateNew(newExpression)
					   : this;
		}

        protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
        {
            var newExpression = visitor.VisitExpression(_operand);

            return newExpression != _operand
                ? new NotNullableExpression(newExpression)
                : this;
        }

		protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
		{
			var arguments = visitor.VisitAndConvert(Arguments, "VisitNhNew");

			return arguments != Arguments
					   ? new NhNewExpression(Members, arguments)
					   : this;
		}

 protected override Expression VisitChildren (ExpressionTreeVisitor visitor)
 {
   var newPrimaryKeyExpression = visitor.VisitExpression (_identityExpression);
   if (newPrimaryKeyExpression != _identityExpression)
     return new SqlEntityConstantExpression (Type, _value, newPrimaryKeyExpression);
   else
     return this;
 }

        protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
        {
            var newPattern = visitor.VisitExpression(pattern);

            if (Equals(pattern, newPattern)) return this;

            return new AllowSpecialCharactersExpression(newPattern);
        }

 protected override Expression VisitChildren (ExpressionTreeVisitor visitor)
 {
   var newExpressions = visitor.VisitAndConvert(_expressions, "VisitChildren");
   if (newExpressions != Expressions)
     return new SqlCompositeCustomTextGeneratorExpression (Type, newExpressions.ToArray());
   else
     return this;
 }

    public override void Generate (ISqlCommandBuilder commandBuilder, ExpressionTreeVisitor textGeneratingExpressionVisitor, ISqlGenerationStage stage)
    {
      ArgumentUtility.CheckNotNull ("commandBuilder", commandBuilder);
      ArgumentUtility.CheckNotNull ("textGeneratingExpressionVisitor", textGeneratingExpressionVisitor);
      ArgumentUtility.CheckNotNull ("stage", stage);

      textGeneratingExpressionVisitor.VisitList (_expressions, textGeneratingExpressionVisitor.VisitExpression);
    }

 protected override Expression VisitChildren (ExpressionTreeVisitor visitor)
 {
   var newColumns = visitor.VisitAndConvert (Columns, "VisitChildren");
   if (newColumns != Columns)
     return new SqlEntityDefinitionExpression (Type, TableAlias, null, IdentityExpressionGenerator, newColumns.ToArray ());
   else
     return this;
 }

 protected override Expression VisitChildren (ExpressionTreeVisitor visitor)
 {
   var newChild = visitor.VisitExpression (Child);
   if (newChild != Child)
     return new CustomCompositeExpression (Type, newChild);
   else
     return this;
 }

    public override void Generate (ISqlCommandBuilder commandBuilder, ExpressionTreeVisitor textGeneratingExpressionVisitor, ISqlGenerationStage stage)
    {
      ArgumentUtility.CheckNotNull ("commandBuilder", commandBuilder);
      ArgumentUtility.CheckNotNull ("textGeneratingExpressionVisitor", textGeneratingExpressionVisitor);
      ArgumentUtility.CheckNotNull ("stage", stage);

      commandBuilder.Append (_sqlText);
    }

		protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
		{
			var newExpression = visitor.VisitExpression(Expression);

			return newExpression != Expression
				? new NhNominatedExpression(newExpression)
				: this;
		}

 public override Expression Accept (ExpressionTreeVisitor visitor)
 {
   var specificVisitor = visitor as ISqlCustomTextGeneratorExpressionVisitor;
   if (specificVisitor != null)
     return specificVisitor.VisitSqlCustomTextGeneratorExpression (this);
   else
     return base.Accept (visitor);
 }

 public override Expression Accept (ExpressionTreeVisitor visitor)
 {
   var specificVisitor = visitor as ISqlNullCheckExpressionVisitor;
   if (specificVisitor != null)
     return specificVisitor.VisitSqlIsNotNullExpression (this);
   else
     return base.Accept (visitor);
 }

        protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
        {
            var newExpression = visitor.VisitExpression(BinaryExpression);

            if (ReferenceEquals(BinaryExpression, newExpression)) return this;

            return new BoostBinaryExpression((BinaryExpression) newExpression, Boost);
        }

 public override Expression Accept (ExpressionTreeVisitor visitor)
 {
   var specificVisitor = visitor as ISpecificVisitor;
   if (specificVisitor != null)
     return specificVisitor.VisitTestableExtensionExpression (this);
   else
     return base.Accept (visitor);
 }

        protected override Expression VisitChildren(ExpressionTreeVisitor visitor)
        {
            var newPredicate = visitor.VisitExpression(_predicate);

            return _predicate != newPredicate
                ? new DiscriminatorPredicateExpression(newPredicate, QuerySource)
                : this;
        }