/// <summary>
/// Evaluates the specified expression.
/// </summary>
/// <param name="expression">The expression to evaluate.</param>
/// <returns>Value of the expression.</returns>
public QueryValue Visit(QueryIsNullExpression expression)
{
// Cannot be a collection
ExceptionUtilities.Assert(!(expression.Argument.ExpressionType is QueryCollectionType), "IsNull expression cannot be a collection");
var argument = this.Evaluate(expression.Argument);
return(argument.Type.EvaluationStrategy.BooleanType.CreateValue(argument.IsNull));
}
/// <summary>
/// Replaces the given expression.
/// </summary>
/// <param name="expression">Expression to replace.</param>
/// <returns>Replaced expression.</returns>
public QueryExpression Visit(QueryIsNullExpression expression)
{
var argument = this.ReplaceExpression(expression.Argument);
if (this.HasChanged(expression.Argument, argument))
{
return(new QueryIsNullExpression(argument, expression.ExpressionType));
}
else
{
return(expression);
}
}
/// <summary>
/// Visits a QueryExpression tree whose root node is the QueryIsNullExpression.
/// </summary>
/// <param name="expression">The root node of the expression tree being visited.</param>
/// <returns>Uri query string representing the expression.</returns>
public override string Visit(QueryIsNullExpression expression)
{
string argument = this.Convert(expression.Argument);
return string.Format(CultureInfo.InvariantCulture, "{0} eq null", argument);
}
/// <summary>
/// Visits a QueryExpression tree whose root node is the QueryIsNullExpression.
/// </summary>
/// <param name="expression">The root node of the expression tree being visited.</param>
/// <returns>Uri query string representing the expression.</returns>
public virtual string Visit(QueryIsNullExpression expression)
{
throw new TaupoNotSupportedException("Not supported");
}
/// <summary>
/// Resolves types for the specified expression.
/// </summary>
/// <param name="expression">The expression to resolve types for.</param>
/// <returns>Expression with resolved types.</returns>
public QueryExpression Visit(QueryIsNullExpression expression)
{
var argument = this.ResolveTypes(expression.Argument);
return(new QueryIsNullExpression(argument, this.EvaluationStrategy.BooleanType));
}
/// <summary>
/// Generates System.CodeDom.CodeExpression from the given expression.
/// </summary>
/// <param name="expression">Expression from which System.CodeDom.CodeExpression is generated.</param>
/// <returns>Generated System.CodeDom.CodeExpression.</returns>
public virtual CodeExpression Visit(QueryIsNullExpression expression)
{
var argument = this.GenerateCode(expression.Argument);
return(Code.ValueEquals(argument, Code.Null()));
}
/// <summary>
/// Visits a QueryExpression tree whose root node is the QueryIsNullExpression.
/// </summary>
/// <param name="expression">The root node of the expression tree being visited.</param>
/// <returns>Uri query string representing the expression.</returns>
public override string Visit(QueryIsNullExpression expression)
{
string argument = this.Convert(expression.Argument);
return(string.Format(CultureInfo.InvariantCulture, "{0} eq null", argument));
}
