public override ExpressionNode VisitCaseExpression(CaseExpression expression)
{
base.VisitCaseExpression(expression);
// NOTE: It must be a searched CASE. The normalizer should have normalized it already.
//
// Remove all WHEN expressions that are allays FALSE or NULL.
// AND
// Cut off all WHENs trailing an expression that is always true.
List <ExpressionNode> whenExpressions = new List <ExpressionNode>();
List <ExpressionNode> thenExpressions = new List <ExpressionNode>();
for (int i = 0; i < expression.WhenExpressions.Length; i++)
{
if (AstUtil.IsNull(expression.WhenExpressions[i]))
{
// A WHEN expression is always null.
continue;
}
ConstantExpression whenAsBooleanConstant = expression.WhenExpressions[i] as ConstantExpression;
if (whenAsBooleanConstant != null)
{
if (!whenAsBooleanConstant.AsBoolean)
{
// A WHEN expression is always false.
//
// We remove this part from the case expression by not adding to
// whenExpressions and thenExpressions.
continue;
}
else
{
// A WHEN expression is always true.
//
// We replace the ELSE expression by the THEN expression and
// cut off the rest.
expression.ElseExpression = expression.ThenExpressions[i];
break;
}
}
whenExpressions.Add(expression.WhenExpressions[i]);
thenExpressions.Add(expression.ThenExpressions[i]);
}
if (whenExpressions.Count == 0)
{
// This means the first WHEN expression was always false
// or all WHEN expressions are either FALSE or NULL.
//
// We replace the case expression by the else expression
// or by NULL.
if (expression.ElseExpression != null)
{
return(expression.ElseExpression);
}
return(LiteralExpression.FromTypedNull(expression.ExpressionType));
}
expression.WhenExpressions = whenExpressions.ToArray();
expression.ThenExpressions = thenExpressions.ToArray();
return(expression);
}