missing property in dynamics treated different in asp.net?

I'm taking a look at Robs Manatee. After converting the json migrations into dynamic objects, he checks to s开发者_运维百科ee if a property exists like this:

            if (col.nullable != null) {
                if (col.nullable) {
                    sb.Append(" NULL ");
                } else {
                    sb.Append(" NOT NULL ");
                }
            } else {
                sb.Append(" NULL ");
            }

When I try to compile this into an wpf application, I get an exception on the first line:

'System.Dynamic.ExpandoObject' does not contain a definition for 'nullable'

So, why does this work when used in a asp.net setting? Or has this something to do with WebMatrix?

The issue is that webmatrix is using it's own dynamic type rather than an expando. With an expando if a value has never been set, it will throw an exception rather than return null. I'm not sure if json fx will let you use a different "expando" like this object

.net DynamicObject implementation that returns null for missing properties rather than a RunTimeBinderException

The other option is to catch the exception for a messing member.