It doesn't look like there is any way to do it using any exposed property or method or reflection. I can suggest a couple of ways to do it.

1. Since you have the word "Date" in the column name, you can check for that word in the column name and then parse the value into a datetime.

2. You could create a user for reference that has all of the data filled in with appropriate data types then use that user's properties to get the type of the data in each column.

Can you give us an example of what values might be passed as a "not a date string"?

You should have validation on your form or whatever you are using to process the data to check the data before you attempt to save it to the database.

Hello,

You can also use the following code to get datatype of any field:

using CMS.FormEngine;
using CMS.SettingsProvider;
...

DataClassInfo dci = DataClassInfoProvider.GetDataClass("cms.user");
if (dci != null)
{
     FormInfo fi = new FormInfo(dci.ClassFormDefinition);
     FormFieldInfo ffi = fi.GetFormField("UserIsExternal");
     if (ffi != null)
      {
           FormFieldDataTypeEnum dataType = ffi.DataType;
      }
}

Best regards,
Michal Legen