Updates, Inserts, and checkboxes
When we were developing our data access objects, we added an
Update, and an Insert method, with the corresponding signatures:
Update(System.Collections.Specialized.NameValueCollection
form);
Insert(System.Collections.Specialized.NameValueCollection
form);
These methods take advantage of the fact that when you post a
form, the form values are contained in a NameValueCollection object, so you can
loop through the elements of the form, and update the respective data fields,
and then update (or insert) the database with the new values.
This scheme
is really convenient for when you want to add or remove items from the form,
because you can simply remove them from the html, without even worrying about
the backend, because those added or removed form elements are inconsequential to
the workings of the code behind. You could have a form that contained none
of the data fields, and still call these methods without any problem.
The
only problem arises when you need to deal with checkboxes.
If the user checks the checkbox, the value of the checkbox
gets submitted and the data object can be updated with the checkbox value.
However, suppose the checkbox is initially checked, and the user unchecks the
checkbox. Now, when the form is submitted, it appears as though the
checkbox never existed, because it will not be present in the
NameValueCollection, and the data object does not know to update the
appropriate value. We typically use checkboxes to denote true/false
or 1/0 values in the database, so if a user were to leave a checkbox
unchecked it means that the database value should be false or 0, but since there
is no form value present, the data object does nothing to that field.
What we did to work around this problem, was to add a hidden
form element to our forms. This hidden field is a comma separated list of
all the form elements that exist on the form. This hidden field gets
submitted with the rest of the form, and as the data object loops the form
elements, it records them. When the looping is finished, it compares the
list of form elements that it found, to the comma separated list that was
submitted with the form. If there are any form elements in the list, that
were not included in the form, then the data object knows that a checkbox was
left unchecked, and can then update the field
accordingly.
