This is somewhat academic. Most times, the default (NULL) is just fine. I’ve been talking with JJ, and he has some specific preferences–that’s what this is based on.

Usually, having a database attribute default to NULL makes it easy to check to see if a field has information. If it doesn’t, it’s just NULL–you don’t have to check for an empty string or 0.

The main reason you would want to specifically set an attribute to NOT NULL would be if it’s a field that would be used for computation. Example: you can’t multiply by NULL.

Rails makes most NULL/NOT NULL issues easier.

• Rails (Ruby) handles NULL (NIL) strings as empty strings–so it doesn’t give you errors if you’re outputting results and get a NULL. It just shows up as blank.
• Rails sets blank form fields as NULL–unlike PHP which sets them as empty. This makes it easier to check if an item has been set (as mentioned above).

NULL Database Associations

NULL associations are another matter (and not really related to this issue). You should have a way to catch Rails exceptions if you have a record with a NULL association. Example: a car model (Corvette) without a make (Chevrolet) might make your application throw up. Check for it, and handle it appropriately.

Update 2007.7.5: Handle it like this if you want an optional association:

<%=h @project.client.name rescue nil %>

Or you could just check for it with an if or unless statement:

<% unless @project.client.nil? %>

Better way?

If you have a differing opinion / think this is full of crap, please leave a comment. I’m open to suggestions on this.