constraint codes should be automatically added

Last week I noticed that you can generate an error in your query simply by omitting the code from a constraint. You can see an example here: https://gist.github.com/yochannah/af2c6da36b16ea80cb771713064b00a3#file-error-md

Since the constraint codes are simply sequential uppercase characters, maybe we should generate them automatically if they're missing from a constraint, rather than requiring a human to add a new code for each constraint?