The Default Debacle

As I continue my study of RubyOnRails using Build Your Own Ruby On Rails Web Applications by Patrick Lenz, I'm including expansions on certain topics that piqued my interest. First, here are a few useful links if you're reading the book too.

book web site

book errata

ruby on rails docs

Today I diverged from the examples in the book again and encountered an issue with the word 'default'. It turns out that default is a SQL keyword depending on the context of the expression it is used in. I wanted to store a default value for a record in a table. This is illustrated in the table below:

user	default	actual
tom	sleep	sleep
bob	awake	sleep
susy	awake	awake

The table tracks the 'default' or usual state of each user and their current 'actual' state. This seemed simple enough. The add_column call in my migration file had no problem with the column name 'default'. However, when I tried to add items to the table, the column name 'default' caused an SQL error. This is because the word 'default' can have a special meaning in an insert query.

There may be a way to escape 'default' so that it's accepted as a column name, but I don't know what it is. (If you do, please comment! Thanks!) So, the simple path seemed to be to just rename the column. But... when I used rename_column, I also received SQL errors. The solution that finally worked was to first use remove_column to get rid of the column all together. Fortunately since insert didn't like 'default' there was no data in the column to worry about deleting. I then added the column default_value using the add_column call.

Just to be on the safe side, I did not implement the opposite of add_column in the self.down method of the migration file.

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