Right! My bad!

Looking at this more closely, it seems that supporting STI is a bit trickier. Either 1) the item_type column would need to take the model instance's inheritence_column (type) value (i.e. Bravo) rather than Alpha, otherwise 2) there would need to be another indexed column. I like (1) however that means that if you change the type value of an instance, it's history is going to be fragmented. 

Adding the column seems a bit much but STI is kind of important. 

Thoughts?