If you have db/dataset and db/dataset/dev folders that contain yml files, you can upload yml data to your db as follows:
However, if you load dev data with the following command, it nukes the db data from the previous command:
rake db:dataset:load DATASET=dev
Thus, you can run the following command to add dev data without nuking the existing data:
rake db:dataset:add DATASET=dev
Or if you have dev data first and wants to load db/dataset without nuking db/dataset/dev, you need to run the following:
rake db:dataset:add DATASET=.