Coding standard for array key names

I was wondering if there is an explicit coding standard/style for array key names.

Sometimes you have arrays with keys based on sql fields/columns and sometimes you have them based on class/association names. For example, if you compute an array of results based on a collection of entities from an ORM query, is the suggested standard to name the keys under_score the same as you would for the entity properties?

Is it often completely random how arrays end up with cakephp code?