There are currently some drawbacks with identifier hashing:

• They only work on one level for derived keys
• The code is suspect to high performance requirements
• Composite Keys might be suspect to weird bugs if they contain spaces.

There is a PR by goetas (https://github.com/doctrine/doctrine2/pull/232) that solves some issues, however adds a performance hit.

We should move the conditional logic of this code out and use a strategy pattern to improve both performance and robustness of this code.