I think this model should look like:

```python
class HardwareToChassis(Base):
    # For example "mac_address"
    hardware_type = columns.Text(primary_key=True, required=True)
    # For example, an actual mac address
    hardware_id = columns.Text(primary_key=True, required=True)
    chassis_id = columns.Text(index=True,
                                            required=True,
                                            max_length=MAX_ID_LENGTH)
```

This way a lookup is just a matter of plugging in a type and a value, and getting back the chassi_id.