public function getOneByKey($key)
	{
		// Note: this switch exists like this because PHP does not have "traditional method overloading".
		switch(gettype($key))
		{
			// Use EntityIdentifier to retrieve.
			case 'object':
				return $this->getOneByIdentifier($key);
			break;

			// Use a composite key to retrieve.
			case 'array':
				return $this->getOneByCompoundKey($key);
			break;

			// Use an actual Identifier string to retrieve.
			case 'string':
				return $this->getOneByUuid($key);
			break;

			// Use Entity to retrieve.
			default:
				return new Payload($key, 'invalid_key_type');
		}
	}