def single(self):
nodes = super(One, self).all()<EOL>if nodes:<EOL><INDENT>if len(nodes) == <NUM_LIT:1>:<EOL><INDENT>return nodes[<NUM_LIT:0>]<EOL><DEDENT>else:<EOL><INDENT>raise CardinalityViolation(self, len(nodes))<EOL><DEDENT><DEDENT>else:<EOL><INDENT>raise CardinalityViolation(self, '<STR_LIT:none>')<EOL><DEDENT>
Return the associated node.

:return: node