Rails的ancestry树形插件用法

parent           Returns the parent of the record, nil for a root node
parent_id        Returns the id of the parent of the record, nil for a root node
root             Returns the root of the tree the record is in, self for a root node
root_id          Returns the id of the root of the tree the record is in
is_root?         Returns true if the record is a root node, false otherwise
ancestor_ids     Returns a list of ancestor ids, starting with the root id and ending with the parent id
ancestors        Scopes the model on ancestors of the record
path_ids         Returns a list the path ids, starting with the root id and ending with the node's own id
path             Scopes model on path records of the record
children         Scopes the model on children of the record
child_ids        Returns a list of child ids
has_children?    Returns true if the record has any children, false otherwise
is_childless?    Returns true is the record has no childen, false otherwise
siblings         Scopes the model on siblings of the record, the record itself is included
sibling_ids      Returns a list of sibling ids
has_siblings?    Returns true if the record's parent has more than one child
is_only_child?   Returns true if the record is the only child of its parent
descendants      Scopes the model on direct and indirect children of the record
descendant_ids   Returns a list of a descendant ids
subtree          Scopes the model on descendants and itself
subtree_ids      Returns a list of all ids in the record's subtree
depth            Return the depth of the node, root nodes are at depth 0

参考https://github.com/stefankroes/ancestry