ActsAsDAG

add_parent      Adds the given record(s) as a parent of the receiver. Accepts multiple arguments or an array.
add_child       Adds the given record(s) as a child of the receiver. Accepts multiple arguments or an array.
remove_parent   Removes the given record as a parent of the receiver. Accepts a single record.
remove_child    Removes the given record as a child of the receiver. Accepts a single record.

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
parent_of?       Returns true if the record is the parent of the given node, false otherwise
parents?         Returns true if the record has any parents, false otherwise
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
ancestor_of?     Returns true if the record is the ancestor of the given node, false otherwise
ancestors?       Returns true if the record has any ancestors, false otherwise
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
child_of?        Returns true if the record is the child of the given node, false otherwise
children?        Returns true if the record has any children, false otherwise
descendants      Scopes the model on direct and indirect children of the record
descendant_ids   Returns a list of a descendant ids
descendant_of?   Returns true if the record is the descendant of the given node, false otherwise
descendants?     Returns true if the record has any descendants, false otherwise
subtree          Scopes the model on descendants and itself
subtree_ids      Returns a list of all ids in the record's subtree
distance_to      Returns the minimum number of ancestors/descendants between two records, e.g. child.distance_to(grandpa) #=> 2

roots                   Nodes without parents
leaves                  Nodes without children
ancestors_of(node)      Ancestors of node, node can be either a record, id, scope, or array
children_of(node)       Children of node, node can be either a record, id, scope, or array
descendants_of(node)    Descendants of node, node can be either a record, id, scope, or array
path_of(node)           Node and ancestors of node, node can be either a record, id, scope, or array
subtree_of(node)        Subtree of node, node can be either a record, id, scope, or array

:link_class             The name of the class to use for storing parent-child relationships. Defaults to "#{self.name}Link", e.g. PersonLink
:link_table             The table the link class stores data in. Defaults to "acts_as_dag_links"
:descendant_class       The name of the class to use for storing ancestor-descendant relationships. Defaults to "#{self.name}Descendant", e.g PersonDescendant
:descendant_table       The table the descendant class stores data in. Defaults to "acts_as_dag_descendants"
:link_conditions        Conditions to use when fetching link and descendant records. Defaults to {:category_type => self.name}, e.g. {:category_type => 'Person'}

remove_parent   Removes the given record(s) as a parent of the receiver. Accepts a multiple arguments or an array.
remove_child    Removes the given record(s) as a child of the receiver. Accepts a multiple arguments or an array.

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
has_children?    Returns true if the record has any children, false otherwise
is_childless?    Returns true is the record has no children, 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
depth            Return the depth of the node, root nodes are at depth 0

siblings_of(node)       Siblings of node, node can be either a record or an id