relationship

I'm trying to make a self-referential many-to-many relationship (it means that Line can have many parent lines and many child lines) in sqlalchemy like this: Base = declarative_base() class Association(Base): __tablename__ = 'association' prev_id = Column(Integer, ForeignKey('line.id'), primary_key=True) next_id = Column(Integer, ForeignKey('line.id'), primary_key=True) class Line(Base): __tablename__ = 'line' id = Column(Integer, primary_key = True) text = Column(Text) condition = Column(Text) action = Column(Text) next_lines = relationship(Association, backref="prev_lines") class Root(Base):

I have two models: User and HairColor. A user has only one hair color, but can have many hair color preferences. What's the best way to model this? Here's what I started to do: #models/user.rb class User < ActiveRecord::Base belongs_to :hair_color has_many :preferences, has_many :hair_colors, :through => :preferences end #models/hair_color.rb class HairColor < ActiveRecord::Base has_many :users end #models/preference.rb class Preference < ActiveRecord::Base belongs_to :user belongs_to :hair_color end Is using has_many :through the right approach? Also what if I want to extend this to other

If I have Order entity with a list of OrderDetails I can easily eager load the detail along with the order by using NHibernateUtil.Initialize(Order.Details). So obviously the NHibernate have all the information to generate the sql statement. But how do I query the database for just the Details (similar to CreateSourceQuery in Entity Framework) without manually creating a criteria? Is there something like NHibernateUtil.GetList(Order.Details)? Update: Using Darin's answer this what I finally ended up with. This is generic enough i can implement it in entity base class Dim entity as EntityBase

So I looked into neo4j, and I may be using it in an upcoming project since its data model might fit my project very well. I looked through the docs but I still need an answer to this question: Can I set relationships to be one-directional? It seems that the neo4j people like movies so let's continue with that. If I have a graph like this: Actor A -> [:Acts in] -> Movie B then direction is obvious, because the nodes are different types. But I like horror movies so... Person A -> [:wants_to_kill] -> Person B I need this relationship to be one-directional so if I query "Who does Person A want to