You must define the ParentId in the category class as nullable to use it as the foreign key property for an optional relationship: public int? ParentId { get; set; } An int property cannot take the value null and therefore cannot represent a NULL as value in a database column.
It means that T must inherit from Person<T>. This is a typical way to create type-specific methods or properties or parameters in the base class, specific to the actual descendant. For instance: public abstract class Base<T> where T : Base<T>, new() { public static T Create() { var instance = new T(); instance.Configure(42); return instance; … Read more
The easiest way: class MyModel < ActiveRecord::Base belongs_to :parent, :class_name => ‘MyModel’ has_many :children, :class_name => ‘MyModel’, :foreign_key => ‘parent_id’ end
Here’s the UNION approach I hinted at on the mailing list earlier today. from sqlalchemy import Integer, Table, Column, ForeignKey, \ create_engine, String, select from sqlalchemy.orm import Session, relationship from sqlalchemy.ext.declarative import declarative_base Base= declarative_base() friendship = Table( ‘friendships’, Base.metadata, Column(‘friend_a_id’, Integer, ForeignKey(‘users.id’), primary_key=True), Column(‘friend_b_id’, Integer, ForeignKey(‘users.id’), primary_key=True) ) class User(Base): __tablename__ = ‘users’ id … Read more
” Relative path of script file: let s:path = expand(‘<sfile>’) ” Absolute path of script file: let s:path = expand(‘<sfile>:p’) ” Absolute path of script file with symbolic links resolved: let s:path = resolve(expand(‘<sfile>:p’)) ” Folder in which script resides: (not safe for symlinks) let s:path = expand(‘<sfile>:p:h’) ” If you’re using a symlink to … Read more
import sys current_module = sys.modules[__name__]