Linq to Entities

多表查询如何返回查询结果：http://www.uol123.com/2011/11/29/linq-to-entity%E5%A4%9A%E8%A1%A8%E6%9F%A5%E8%AF%A2%E5%A6%82%E4%BD%95%E8%BF%94%E5%9B%9E%E6%9F%A5%E8%AF%A2%E7%BB%93%E6%9E%9C.html

EntityKey查询效率：http://wenku.baidu.com/link?url=dbhkt5EtjHTdAhdG9Q__rYcsEXPBefMZw45BECfmNiwgwtBRSBiW3a45hcMUM3Uw5_30TRVCYyYo5pQXFLzr4nJgYjXqZ77QHqvrDoz1UnW

EF教程：http://wenku.baidu.com/view/5d3ed0feaef8941ea76e053a.html

group:http://www.cnblogs.com/pato/archive/2011/03/04/1971003.html

教程2：

http://www.cnblogs.com/astar/archive/2011/01/03/1924800.html

http://www.cnblogs.com/xray2005/archive/2009/05/07/1452033.html

http://www.cnblogs.com/dudu/archive/2011/03/31/entity_framework_select_new.html

问题：

/// <summary>
    /// 用户数据交互
    /// </summary>
    public class User
    {
        private Entity.HappyOAEntities db = new Entity.HappyOAEntities();
        /// <summary>
        /// 注册新用户
        /// </summary>
        /// <param name="user"></param>
        /// <param name="login"></param>
        /// <returns></returns>
        public int Add(Entity.User user, Entity.Login login)
        {
            db.Login.AddObject(login);
            db.SaveChanges();//这里如何不先更新，下面的login.ID始终是0
            user.ID = login.ID;
            db.User.AddObject(user);
            db.SaveChanges();
            return login.ID;
        }
    }
           

解决方法： http://blog.csdn.net/wipeouter/article/details/6936425

Linq函数详细讲解：http://blog.csdn.net/xuejianwu/article/details/6931804

Linq元素累加方法，Aggregate讲解：

http://fuyu365.blog.163.com/blog/static/2491284020107192391788/

http://msdn.microsoft.com/en-us/library/system.linq.enumerable.aggregate.aspx

http://www.cnblogs.com/chenxizhang/archive/2010/01/03/1638140.html