>延迟加载：对于给定的实体,它的关联集合在首次加载时可能为空,但是当首次迭代这些集合时,LINQ to sql会在加载后触发查询以加载这些集合,然后该集合可用于未来使用而不需要其他查询：

var query = from o in db.GetTable<Order>() //db is the datacontext
        select o;
foreach(Order o in query)
{
    foreach(OrderDetail d in o.OrderDetails)//Deferred loading
    {
       //Do something on these collections
    }
}

OrderDetails仅在迭代时加载,因此如果从不迭代OrderDetatils,则永远不会执行相应的查询.

> Eager Loading：立即加载所有引用实体的关联集合,例如LINQ to sql将自动为所有已检索的订单带来所有OrderDetails

DataLoadOptions op = new DataLoadOptions();
op.LoadWith<Order>(o => o.OrderDetails);
db.LoadOptions = op;
var query = from o in db.GetTable<Order>() 
         select o;
foreach(Order o in query)
{ 
    //Order details are eager loaded; additional queries are not needed
    foreach(OrderDetail d in o.OrderDetails)
    {
       //do something
    }
}

请注意：延迟执行是LINQ功能,但延迟加载是LINQ to sql功能