linq2sql中的简单Eager/Lazy加载示例

Question

有没有人在linq2sql中有一个简单的代码示例来演示Eager Loading和Lazy Loading之间的区别？

Answer 1

• 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,然后该集合可用于将来使用而无需其他查询:

  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
      }
  }
  

该OrderDetails只加载如果迭代,所以如果OrderDetatils从不迭代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OrderDetails为所有已检索的订单带来所有

  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