Linq to SQL是否自动惰性加载关联实体？

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Linq to SQL是否自动惰性加载关联实体？

LINQ to SQL自动延迟加载关联实体吗？

我认为应该会，但我找不到一篇文章明确说明。

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是的，我相信它会自动延迟加载关联实体。它还有一个"load with"特性/语义，允许您以一次射击的方式批量加载多个内容。当您知道您需要与主实体一起立即加载相关数据时，这是非常有用的，比如预先缓存您需要呈现单个网页所需的所有数据等。

To enable lazy loading in LINQ to SQL, you need to ensure that the association property in your entity class is marked as "virtual". This allows LINQ to SQL to override the property and provide lazy loading functionality.

public class Order
{
    public int OrderId { get; set; }
    public string OrderName { get; set; }
    public virtual Customer Customer { get; set; }
}

By default, LINQ to SQL will not eagerly load associated entities. Instead, it will wait until the associated entity is explicitly accessed before loading it from the database. This can help improve performance by reducing unnecessary database queries.

If you want to load associated entities at the same time as the main entity, you can use the "load with" feature. This allows you to specify which associations should be eagerly loaded when retrieving the main entity.

var query = from o in context.Orders
            select o;
DataLoadOptions options = new DataLoadOptions();
options.LoadWith(o => o.Customer);
context.LoadOptions = options;
var orders = query.ToList();

In the above example, the "Customer" association of each order will be eagerly loaded when the orders are retrieved from the database.

Overall, LINQ to SQL provides automatic lazy loading of associated entities, but also allows you to control the eager loading behavior through the "load with" feature. This gives you flexibility in managing the loading of related data in your application.

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在LINQ to SQL中，默认情况下启用了延迟加载。通过查看这篇文章可以了解更多信息。

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在LINQ to SQL中，关联实体的加载方式取决于你如何定义“延迟加载”。

如果你使用以下代码：

var person = (from p in db.People 
              where p.PersonId = pid 
              select p).First();
var spouse = person.Spouse;

那么第二个对象（spouse）直到被引用时才会从数据库中获取，这就是“延迟加载”的实现方式。然而，这种方式需要进行两次数据库查询。

然而，如果你使用以下代码：

var family = (from p in db.People
              where p.PersonId = pid 
             select new 
              { 
                 Name = p.Name, 
                 SpouseName = p.Spouse.Name
              }).First();

LINQ会自动执行联接操作，并且在一次数据库查询中加载两个记录的信息。

因此，LINQ to SQL的“延迟加载”取决于代码中对关联实体的引用方式。如果需要避免多次数据库查询，可以使用关联查询来一次性加载所有需要的信息。

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