我使用带有LINQ的NHibernate 3.2,在SQL中进行n+1个查询。在映射中使用fetch设置为“join”。当我使用criteria时,只有一个select查询。此外,我找不到一些例子中看到的Fetch()
或FetchMany()
方法。是否存在使用Linq to NHibernate 3.2解决n+1问题的方法?
我的代码简化版本如下:
class News
{
public virtual int Id { get; protected set; }
public virtual DateTime Date { get; set; }
public virtual Category Category { get; set; }
}
class Category
{
public virtual int Id { get; protected set; }
public virtual ISet<News> News { get; set; }
}
映射:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="News" namespace="NewsManagement.Models">
<class name="News" table="News">
<id name="Id">
<generator class="native" />
</id>
<property name="Date" not-null="true" />
<many-to-one name="Category" fetch="join" column="CategoryId" class="Category, NHibernateManyToOne" not-null="true"/>
</class>
</hibernate-mapping>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="News" namespace="NewsManagement.Models">
<class name="Category" table="Categories">
<id name="Id" column="Id">
<generator class="native" />
</id>
<set name="News" fetch="join" cascade="all-delete-orphan">
<key column="CategoryId" />
<one-to-many class="News, NHibernateOneToMany" />
</set>
</class>
</hibernate-mapping>
导致多个查询的查询:
var news = newsRepository.Linq().Skip(DefaultPageSize*currentPageIndex).Take(DefaultPageSize).OrderByDescending(x => x.Date).ToList();
这就是没有冗余选择的方法:
var criteria = Session.CreateCriteria<News>();
criteria = criteria.AddOrder(Order.Desc(property));
criteria = criteria.SetMaxResults(pageSize).SetFirstResult((pageNumber - 1)*pageSize);
var news = criteria.List<News>();