[英]What is the best way to test a condition in Linq to NHibernate?
Any()linq函数似乎加载了实体的所有列,即使它们并不需要。
如下代码:
if(Session.Query<Project>().Any(p=>p.ID == projectID && p.ProjectOwner.Responsible == CurrentUserID))
// Current user is the responsible for this project
生成以下SQL:
select TOP (1) project0_.ProjectID as ProjectID7_,
project0_.DateCreated as DateCrea2_7_,
project0_.Type as Type7_,
project0_.ProjectOwner_FK as ProjectOy8_7_,
project0_.Address_FK as Address9_7_,
**[Snip -- the statement selects all of Project's columns]**
from [Project] project0_
inner join [OrganizationProject] organizati1_
on project0_.ProjectOwner_FK = organizati1_.OrganizationProjectID
where project0_.ProjectID = 1 /* @p0 */
and organizati1_.Responsible_FK = 1 /* @p1 */
但是,以下代码:
if(Context.Projects.Where(p=>p.ID == projectID && p.ProjectOwner.Responsible == CurrentUserID).Count() == 1)
// Current user is the responsible for this project
生成以下sql,这是预期的结果:
select cast(count(*) as INT) as col_0_0_
from [Project] project0_
inner join [OrganizationProject] organizati1_
on project0_.ProjectOwner_FK = organizati1_.OrganizationProjectID
where project0_.ProjectID = 1 /* @p0 */
and organizati1_.Responsible_FK = 1 /* @p1 */
Count()方法可以完成预期的工作,但不太直接。
是Any()行为被认为是正常的还是错误? 这对我来说似乎不是最佳选择,但是也许加载实体并不比要求SQL返回计数慢吗?
有鉴于此, 什么是在Linq to NHibernate中测试条件的最佳方法?
这很有趣,但是您是否尝试过:
if(Session.Query<Project>()
.FirstOrDefault(p=>p.ID == projectID
&& p.ProjectOwner.Responsible == CurrentUserID) != null)
我认为从您当前的选择中可以更快。 实际上,它不会检查所有项(例如count),也不会获取所有数据。
这样的事情应该创建一个仅包含一列的查询:
if(Session
.Query<Project>()
.Where(p=>p.ID == projectID && p.ProjectOwner.Responsible == CurrentUserID)
.Select(p=>new { pID = p.ID })
.Any())
{
...
}
投影到匿名类型允许NHibernate仅获取指定的列(例如ID)。
但是,当要检索的行数量很多时,它通常更适合。
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