[英]Linq to Entities, Inject Join Inside Query Expression
I'm trying to improve the performance for some of our LINQ queries and there is one little thing that has a lot of space for improvement: joins. 我正在尝试提高某些LINQ查询的性能,有一件小事情需要大量改进:联接。 Almost all my queries have some join that is used to filter the result, but are not selected into de result.
几乎我所有的查询都有一些用于过滤结果的联接,但未选择到结果中。 And these filtering conditions are optional...
这些过滤条件是可选的...
What I have today is something like: 我今天所拥有的是:
var q = from t1 in context.Set<T1>()
where t1.mandatoryfilter >= 0
select t1;
if (useFilter)
{
var q2 = from t1 in q
from t2 in context.Set<T2>().Where(t2 => t2.fk == t1.pk).DefaultIfEmpty
where t2.filterProperty == filterValue
select t1;
if (useFilter2)
{
[...]
return q3.ToList();
}
return q2.ToList();
}
else
{
if (useFilter2)
{
[...]
return q2.ToList();
}
return q.ToList();
}
This will generate a projection of the query. 这将生成查询的投影。 And depending on the complexity/quantity of the filters it will generate more and more projections and the code need to be nested if I need to combine some of the filters.
并且根据过滤器的复杂性/数量,它会生成越来越多的投影,并且如果我需要组合一些过滤器,则需要嵌套代码。 The resulting query can grow to a size where it gets too large to send over the internet (not actually too large XD but it becomes a performance issue) and the code itself gets hard to maintain.
结果查询的大小可能会变得很大,以致无法通过Internet发送(实际上不是太大的XD,但它会导致性能问题),并且代码本身也很难维护。
I know I could just change back to string SQL... but that is not a very elegant solution is it? 我知道我可以改回字符串SQL ...但这不是一个非常优雅的解决方案吗?
I'd like to know if there is a way to inject the join and the filter directly do the Expression Tree, so the provider would not generate the projections and the code would be linear and simple. 我想知道是否有一种方法可以注入联接,而过滤器直接执行表达式树,因此提供程序将不会生成投影,并且代码将是线性且简单的。
ps.: very important information, I'm using EF6, Linq-to-Entities, default SqlClient. ps:非常重要的信息,我使用的是EF6,Linq-to-Entities,默认SqlClient。
Thank you all in advance. 谢谢大家。
I'm not too confident with the query-syntax version of LINQ, and don't have VS open, so I'm using the method-syntax to make sure I get it correct: but the same idea applies. 我对LINQ的查询语法版本不太有把握,并且没有打开VS,因此我使用方法语法来确保我正确无误:但是同样的想法适用。
This is a fairly standard way of applying filters. 这是应用过滤器的相当标准的方法。 You don't create new queries each time, you simply append a predicate for each filter.
您不必每次都创建新查询,只需为每个过滤器附加一个谓词即可。 Works for joins too (and unless you're using a custom join you likely don't need to explicitly use
.Join
) 也适用于联接(除非您使用自定义联接,否则可能无需显式使用
.Join
)
var people = context.Set<Person>()
.Where(p => p.mandatoryFilter > 0);
if (filter.WithAddress != null)
people = people.Where(p => p.Address == filter.WithAddress);
if (filter.WithBossName != null)
people = people.Where(p => p.Boss.Name == filter.WithBossName);
return people.ToList();
If you use navigation properties you hardly ever need joins and you can apply most filter conditions as a single expression. 如果使用导航属性,则几乎不需要连接,并且可以将大多数过滤条件作为单个表达式应用。
Let's suppose your T1
entity has a navigation property T2
. 假设您的
T1
实体具有导航属性T2
。 The filter expression will look like this: 过滤器表达式将如下所示:
q = q.Where(q.T2.filterProperty1 == filterProperty == filterValue);
You also see here that you can just append an expression to the existing query q
. 您还可以在此处看到仅将表达式追加到现有查询
q
。
Now it turns into a commonly applied pattern to add filter conditions to an IQueryable
: 现在,它变成一种常用的模式,以向
IQueryable
添加过滤条件:
IQueryable<T1> query = from t1 in context.Set<T1>()
where t1.mandatoryfilter >= 0
select t1;
if (filterValue2 != null)
query = query.Where(t => t.T2.filterProperty == filterValue2);
if (filterValue3 != null)
query = query.Where(t => t.T3.filterProperty == filterValue3);
if (filterValue4 != null)
query = query.Where(t => t.T4.filterProperty == filterValue4);
(Note that query
should be cast to IQueryable
, otherwise the assignments query = query....
don't compile.) (请注意,
query
应IQueryable
为IQueryable
,否则分配query = query....
请勿编译。)
And now you can even apply filters to 1:n associations 现在,您甚至可以将过滤器应用于1:n关联
if (filterValue5 != null)
query = query.Where(t => t.T5s.Any(t5 => t5.filterProperty == filterValue5));
You can't do this if you use join
for filtering, because it would multiply the result set. 如果使用
join
进行过滤,则无法执行此操作,因为它将使结果集相乘。
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