结合表达式而不是在实体框架中使用多个查询 [英] Combine expressions instead of using multiple queries in entity framework
问题描述
i have following generic queryable (which may already have selections applied):
我尝试过：
IQueryable< tentity> queryable = DBSet< tentity> .AsQueryable（）;
然后有一个Provider类看起来像这样：
公共类提供商< tentity>
{
public Expression< func>< tentity，>>条件{得到;组; }
[...]
}
条件可以按以下方式定义每个实例：
条件=实体=> entity.Id == 3;
现在我想选择所有具有至少由DBSet的一个实体满足的条件的Provider实例：
List< provider> providers = [...];
var matchingProviders = providers.Where（provider => queryable.Any（provider.Condition））
这个问题：我开始查询列表中的每个Provider实例。我宁愿使用单个查询来获得相同的结果。
由于性能有问题，这个主题特别重要。如何使用单个
查询获得相同的结果并使用Linq语句或表达式树提高性能？
What I have tried:
IQueryable<tentity> queryable = DBSet<tentity>.AsQueryable();
Then there is the Provider class that looks like this:
public class Provider<tentity>
{
public Expression<func><tentity,>> Condition { get; set; }
[...]
}
The Condition could be defined per instance in the following fashion:
Condition = entity => entity.Id == 3;
Now I want to select all Provider instances which have a Condition that is met at least by one entity of the DBSet:
List<provider> providers = [...];
var matchingProviders = providers.Where(provider => queryable.Any(provider.Condition))
The problem with this: I'm starting a query for each Provider instance in the list. I'd rather use a single query to achieve the same result.
This topic is especially important because of questionable performance. How can I achieve the same results with a single
query and improve performance using Linq statements or Expression Trees?
推荐答案
好吧，如果你想要使用动态查询，请阅读：
如何：使用表达式用于构建动态查询的树（C＃和Visual Basic） [ ^ ]
带有表达式树的动态LINQ查询 - 简单对话 [ ^ ]
ScottGu&＃博客 - 动态LINQ（第1部分：使用L INQ动态查询库） [ ^ ]
Well, if you would like to use dynamic queries, please read this:
How to: Use Expression Trees to Build Dynamic Queries (C# and Visual Basic)[^]
Dynamic LINQ Queries with Expression Trees - Simple Talk[^]
ScottGu's Blog - Dynamic LINQ (Part 1: Using the LINQ Dynamic Query Library)[^]
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