实体框架 - 加入列表 [英] Entity Framework - Join to a List

问题描述

我需要从我的数据库中检索与纯列表（而不是EF）中的项目列表相匹配的实体列表。实体框架4.1可以实现吗？

I need to retrieve a list of entities from my database that matches a list of items in a plain list (not EF). Is this possible with Entity Framework 4.1?

示例：

var list = new List<string> { "abc", "def", "ghi" };
var items = from i in context.Items
            where list.Contains(i.Name)
            select i;

这可以很好地返回匹配一个属性的行，但实际上有一个更复杂的属性： / p>

This works great to return rows that match one property, but I actually have a more complex property:

var list = new List<Tuple<string, string>>
{
    new Tuple<string,string>("abc", "123"),
    new Tuple<string,string>("def", "456")
};

// i need to write a query something like this:
var items = from i in context.Items
where list.Contains(new Tuple<string,string>(i.Name, i.Type))
select i;

我知道这是无效的，因为它会说它需要是一个原始类型，但是在那里任何方式做我想要完成的任务，或者我需要诉诸一个存储过程？

I know that is not valid because it will say it needs to be a primitive type, but is there any way to do what I'm trying to accomplish or will I need to resort to a stored procedure?

推荐答案

你有一个几个选项：

1）当然可以编写一个存储过程来做你需要的，并调用它。

1) You could, of course, write a stored procedure to do what you need and call it.

2）您可以将表读入内存，然后在内存列表中查询...这样您就不必使用原语：

2) You could read the table into memory and then query the in memory list...that way you don't have to use primitives:

var items = from i in context.Items.ToList()
            where list.Contains(new Tuple<string, string>(i.Name, i.Type))
            select i;

3）您还可以将查询转换为使用原语来实现相同的目标：

3) You could also convert your query to use primitives to achieve the same goal:

var items = from i in context.Items
            join l in list
            on new { i.Name, i.Type } equals 
                new { Name = l.Item1, Type = l.Item2 }
            select i;

只要表不是非常大，请随意选择第二个选项。否则，先走。

I would go with the second option as long as the table isn't extremely large. Otherwise, go with the first.

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