如果不支持Contains,如何在LINQ to Entities(实体框架)中执行SQL样式的"IN"语句？

Question

我正在使用LINQ to Entities(而不是LINQ to SQL),而且我在创建'IN'样式查询时遇到了麻烦.这是我目前的询问:

var items = db.InventoryItem
                .Include("Kind")
                .Include("PropertyValues")
                .Include("PropertyValues.KindProperty")
                .Where(itm => valueIds.Contains(itm.ID)).ToList<InventoryItem>();

但是,当我这样做时,抛出以下异常:

LINQ to Entities无法识别方法'Boolean Contains(Int64)'方法,并且此方法无法转换为商店表达式.

有没有人有解决方法或其他解决方案？

Answer 1

你需要使用这个:

.Where(string.Format("it.ID in {0}", string.Join(",", valueIds.ToArray())));

或动态构造WHERE部分,如本文所述.

PS - 信息已更新,此答案更新如下,以保持相关性:

引用的链接包含以下更新:

...在EF4中,我们添加了对 Contains方法的 支持,至少在这个特定情况下是对集合值 参数的支持.因此,这种 代码现在可以直接使用, 并且不需要使用任何 附加表达式构建方法:

var statusesToFind = new List<int> {1, 2, 3, 4};
var foos = from foo in myEntities.Foos
           where statusesToFind.Contains(foo.Status)
           select foo;

Answer 2

Any在某些情况下,您可以使用Linq的扩展方法:

var userIds = new[] { 1, 2, 3 };

from u in Users
     where userIds.Any(i => i==u.Id)
     select u;

在这种情况下生成的SQL看起来很奇怪,但是像Linq-to-Entities生成的SQL一样,对于人来说它可能过于冗长,但在实践中运行速度很快.

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[DisplayName] AS [DisplayName], 
FROM [dbo].[Users] AS [Extent1]
WHERE  EXISTS (SELECT 
    1 AS [C1]
    FROM  (SELECT 
        [UnionAll1].[C1] AS [C1]
        FROM  (SELECT 
            1 AS [C1]
            FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
        UNION ALL
            SELECT 
            2 AS [C1]
            FROM  ( SELECT 1 AS X ) AS [SingleRowTable2]) AS [UnionAll1]
    UNION ALL
        SELECT 
        3 AS [C1]
        FROM  ( SELECT 1 AS X ) AS [SingleRowTable3]) AS [UnionAll2]
    WHERE [UnionAll2].[C1] = [Extent1].[Id]
)