c# - Entity Framework 4.0 : Method cannot be translated into a store expression

Question

我有这段代码，其中 Customers 是 IQueryable<Customer>

Customers = Customers.Where ( C => Int32.Parse(C.Salary) > 5000);

当我运行时出现错误 Method cannot be translated into a store expression .现在我知道我需要为此使用 EntityFunctions(即 EF 的规范函数)，但是当我检查 EntityFunctions 中的列表时，没有可用于将字符串转换为整数的方法。

注意:我知道如果我对对象执行 Linq，即在 IQueryable 上执行 ToList()，然后进行过滤，一切都可以。但我不想这样做，因为这会降低我的性能，因为 Customers 表的行数太大。也无法将我的数据库字段转换为 int。

更新:我正在使用 Sql Server 2008。如果它有任何帮助，我会考虑包含它。

更新 2: Aducci 在他的回答中提供了一个真正巧妙而巧妙的解决方案。但是从中生成的Sql非常难看。例如:

SELECT 
[GroupBy1].[A1] AS [C1]
FROM ( SELECT 
    COUNT(1) AS [A1]
    FROM ( SELECT 
        [Project2].[C1] AS [C1], 
        (SELECT TOP (1) [top].[C1] AS [C1]
            FROM ( SELECT TOP (1) 
                 CAST( [Project2].[PostalCode] AS int) AS [C1]
                FROM [dbo].[Customers] AS [c]
            )  AS [top]) AS [C2]
        FROM ( SELECT 
            [Extent1].[PostalCode] AS [PostalCode], 
            (SELECT TOP (1) [top].[C1] AS [C1]
                FROM ( SELECT TOP (1) 
                     CAST( [Extent1].[PostalCode] AS int) AS [C1]
                    FROM [dbo].[Customers] AS [c]
                )  AS [top]) AS [C1]
            FROM [dbo].[Customers] AS [Extent1]
        )  AS [Project2]
    )  AS [Project4]
    WHERE (CASE WHEN ([Project4].[C1] IS NULL) THEN 0 ELSE [Project4].[C2] END) > 5000
)  AS [GroupBy1]

唯一的区别是它使用邮政编码而不是薪水。如果您不是真的很担心这个丑陋的 Sql，您当然可以使用，但如果您是，那么我在我的评论中提供了 1 个链接，它以非常好的和高效的方式工作。

这是我提到的链接生成的等效 Sql:

SELECT 
[GroupBy1].[A1] AS [C1]
FROM ( SELECT 
    COUNT(1) AS [A1]
    FROM [dbo].[Customers] AS [Extent1]
    WHERE  CAST(  CAST( [Extent1].[PostalCode] AS int) AS float) > cast(5000 as float(53))
)  AS [GroupBy1]

Answer 1

如果所有字符串值都是有效整数，这将起作用

var query = from c in Customers
            let salaryInt = Customers.Take(1).Select(x => c.Salary).Cast<int>().FirstOrDefault()
            where salaryInt > 5000
            select c;