使用PredicateExtensions创建sqlscriptes的一个问题

Question

这是我的逻辑代码：

var predicate = PredicateExtensions.False<Customer>();
predicate = predicate.Or(p => p.CustomerID.Contains("N"));

using (Entities e = new Entities())
{
    var r = from p in e.Customer.AsQueryable().Where(predicate.Compile())
            select p;
    foreach (var _r in r)
        Console.WriteLine(_r.CustomerID);
}

然后我使用sql server profiler获取这样的sql脚本：

SELECT 
[Extent1].[CustomerID] AS [CustomerID], 
[Extent1].[Custname] AS [CustEname], 
[Extent1].[Site] AS [DefaultSite], 
[Extent1].[Currency] AS [Currency], 
[Extent1].[PayTerm] AS [PayTerm], 
[Extent1].[BAddr1] AS [BillAddr1], 
[Extent1].[BAddr2] AS [BillAddr2], 
[Extent1].[BAddr3] AS [BillAddr3], 
[Extent1].[BContact] AS [BillContact], 
[Extent1].[BTel] AS [BillTel], 
[Extent1].[BFax] AS [BillFax], 
[Extent1].[BEMail] AS [BillEMail], 
[Extent1].[Company] AS [DlvyCompany], 
[Extent1].[Addr1] AS [DlvyAddr1], 
[Extent1].[Addr2] AS [DlvyAddr2], 
[Extent1].[Addr3] AS [DlvyAddr3], 
[Extent1].[Contact] AS [DlvyContact], 
[Extent1].[Tel] AS [DlvyTel], 
[Extent1].[Fax] AS [DlvyFax], 
[Extent1].[EMail] AS [DlvyEMail], 
[Extent1].[Remark] AS [Remark], 
[Extent1].[User] AS [User], 
[Extent1].[DT] AS [UpdateDT]
FROM [dbo].[Customer] AS [Extent1]

我从数据库中获取所有数据，但我希望sql脚本末尾有一个条件，意味着获取所有数据但customeid包含N(p => p.CustomerID.Contains("N"))

，我得到了一些错误...... 请给一些积分。谢谢！

Answer 1

问题出在 Compile() 方法上。您想要使用的 IQueryable 扩展方法需要表达式作为其参数。在您的情况下，调用 AsQueryable() 不会执行任何操作，并且 IEnumerable 扩展方法 Where(Func)被叫。您想要做的是调用 IQueryable 扩展方法 Where(Expression>) 来代替。要做到这一点很简单：只需不要调用 Compile()，predicate 已经是一个表达式。另外，您使用查询表达式 (from ...) 的方式（几乎）不会执行任何操作，因此您可以将其省略：

var r = e.Customer.Where(predicate);