Question

在NHibernate中，当我们执行下面的查询时，为它生成的SQL将包含集合中每个元素的参数。如果对MSSQL Server执行查询，并且集合中有2k或更多元素，则会出现错误，因为sql引擎允许的最大参数为2k。

var bankaccounts = from b in this.unitOfWork.BankAccounts
                    where command.Ids.Contains(b.Id) // command.ids is an array with id's
                    select b;

很抱歉懒得用EntityFramework自己测试一下，但我看到其他开发人员编写这样的代码：EF cannot delete child object because of associationset

问题是EF将为这类查询生成哪些SQL？

Answer 1

我已经为你看了SQL分析器。这就是实体框架中发生的事情（我认为这是wat NHibernate也会产品，但我不确定..）：

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[AccountNo] AS [AccountNo], 
[Extent1].[Name] AS [Name], 
[Extent1].[Description] AS [Description], 
[Extent1].[IBAN] AS [IBAN], 
[Extent1].[IsActive] AS [IsActive], 
[Extent1].[Customer_Id] AS [Customer_Id]
FROM [dbo].[BankAccounts] AS [Extent1]
WHERE [Extent1].[Id] IN (4,5,6,7,9)

如您所见，它将变为WHERE .. IN ([the contains values])

Answer 2

使用此查询，

    var ids = context.Countries
        .Take(10).Select(c => c.CountryId).ToList();

    var offices = context.Offices.Where(o => ids.Contains(o.CountryId))
        .ToList();

它将生成此SQL：

SELECT 
[Extent1].[OfficeId] AS [OfficeId], 
[Extent1].[CountryId] AS [CountryId],
[Extent1].[OfficeName] AS [OfficeName]
FROM [dbo].[Office] AS [Extent1]
WHERE [Extent1].[CountryId] IN (3,4,5,6,7,8,9,10,11,12)

EF：在LINQ查询中使用Contains时SQL输出是什么？

2 个答案: