小编典典

实体框架/ Linq to SQL：跳过并接受

只是对“跳过和获取”应该如何工作感到好奇。我正在获得要在客户端看到的结果，但是当我挂接AnjLab SQL
Profiler并查看正在执行的SQL时，它看起来好像是在查询并将整个行集返回给客户。

它真的返回所有行，然后在客户端使用LINQ排序并缩小范围吗？

我曾经尝试使用Entity Framework和Linq to SQL来完成；两者似乎具有相同的行为。

不确定是否有任何区别，但是我在VWD 2010中使用C＃。

有见识吗？

public IEnumerable<Store> ListStores(Func<Store, string> sort, bool desc, int page, int pageSize, out int totalRecords)
{
    var context = new TectonicEntities();
    totalRecords = context.Stores.Count();
    int skipRows = (page - 1) * pageSize;
    if (desc)
        return context.Stores.OrderByDescending(sort).Skip(skipRows).Take(pageSize).ToList();
    return context.Stores.OrderBy(sort).Skip(skipRows).Take(pageSize).ToList();
}

产生的SQL（注意：我不包括Count查询）：

SELECT 
[Extent1].[ID] AS [ID], 
[Extent1].[Name] AS [Name], 
[Extent1].[LegalName] AS [LegalName], 
[Extent1].[YearEstablished] AS [YearEstablished], 
[Extent1].[DiskPath] AS [DiskPath], 
[Extent1].[URL] AS [URL], 
[Extent1].[SecureURL] AS [SecureURL], 
[Extent1].[UseSSL] AS [UseSSL]
FROM [dbo].[tec_Stores] AS [Extent1]

经过一些进一步的研究，我发现以下方法可以达到我期望的方式：

public IEnumerable<Store> ListStores(Func<Store, string> sort, bool desc, int page, int pageSize, out int totalRecords)
{
    var context = new TectonicEntities();
    totalRecords = context.Stores.Count();
    int skipRows = (page - 1) * pageSize;           
    var qry = from s in context.Stores orderby s.Name ascending select s;
    return qry.Skip(skipRows).Take(pageSize);           
}

产生的SQL：

SELECT TOP (3) 
[Extent1].[ID] AS [ID], 
[Extent1].[Name] AS [Name], 
[Extent1].[LegalName] AS [LegalName], 
[Extent1].[YearEstablished] AS [YearEstablished], 
[Extent1].[DiskPath] AS [DiskPath], 
[Extent1].[URL] AS [URL], 
[Extent1].[SecureURL] AS [SecureURL], 
[Extent1].[UseSSL] AS [UseSSL]
FROM ( SELECT [Extent1].[ID] AS [ID], [Extent1].[Name] AS [Name], [Extent1].[LegalName] AS [LegalName], [Extent1].[YearEstablished] AS [YearEstablished], [Extent1].[DiskPath] AS [DiskPath], [Extent1].[URL] AS [URL], [Extent1].[SecureURL] AS [SecureURL], [Extent1].[UseSSL] AS [UseSSL], row_number() OVER (ORDER BY [Extent1].[Name] ASC) AS [row_number]
    FROM [dbo].[tec_Stores] AS [Extent1]
)  AS [Extent1]
WHERE [Extent1].[row_number] > 3
ORDER BY [Extent1].[Name] ASC

我真的很喜欢第一种方法的工作方式。传递lambda表达式进行排序。有什么方法可以在LINQ to SQL
orderby语法中完成相同的工作吗？我尝试使用qry.OrderBy（sort）.Skip（skipRows）.Take（pageSize），但这最终给了我与第一段代码相同的结果。使我相信我的问题在某种程度上与OrderBy有关。

===================================

问题解决了

必须将传入的lambda函数包装在Expression中：

Expression<Func<Store,string>> sort

阅读 258

2020-05-19

共1个答案

小编典典

以下工作可以实现我一直在寻找的简单性：

public IEnumerable<Store> ListStores(Expression<Func<Store, string>> sort, bool desc, int page, int pageSize, out int totalRecords)
{
    List<Store> stores = new List<Store>();
    using (var context = new TectonicEntities())
    {
        totalRecords = context.Stores.Count();
        int skipRows = (page - 1) * pageSize;
        if (desc)
            stores = context.Stores.OrderByDescending(sort).Skip(skipRows).Take(pageSize).ToList();
        else
            stores = context.Stores.OrderBy(sort).Skip(skipRows).Take(pageSize).ToList();
    }
    return stores;
}

为我修复的主要问题是将Func排序参数更改为：

Expression<Func<Store, string>> sort

2020-05-19