只是好奇 Skip & Take 应该如何工作。我得到了我想在客户端看到的结果,但是当我连接 AnjLab SQL Profiler 并查看正在执行的 SQL 时,它看起来好像正在查询并将整组行返回到客户。
它真的会返回所有行,然后在客户端使用 LINQ 进行排序和缩小范围吗?
我尝试过使用 Entity Framework 和 Linq to SQL 来实现;两者似乎具有相同的行为。
不确定它有什么不同,但我在 VWD 2010 中使用 C#。
有什么见解吗?
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();
}
生成的 SQL(注意:我排除了 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]
经过进一步的研究,我发现下面的方法符合我的预期:
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);
}
生成的 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
我真的很喜欢第一个选项的工作方式;传入 lambda 表达式进行排序。有什么方法可以在 LINQ to SQL orderby 语法中完成同样的事情吗?我尝试使用 qry.OrderBy(sort).Skip(skipRows).Take(pageSize),但最终得到的结果与我的第一段代码相同。让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 函数包装在表达式中:
Expression<Func<Store,string>> sort
最佳答案
以下工作并实现了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;
}
为我修复它的主要事情是将 Func 排序参数更改为:
Expression<Func<Store, string>> sort
关于c# - Entity Framework /Linq to SQL : Skip & Take,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3870091/