本文章是从大牛那边摘录过来，欢迎大家参考其区别和用途。欢迎指正。
IEnumerable接口
公开枚举器，该枚举器支持在指定类型的集合上进行简单迭代。也就是说：实现了此接口的object，就可以直接使用foreach遍历此object；
IQueryable 接口
它继承 IEnumerable 接口，而因为.net版本加入Linq和IQueryable后，使得IEnumerable不再那么单调，变得更加强大和丰富。
为了区别两个接口，我们通过一个实际的例子来解释一下。
#region 用户管理列表
///
/// 用户管理列表
///
///
public ActionResult List()
{
//IQueryable
IQueryable
orderby u.id
select u).Skip
//IEnumerable
IEnumerable
orderby u.id
select u).AsEnumerable
int i = 0;
foreach (var c in userlistIQue)
{
i++;
}
Console.WriteLine(i);
foreach (var c in userlistIEnu)
{
i++;
}
Console.WriteLine(i);
return View();
}
#endregion
IQueryable的，会先帮你执行Skip
IEnumerable ,则是查询出所有的数据，放到内存中来。
.AsEnumerable() 和 .AsQueryable()
string strcon = "Data Source=.\\SQLEXPRESS;Initial Catalog=Db_Example;Persist Security Info=True;User ID=sa;Password=sa";
SqlConnection con = new SqlConnection(strcon);
con.Open();
string strsql = "select * from SC,Course where SC.Cno=Course.Cno";
SqlDataAdapter da = new SqlDataAdapter(strsql,con);
DataSet ds = new DataSet();
da.Fill(ds, "mytable");
DataTable tables=ds.Tables["mytable"]; //创建表
var dslp = from d in tables.AsEnumerable() select d;//执行LINQ语句,这里的.AsEnumerable()是延迟发生,不会立即执行，实际上什么都没有发生
foreach(var res in dslp)
{
Response.Write(res.Field
}
1、AsEnumerable()是延迟执行的，实际上什么都没有发生，当真正使用对象的时候（例如调用：First, Single, ToList....的时候）才执行。
2、AsEnumerable将一个序列向上转换为一个IEnumerable, 强制将Enumerable类下面的查询操作符绑定到后续的子查询当中。
3、AsQueryable将一个序列向下转换为一个IQueryable, 它生成了一个本地查询的IQueryable包装。
4、AsEnumerable()延迟执行，不会立即执行。当你调用.AsEnumerable()的时候，实际上什么都没有发生。
5、ToList()立即执行
6、当你需要操作结果的时候，用.ToList()，否则，如果仅仅是用来查询不需要进一步使用结果集，并可以延迟执行，就用.AsEnumerable()/IEnumerable /IQueryable
7、AsEnumerable()虽然延迟执行，但还是访问数据库，而.ToList()直接取得结果放在内存中。比如我们需要显示两个部门的员工时，部门可以先取出放置在List中，然后再依次取出各个部门的员工，这时访问的效率要高一些，因为不需要每次都访问数据库去取出部门。
8、IQueryable实现了IEnumberable接口。但IEnumerable
9、IQueryable接口与IEnumberable接口的区别： IEnumerable
10、IEnumerable跑的是Linq to Object，强制从数据库中读取所有数据到内存先。
二、AsEnumerable和AsQueryable的实例
using (testContext context = new testContext())
...{ var query = (from item in context.Users.AsQueryable() where item.id > 10 select item.id).ToList(); var query2 = (from item in context.Users.AsEnumerable() where item.id > 10 select item.id).ToList(); }
服务器端sql
--AsQueryable Select
[Extent1].[id] AS [id]
FROM [dbo].[User] AS [Extent1]
Where [Extent1].[id] > 10
--AsEnumerable Select
[Extent1].[id] AS [id],
[Extent1].[usn] AS [usn],
[Extent1].[pwd] AS [pwd],
[Extent1].[created] AS [created]
FROM [dbo].[User] AS [Extent1]
using (testContext context = new testContext())
...{ var query = (from item in context.Users.AsQueryable() where item.id > 10 orderby item.id ascending select item.id).Skip(20).Take(20).ToList(); var query2 = (from item in context.Users.AsEnumerable() where item.id > 10 orderby item.id ascending select item.id).Skip(20).Take(20).ToList(); }
服务器端sql
--AsQueryable Select TOP (20)
[Filter1].[id] AS [id]
FROM ( Select [Extent1].[id] AS [id], row_number() OVER (ORDER BY [Extent1].[id] ASC) AS [row_number]
FROM [dbo].[User] AS [Extent1]
Where [Extent1].[id] > 10
) AS [Filter1]
Where [Filter1].[row_number] > 20
orDER BY [Filter1].[id] ASC
--AsEnumerable Select
[Extent1].[id] AS [id],
[Extent1].[usn] AS [usn],
[Extent1].[pwd] AS [pwd],
[Extent1].[created] AS [created]
FROM [dbo].[User] AS [Extent1]
二、AsEnumerable和AsQueryable的实例
using (testContext context = new testContext())
...{ var query = (from item in context.Users.AsQueryable() where item.id > 10 select item.id).ToList(); var query2 = (from item in context.Users.AsEnumerable() where item.id > 10 select item.id).ToList(); }
服务器端sql
--AsQueryable Select
[Extent1].[id] AS [id]
FROM [dbo].[User] AS [Extent1]
Where [Extent1].[id] > 10
--AsEnumerable Select
[Extent1].[id] AS [id],
[Extent1].[usn] AS [usn],
[Extent1].[pwd] AS [pwd],
[Extent1].[created] AS [created]
FROM [dbo].[User] AS [Extent1]
using (testContext context = new testContext())
...{ var query = (from item in context.Users.AsQueryable() where item.id > 10 orderby item.id ascending select item.id).Skip(20).Take(20).ToList(); var query2 = (from item in context.Users.AsEnumerable() where item.id > 10 orderby item.id ascending select item.id).Skip(20).Take(20).ToList(); }
服务器端sql
--AsQueryable Select TOP (20)
[Filter1].[id] AS [id]
FROM ( Select [Extent1].[id] AS [id], row_number() OVER (ORDER BY [Extent1].[id] ASC) AS [row_number]
FROM [dbo].[User] AS [Extent1]
Where [Extent1].[id] > 10
) AS [Filter1]
Where [Filter1].[row_number] > 20
orDER BY [Filter1].[id] ASC
--AsEnumerable Select
[Extent1].[id] AS [id],
[Extent1].[usn] AS [usn],
[Extent1].[pwd] AS [pwd],
[Extent1].[created] AS [created]
FROM [dbo].[User] AS [Extent1]