如何在不检索所有行的情况下使用 Entity Framework Core 3.0 实现分组分页?

How to implement pagination with group by using Entity Framework Core 3.0 without retrieving all rows?

当输入数据需要先分组时,你会如何实现分页?我从下面的 link 了解如何实现分页:

LINQ and pagination

,但我希望能够做到这一点,其中分页列表中的每个项目都是来自输入数据的一个组(可以扩展)。类似于下面的代码——为了防止将 table 的所有行检索到内存中,ordersList 是 IQueryable。返回的 IQueryable 是我想传递给分页函数的内容。

from order in ordersList
group order by order.FullName into customers
select customers

然而,这样的查询在客户端上运行(实际上在 Entity Framework Core 3.0+ 中抛出异常)。对于这种情况,有没有办法只检索当前页面上的项目?

您必须按组分页。您应该使用 group number 而不是 page number

//group sequence
int groupSeq = 1;

//select current group
var p = (from order in context.TBLGroups
       group order by order.FullName into customers
       select customers.Key).OrderBy(a => a).Skip(groupSeq - 1).Take(1).FirstOrDefault();
       string FullName = p.ToString();

//get all items in current group
var items = (from order in context.TBLGroups
       where order.FullName == FullName
       select order).ToList();

您必须检索有限的数据,然后在客户端分组:

var keys = ordersList
   .Select(o => new {o.FullName})
   .Distinct()
   .OrderBy(о => o.FullName)
   .Skip(pageNumber * pageSize)
   .Take(pageSize);

var items =
   from order in ordersList
   join key in keys on order.FullName equals key.FullName
   select order;

var result = 
   from order in items.AsEnumerable()
   group order by order.FullName into customers
   select customers;