过滤，合并，排序和页面数据从多个来源

我认为你可以使用以下算法。假设页面大小为10，那么对于第0页:

1. 从数据库A中获得10个结果，在db级别进行过滤和排序。
2. 从数据库B中获得10个结果，在db级别进行过滤和排序(与上述查询并行)
3. 将这两个结果组合起来，以正确的排序顺序获得10条记录。所以你有20条记录排序，但只取前10条并显示在UI

第1页:

1. 请注意，在上一步中，您使用了多少项从数据库A和B中显示在UI中。例如，您使用了数据库A中的2项和数据库b中的8项。
2. 从数据库A获得10个结果，经过过滤和排序，但从位置2开始(跳过2)，因为这两个你已经在UI中显示了。
3. 从数据库B中获得10个结果，经过过滤和排序，但从位置8开始(跳过8)。
4. 与上面相同的方式合并，从20条记录中获得10条。假设现在您使用了来自A的5件物品和来自b的5件物品。现在，您总共显示了来自A的7件物品和来自b的13件物品。使用这些数字作为下一步。

这将不允许(容易地)跳过页面，但据我所知，这不是一个要求。

性能应该与查询单个数据库时的性能相同，因为对A和B的查询可以并行进行。

我在这里创建了一些东西，如果需要，我会回来解释。我不确定我的算法是否适用于所有的边缘情况，它涵盖了我想要的所有情况，但你永远不知道。我将把代码留在这里供您欣赏，我会回答并解释那里所做的事情，如果您需要，请留下评论。

并对值之间存在较大差距的项目列表执行多次测试。

using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApplication1
{
    class Program
    {
        //each time when this objects are accessed, consider as a database call
        private static IQueryable<model1> dbsetModel_1; 
        private static IQueryable<model2> dbsetModel_2;
        private static void InitDBSets()
        {
            var rnd = new Random();
            List<model1> dbsetModel1 = new List<model1>();
            List<model2> dbsetModel2 = new List<model2>();
            for (int i = 1; i < 300; i++)
            {
                if (i % 2 == 0)
                {
                    dbsetModel1.Add(new model1() { Id = i, OrderNumber = rnd.Next(1, 10), Name = "Test " + i.ToString() });
                }
                else
                {
                    dbsetModel2.Add(new model2() { Id2 = i, OrderNumber2 = rnd.Next(1, 10), Name2 = "Test " + i.ToString() });
                }
            }
            dbsetModel_1 = dbsetModel1.AsQueryable();
            dbsetModel_2 = dbsetModel2.AsQueryable();
        }
        public static void Main()
        {
            //generate sort of db data
            InitDBSets();
            //test
            var result2 = GetPage(new PagingFilter() { Page = 5, Limit = 10 });
            var result3 = GetPage(new PagingFilter() { Page = 6, Limit = 10 });
            var result5 = GetPage(new PagingFilter() { Page = 7, Limit = 10 });
            var result6 = GetPage(new PagingFilter() { Page = 8, Limit = 10 });
            var result7 = GetPage(new PagingFilter() { Page = 4, Limit = 20 });
            var result8 = GetPage(new PagingFilter() { Page = 200, Limit = 10 });
        }

        private static PagedList<Item> GetPage(PagingFilter filter)
        {
            int pos = 0;
            //load only start pages intervals margins from both database
            //this part need to be transformed in a stored procedure on db one, skip, take to return interval start value for each frame 
            var framesBordersModel1 = new List<Item>();
            dbsetModel_1.OrderBy(x => x.Id).ThenBy(z => z.OrderNumber).ToList().ForEach(i => {
                pos++;
                if (pos - 1 == 0)
                {
                    framesBordersModel1.Add(new Item() { criteria1 = i.Id, criteria2 = i.OrderNumber, model = i });
                }
                else if ((pos - 1) % filter.Limit == 0)
                {
                    framesBordersModel1.Add(new Item() { criteria1 = i.Id, criteria2 = i.OrderNumber, model = i });
                }
            });
            pos = 0;
            //this part need to be transformed in a stored procedure on db two, skip, take to return interval start value for each frame
            var framesBordersModel2 = new List<Item>();
            dbsetModel_2.OrderBy(x => x.Id2).ThenBy(z => z.OrderNumber2).ToList().ForEach(i => {
                pos++;
                if (pos - 1 == 0)
                {
                    framesBordersModel2.Add(new Item() { criteria1 = i.Id2, criteria2 = i.OrderNumber2, model = i });
                }
                else if ((pos -1) % filter.Limit == 0)
                {
                    framesBordersModel2.Add(new Item() { criteria1 = i.Id2, criteria2 = i.OrderNumber2, model = i });
                }
            });
            //decide where is the position of your cursor based on start margins
            //int mainCursor = 0;
            int cursor1 = 0;
            int cursor2 = 0;
            //filter pages start from 1, filter.Page cannot be 0, if indeed you have page 0 change a lil' bit he logic 
            if (framesBordersModel1.Count + framesBordersModel2.Count < filter.Page) throw new Exception("Out of range");
            while ( cursor1 + cursor2 < filter.Page -1)
            {
                if (framesBordersModel1[cursor1].criteria1 < framesBordersModel2[cursor2].criteria1)
                {
                    cursor1++;
                }
                else if (framesBordersModel1[cursor1].criteria1 > framesBordersModel2[cursor2].criteria1)
                {
                    cursor2++;
                }
                //you should't get here case main key sound't be duplicate, annyhow
                else
                {
                    if (framesBordersModel1[cursor1].criteria2 < framesBordersModel2[cursor2].criteria2)
                    {
                        cursor1++;
                    }
                    else
                    {
                        cursor2++;
                    }
                }
                //mainCursor++;
            }
            //magic starts
            //inpar skipable
            int skipEndResult = 0;
            List<Item> dbFramesMerged = new List<Item>();
            if ((cursor1 + cursor2) %2 == 0)
            {
                dbFramesMerged.AddRange(
                    dbsetModel_1.OrderBy(x => x.Id)
                        .ThenBy(z => z.OrderNumber)
                        .Skip(cursor1*filter.Limit)
                        .Take(filter.Limit)
                        .Select(x => new Item() {criteria1 = x.Id, criteria2 = x.OrderNumber, model = x})
                        .ToList()); //consider as db call EF or Stored Procedure
                dbFramesMerged.AddRange(
                    dbsetModel_2.OrderBy(x => x.Id2)
                        .ThenBy(z => z.OrderNumber2)
                        .Skip(cursor2*filter.Limit)
                        .Take(filter.Limit)
                        .Select(x => new Item() {criteria1 = x.Id2, criteria2 = x.OrderNumber2, model = x})
                        .ToList());
                ; //consider as db call EF or Stored Procedure
            }
            else
            {
                skipEndResult = filter.Limit;
                if (cursor1 > cursor2)
                {
                    cursor1--;
                }
                else
                {
                    cursor2--;
                }
                dbFramesMerged.AddRange(
                   dbsetModel_1.OrderBy(x => x.Id)
                       .ThenBy(z => z.OrderNumber)
                       .Skip(cursor1 * filter.Limit)
                       .Take(filter.Limit)
                       .Select(x => new Item() { criteria1 = x.Id, criteria2 = x.OrderNumber, model = x })
                       .ToList()); //consider as db call EF or Stored Procedure
                dbFramesMerged.AddRange(
                    dbsetModel_2.OrderBy(x => x.Id2)
                        .ThenBy(z => z.OrderNumber2)
                        .Skip(cursor2 * filter.Limit)
                        .Take(filter.Limit)
                        .Select(x => new Item() { criteria1 = x.Id2, criteria2 = x.OrderNumber2, model = x })
                        .ToList());
            }
            IQueryable<Item> qItems = dbFramesMerged.AsQueryable();
            PagedList<Item> result = new PagedList<Item>();
            result.AddRange(qItems.OrderBy(x => x.criteria1).ThenBy(z => z.criteria2).Skip(skipEndResult).Take(filter.Limit).ToList());
            //here again you need db cals to get total count
            result.Total = dbsetModel_1.Count() + dbsetModel_2.Count();
            result.Limit = filter.Limit;
            result.Page = filter.Page;
            return result;
        }
    }
    public class PagingFilter
    {
        public int Limit { get; set; }
        public int Page { get; set; }
    }

    public class PagedList<T> : List<T>
    {
        public int Total { get; set; }
        public int? Page { get; set; }
        public int? Limit { get; set; }
    }
    public class Item : Criteria
    {
        public object model { get; set; }
    }
    public class Criteria
    {
        public int criteria1 { get; set; }
        public int criteria2 { get; set; }
        //more criterias if you need to order
    }
    public class model1
    {
        public int Id { get; set; }
        public int OrderNumber { get; set; }
        public string Name { get; set; }
    }
    public class model2
    {
        public int Id2 { get; set; }
        public int OrderNumber2 { get; set; }
        public string Name2 { get; set; }
    }
}