分页模块

0. 参数传递（从URL到代码查询）：参考解析URL中的批量信息中最后的方法

public class PaginationResourceParamaters
    {
        private int _pageNumber = 1;
        public int PageNumber
        {
            get
            {
                return _pageNumber;
            }
            set
            {
                if (value >= 1)
                {
                    _pageNumber = value;
                }
            }
        }
        private int _pageSize = 10;
        const int maxPageSize = 50;
        public int PageSize
        {
            get
            {
                return _pageSize;
            }
            set
            {
                if (value >= 1)
                {
                    _pageSize = (value > maxPageSize) ? maxPageSize : value;
                }
            }
        }
    }

调用
private string GenerateTouristRouteResourceURL(TouristRouteResourceParamaters paramaters, PaginationResourceParamaters paramaters2,ResourceUriType type)

1. 功能实现

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace FakeXiecheng.API.Helper
{
    public class PaginationList<T> : List<T>
    {
        public int TotalPages { get; private set; }
        public int TotalCount { get; private set; }
        public bool HasPrevious => CurrentPage > 1;
        public bool HasNext => CurrentPage < TotalPages;

        public int CurrentPage { get; set; }
        public int PageSize { get; set; }

        public PaginationList(int totalCount, int currentPage, int pageSize, List<T> items)
        {
            CurrentPage = currentPage;
            PageSize = pageSize;
            AddRange(items);
            TotalCount = totalCount;
            TotalPages = (int)Math.Ceiling(totalCount / (double)pageSize);
        }

        public static async Task<PaginationList<T>> CreateAsync( int currentPage, int pageSize, IQueryable<T> result)
        {
            var totalCount = await result.CountAsync();
            // pagination
            // skip
            var skip = (currentPage - 1) * pageSize;
            result = result.Skip(skip);
            // 以pagesize为标准显示一定量的数据
            result = result.Take(pageSize);

            // include vs join
            var items = await result.ToListAsync();

            return new PaginationList<T>(totalCount, currentPage, pageSize, items);
        }
    }
}

2. 用法：在仓储模式创建查询对象的时候（参考IQueryable中有关创建查询对象和执行查询的描述）将IQueryable的查询对象和相关分页参数放进PaginationList.CreateAsync()方法中运行，并获取其结果（结果为已经执行了查询的结果，所以分页要放在查询的最后执行）
   var touristRoutesFromRepo = await _touristRouteRepository.GetTouristRoutesAsync(paramaters.Keyword, paramaters.RatingOperator, paramaters.RatingValue, paramaters2.PageSize, paramaters2.PageNumber, paramaters.OrderBy );

        public async Task<PaginationList<TouristRoute>> GetTouristRoutesAsync(string keyword, string ratingOperator, int? ratingValue, int pageSize, int pageNumber,string orderBy)
        {
            IQueryable<TouristRoute> result = _context.TouristRoutes.Include(t => t.TouristRoutePictures);
            return await PaginationList<TouristRoute>.CreateAsync(pageNumber, pageSize, result);
        }