Asp.net Core 源码-PagedList<T>

我就是我 2021-11-15 12:56 221阅读 0赞

using System.Collections.Generic;
    using System.Linq;
    using System;
    using System.Linq.Expressions;
    using System.Diagnostics;
    
    namespace SportsStore.Models.Pages {
    
        public class PagedList<T> : List<T> {
    
            public PagedList(IQueryable<T> query, QueryOptions options = null) {
                CurrentPage = options.CurrentPage;
                PageSize = options.PageSize;
                Options = options;
    
                if (options != null) {
                    if (!string.IsNullOrEmpty(options.OrderPropertyName)) {
                        query = Order(query, options.OrderPropertyName, 
                            options.DescendingOrder);
                    }
                    if (!string.IsNullOrEmpty(options.SearchPropertyName) 
                            && !string.IsNullOrEmpty(options.SearchTerm)) {
                        query = Search(query, options.SearchPropertyName, 
                            options.SearchTerm);
                    }
                }
    
                //Stopwatch sw = Stopwatch.StartNew();
                //Console.Clear();
    
                TotalPages = query.Count() / PageSize;
                AddRange(query.Skip((CurrentPage - 1) * PageSize).Take(PageSize));
    
                //Console.WriteLine($"Query Time: {sw.ElapsedMilliseconds} ms");
            }
    
            public int CurrentPage { get; set; }
            public int PageSize { get; set; }
            public int TotalPages { get; set; }
            public QueryOptions Options { get; set; }
    
            public bool HasPreviousPage => CurrentPage > 1;
            public bool HasNextPage => CurrentPage < TotalPages;
    
            private static IQueryable<T> Search(IQueryable<T> query, string propertyName, 
                    string searchTerm) {
                var parameter = Expression.Parameter(typeof(T), "x");
                var source = propertyName.Split('.').Aggregate((Expression) parameter, 
                    Expression.Property);
                var body = Expression.Call(source, "Contains", Type.EmptyTypes, 
                    Expression.Constant(searchTerm, typeof(string)));
                var lambda = Expression.Lambda<Func<T, bool>>(body, parameter);
                return query.Where(lambda);
            }
    
            private static IQueryable<T> Order(IQueryable<T> query, string propertyName, 
                    bool desc) {
                var parameter = Expression.Parameter(typeof(T), "x");
                var source = propertyName.Split('.').Aggregate((Expression) parameter, 
                    Expression.Property);
                var lambda = Expression.Lambda(typeof(Func<,>).MakeGenericType(typeof(T), 
                    source.Type), source, parameter);
                return typeof(Queryable).GetMethods().Single(
                          method => method.Name == (desc ? "OrderByDescending" 
                                      : "OrderBy")
                          && method.IsGenericMethodDefinition
                          && method.GetGenericArguments().Length == 2
                          && method.GetParameters().Length == 2)
                      .MakeGenericMethod(typeof(T), source.Type)
                      .Invoke(null, new object[] { query, lambda }) as IQueryable<T>;
            }
        }
    }

public PagedList<Category> GetCategories(QueryOptions options) {
                return new PagedList<Category>(context.Categories, options);
            }

namespace SportsStore.Models.Pages {
    
        public class QueryOptions {
    
            public int CurrentPage { get; set; } = 1;
            public int PageSize { get; set; } = 10;
    
            public string OrderPropertyName { get; set; }
            public bool DescendingOrder { get; set; }
    
            public string SearchPropertyName { get; set; }
            public string SearchTerm { get; set; }
        }
    }

转载于:https://www.cnblogs.com/YrRoom/p/11070248.html