Lind.DDD.Paging分页模块介绍

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分页组件网上有很多，MVC.Pager，JSPager等，通过实现方式大体分为前端分页和后端分页，前端分页是前台对list内存本地集合进行分页，缺点就是在大数据情况下，内存占用过高；后端分页就是ＵＩ把要返回的页号告诉后台，由后台组织数据并返回，这种方法就是我们经常看到的了；而根据后台集合种类又可以分类List和IQueryable，前者是本地集合，在返回数据时，直接把第几页共几条的集合返回；IQueryable是预查询集合，它是Linq的产物，在很多地里它不通用，除非你的ＯＲＭ框架支持Linq，否则建议用List本地集合，一般来说，分页的本地集合会在底层提供一些方法，它的参数一般包含了pageIndex和pageSize，下面可以看一下大叔针对mongodb制定的分页规范

 　　　  /// <summary>
        /// MongoDB集成的查询方法，大数据情况下，有分页时使用这个方法
        /// </summary>
        /// <typeparam name="U">匿名对象，用来为条件赋值</typeparam>
        /// <param name="template">条件对象</param>
        /// <param name="limit"></param>
        /// <param name="skip"></param>
        /// <returns></returns>
        PagedResult<TEntity> GetModel<U>(U template, int pageIndex, int pageSize);

而在Linq的底层，可以直接返回IQueryable集合，而在业务层进行返回Lind.DDD.Paging的分页集合即可，这块比较方便，今天主要说的是Linq下的分页方法

　　　　 /// <summary>
        /// 拿到可查询结果集(Linq)
        /// </summary>
        /// <returns></returns>
        System.Linq.IQueryable<TEntity> GetModel();

LINQ环境下大叔分页的介绍

分页基类

 public abstract class PageListBase<T> :
        List<T>,
        IEnumerable<T>,
        IPagedList //繼承List<T>可以使用它的内部方法，如AddRange,Skip,Take等
    {
        /// <summary>
        /// 初始化分页
        /// </summary>
        public PageListBase()
        {
            this.AddParameters = new NameValueCollection();
            this.PageSize = ;
        }

        /// <summary>
        /// 总页数
        /// </summary>
        public int TotalPages { get; set; }

        /// <summary>
        /// 总记录数
        /// </summary>
        public int TotalCount { get; set; }

        /// <summary>
        /// 当前页
        /// </summary>
        public int PageIndex { get; set; }

        /// <summary>
        /// 每页显示多少条记录
        /// </summary>
        public int PageSize { get; set; }

        /// <summary>
        /// 是否有上一页
        /// </summary>
        public bool IsPreviousPage { get { return (PageIndex > ); } }

        /// <summary>
        /// 是否有下一页
        /// </summary>
        public bool IsNextPage { get { return (PageIndex * PageSize) <= TotalCount; } }

        /// <summary>
        /// 分页参数
        /// </summary>
        public NameValueCollection AddParameters { get; set; }
    }

对于分页我们提供了传统分页和微博式（加载更多）分页，它们有自己的返回对象，看一下代码

   　/// <summary>
    /// 分页通用类(传统分页)
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class PagedList<T> : PageListBase<T>
    {
        public PagedList()
            : this(null, , )
        {
        }
        /// <summary>
        /// 数据源为IQueryable的范型
        /// </summary>
        /// <param name="source">数据源</param>
        /// <param name="index">当前页</param>
        /// <param name="pageSize">每页显示多少条记录</param>
        public PagedList(IQueryable<T> source, int index, int pageSize)
        {
            if (source != null) //判断传过来的实体集是否为空
            {
                int total = source.Count();
                this.TotalCount = total;
                this.TotalPages = total / pageSize;

                if (total % pageSize > )
                    TotalPages++;

                this.PageSize = pageSize;
                if (index > this.TotalPages)
                {
                    index = this.TotalPages;
                }
                if (index < )
                {
                    index = ;
                }
                this.PageIndex = index;
                this.AddRange(source.Skip((index - ) * pageSize).Take(pageSize).ToList()); //Skip是跳到第几页，Take返回多少条
            }
        }
    }

微博式分页主要是在原有数据基础上，进行追加数据，这在Linq里相当于一个Skip(0)加Take(PageIndex*PageSize)的动作，呵呵

    /// <summary>
    /// 以追加的方式，显示内容，即从第1页开始显示N条记录
    /// </summary>
    /// <typeparam name="T"></typeparam>
     public class PageListAppend<T> : PageListBase<T>
    {
        /// <summary>
        /// 数据源为IQueryable的范型
        /// </summary>
        /// <param name="source">数据源</param>
        /// <param name="index">当前页</param>
        /// <param name="pageSize">每页显示多少条记录</param>
        public PageListAppend(IQueryable<T> source, int index, int pageSize)
        {
            if (source != null) //判断传过来的实体集是否为空
            {
                int total = source.Count();
                this.TotalCount = total;
                this.TotalPages = total / pageSize;

                if (total % pageSize > )
                    TotalPages++;

                this.PageSize = pageSize;
                if (index > this.TotalPages)
                {
                    index = this.TotalPages;
                }
                if (index < )
                {
                    index = ;
                }
                this.PageIndex = index;
                this.AddRange(source.Skip().Take(index * pageSize).ToList()); //Skip是跳到第几页，Take返回多少条
            }
        }
    }

有一点要特别注意一下，在LINQ分页时，我们看到被传入的集合一定是IQueryable的，如果是本地IList集合，那就失去了分页的意义，它相当于把所有数据加载到内存，然后再分页了。

有了数据的返回，下面再来看一下前台页面的组织，我们也封装了一个PagerHelper的方法，当然你也可以在分部页上进行设计，这都是可以的。

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alt="" />

我们在前台调用时为大家封装了ajax分页，传统分页和微博分页等，直接在view上调用即可，当然如果你在前台对样式要求比较严格，也可以自己设计分布页来实现

@{
    //分页灵活视图，根据自己项目的需要，去重写它
    Layout = null;
    var route = Request.RequestContext.RouteData.Values;
    var controller = route["controller"].ToString();
    var action = route["action"].ToString();
    var currentPage = int.Parse((route["page"] ?? Request.QueryString["page"] ?? "").ToString());

    var pageCount = int.Parse((route["pageCount"] ?? Request.QueryString["pageCount"] ?? "").ToString());
    if (currentPage < )
    {
        currentPage = ;
    }
    if (currentPage > pageCount)
    {
        currentPage = pageCount;
    }
}
<div>
    <span>@Html.ActionLink("首页", action, controller, new { page =  })</span>
    <span>@Html.ActionLink("上一页", "Index", new { page = currentPage -  })</span>
    <span>@Html.ActionLink("下一页", "Index", new { page = currentPage +  })</span>
    <span>@Html.ActionLink("尾页", "Index", new { page = pageCount })</span>
    <span>@currentPage/@pageCount</span>
</div>

感谢各位的耐心阅读！

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