• Linq通用分页数据查询方法

    在使用EF的过程有很多需要分页查询数据的地方，但是经常重复在输入分页的相关代码，这样即不便于维护，也增加了不少工作量。

    对于通用查询有几个要点，一是要动态定义查询条件，还可以动态选择所需要的列。

    1、数据查询方法

    Code Snippet
    1. publicstaticList<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query,
    2.                                                                       Expression<Func<TEntity, bool>> where,
    3.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
    4.                                                                       Expression<Func<TEntity, int, TResult>> selector,
    5.                                                                       bool isAsc)
    Code Snippet
    1. publicstaticList<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query,
    2.                                                                       Expression<Func<TEntity, bool>> where,
    3.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
    4.                                                                       Func<IQueryable<TEntity>, List<object>> selector,
    5.                                                                       bool isAsc)
    Code Snippet
    1. publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
    2.                                                                 Expression<Func<TEntity, bool>> where,
    3.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
    4.                                                                 Func<IQueryable<TEntity>, List<object>> selector,
    5.                                                                 bool isAsc)

    3、分页查询方法

    Code Snippet
    1. publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
    2.                                                          List<Expression<Func<TEntity, bool>>> wheres,
    3.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
    4.                                                          Func<IQueryable<TEntity>, List<object>> selector, bool isAsc)
    Code Snippet
    1. publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
    2.                                                          List<Expression<Func<TEntity, bool>>> wheres,
    3.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
    4.                                                          Func<IQueryable<TEntity>, List<TResult>> selector, bool isAsc)
    Code Snippet
    1. publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
    2.                                                                 Expression<Func<TEntity, bool>> where,
    3.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
    4.                                                                 Func<IQueryable<TEntity>, List<TResult>> selector,
    5.                                                                 bool isAsc)

    工具类方法：

    Code Snippet
    1. publicclassPageInfo
    2.     {
    3.         publicstaticvoid CheckPageIndexAndSize(refint index, refint size)
    4.         {
    5.             if (index < 1)
    6.             {
    7.                 index = 1;
    8.             }
    9.  
    10.             if (size < 1)
    11.             {
    12.                 size = 20;
    13.             }
    14.         }
    15.  
    16.         publicstaticvoid CheckPageIndexAndSize(refint index, int size, int count)
    17.         {
    18.             if (count >= index * size)
    19.             {
    20.                 return;
    21.             }
    22.  
    23.             index = count / size;
    24.             if (count % size > 0)
    25.             {
    26.                 index++;
    27.             }
    28.  
    29.             if (index == 0)
    30.             {
    31.                 index = 1;
    32.             }
    33.         }
    34.  
    35.     }
    36.  
    37.     publicclassPageInfo<T> : PageInfo
    38.     {
    39.         internal PageInfo()
    40.         {
    41.             DataList = newList<T>();
    42.         }
    43.         public PageInfo(int index, int pageSize, int count, List<T> dataList)
    44.         {
    45.             Index = index;
    46.             PageSie = pageSize;
    47.             Count = count;
    48.             DataList = dataList;
    49.         }
    50.  
    51.         publicint Index { get; privateset; }
    52.         publicint PageSie { get; privateset; }
    53.         publicint Count { get; privateset; }
    54.         publicList<T> DataList { get; privateset; }
    55.  
    56.         publicPageInfo<T> Empty
    57.         {
    58.             get { returnnewPageInfo<T>(); }
    59.         }
    60.     }

    实现代码：

    Code Snippet
    1. publicstaticclassLinqExtent
    2.     {
    3.         publicstaticList<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query,
    4.                                                                       Expression<Func<TEntity, bool>> where,
    5.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
    6.                                                                       Expression<Func<TEntity, int, TResult>> selector,
    7.                                                                       bool isAsc)
    8.         {
    9.             if (selector == null)
    10.             {
    11.                 thrownewArgumentNullException("selector");
    12.             }
    13.  
    14.             var queryable = query;
    15.             if (where != null)
    16.             {
    17.                 queryable = queryable.Where(where);
    18.             }
    19.             if (orderby != null)
    20.             {
    21.                 queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
    22.             }
    23.  
    24.             return queryable.Select(selector).ToList();
    25.         }
    26.  
    27.         publicstaticList<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query,
    28.                                                                       Expression<Func<TEntity, bool>> where,
    29.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
    30.                                                                       Func<IQueryable<TEntity>, List<object>> selector,
    31.                                                                       bool isAsc)
    32.         {
    33.             if (selector == null)
    34.             {
    35.                 thrownewArgumentNullException("selector");
    36.             }
    37.  
    38.             var queryable = query;
    39.             if (where != null)
    40.             {
    41.                 queryable = queryable.Where(where);
    42.             }
    43.             if (orderby != null)
    44.             {
    45.                 queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
    46.             }
    47.  
    48.             return selector(queryable);
    49.         }
    50.  
    51.         publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
    52.                                                                 Expression<Func<TEntity, bool>> where,
    53.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
    54.                                                                 Func<IQueryable<TEntity>, List<object>> selector,
    55.                                                                 bool isAsc)
    56.         {
    57.             return Query(query, index, pageSize, newList<Expression<Func<TEntity, bool>>> {where}, orderby, selector,
    58.                          isAsc);
    59.         }
    60.         publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
    61.                                                          List<Expression<Func<TEntity, bool>>> wheres,
    62.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
    63.                                                          Func<IQueryable<TEntity>, List<object>> selector, bool isAsc)
    64.         {
    65.             //if (selector == null)
    66.             //{
    67.             //    throw new ArgumentNullException("selector");
    68.             //}
    69.  
    70.             //PageInfo.CheckPageIndexAndSize(ref index,ref pageSize);
    71.             //IQueryable<TEntity> queryable = query;
    72.             //if (wheres != null)
    73.             //{
    74.             //    wheres.ForEach(p=>queryable = queryable.Where(p));
    75.             //}
    76.  
    77.             //int count = query.Count();
    78.             //PageInfo.CheckPageIndexAndSize(ref index,pageSize,count);
    79.             //if (count > 0)
    80.             //{
    81.             //    if (orderby != null)
    82.             //    {
    83.             //        queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
    84.  
    85.             //    }
    86.  
    87.             //    return new PageInfo<object>(index,pageSize,count,selector(queryable));
    88.             //}
    89.  
    90.             //return new PageInfo<object>(index,pageSize,count,new List<object>());
    91.  
    92.             return Query<TEntity, TOrderBy, object>(query, index, pageSize, wheres, orderby, selector, isAsc);
    93.         }
    94.  
    95.         publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
    96.                                                          List<Expression<Func<TEntity, bool>>> wheres,
    97.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
    98.                                                          Func<IQueryable<TEntity>, List<TResult>> selector, bool isAsc)
    99.         {
    100.             if (selector == null)
    101.             {
    102.                 thrownewArgumentNullException("selector");
    103.             }
    104.  
    105.             PageInfo.CheckPageIndexAndSize(ref index, ref pageSize);
    106.             IQueryable<TEntity> queryable = query;
    107.             if (wheres != null)
    108.             {
    109.                 wheres.ForEach(p => queryable = queryable.Where(p));
    110.             }
    111.  
    112.             int count = query.Count();
    113.             PageInfo.CheckPageIndexAndSize(ref index, pageSize, count);
    114.             if (count > 0)
    115.             {
    116.                 if (orderby != null)
    117.                 {
    118.                     queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
    119.  
    120.                 }
    121.  
    122.                 returnnewPageInfo<TResult>(index, pageSize, count, selector(queryable));
    123.             }
    124.  
    125.             returnnewPageInfo<TResult>(index, pageSize, count, newList<TResult>());
    126.         }
    127.  
    128.         publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
    129.                                                                 Expression<Func<TEntity, bool>> where,
    130.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
    131.                                                                 Func<IQueryable<TEntity>, List<TResult>> selector,
    132.                                                                 bool isAsc)
    133.         {
    134.             return Query(query, index, pageSize, newList<Expression<Func<TEntity, bool>>> { where }, orderby, selector,
    135.                          isAsc);
    136.         }
    137.     }
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  • 原文地址：https://www.cnblogs.com/LifelongLearning/p/2867491.html
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