Linq与扩展方法

使用数据集

 /// <summary>
         /// 库房信息类
         /// </summary>
         public class Kfxx
         {
             /// <summary>
             /// 库房代码
             /// </summary>
             public string kfdm { get; set; }
             /// <summary>
             /// 库房名称
             /// </summary>
             public string kfmc { get; set; }
             /// <summary>
             /// 使用状态：0有效 1无效
             /// </summary>
             public int jlzt { get; set; }
         }
         /// <summary>
         /// 帐类信息类
         /// </summary>
         public class Zlxx
         {
             /// <summary>
             /// 库房代码
             /// </summary>
             public string kfdm { get; set; }
             /// <summary>
             /// 帐类代码
             /// </summary>
             public string zldm { get; set; }
             /// <summary>
             /// 帐类名称
             /// </summary>
             public string zlmc { get; set; }
             /// <summary>
             /// 金额
             /// </summary>
             public decimal je { get; set; }
         }
         /// <summary>
         /// 统计期信息类
         /// </summary>
         public class Tjqxx
         {
             /// <summary>
             /// 库房代码
             /// </summary>
             public string kfdm { get; set; }
             /// <summary>
             /// 帐类代码
             /// </summary>
             public string zldm { get; set; }
             /// <summary>
             /// 统计期
             /// </summary>
             public string ny { get; set; }
             /// <summary>
             /// 开始日期
             /// </summary>
             public DateTime ksrq { get; set; }
             /// <summary>
             /// 结束日期
             /// </summary>
             public DateTime jsrq { get; set; }
             /// <summary>
             /// 记账标志 0未记账 1已记账
             /// </summary>
             public int jzbz { get; set; }
             /// <summary>
             /// 金额
             /// </summary>
             public decimal je { get; set; }
         }

         /// <summary>
         /// 数据定义
         /// </summary>
         public class DataSource
         {
             public static List<Kfxx> kfxx { get; private set; }
             public static List<Kfxx> kfxx2 { get; private set; }
             public static List<Zlxx> zlxx { get; private set; }
             public static List<Tjqxx> tjqxx { get; private set; }
             static DataSource()
             {
                 kfxx = new List<Kfxx>
                 {
                     new Kfxx{kfdm="",kfmc="总务科",jlzt=},
                     new Kfxx{kfdm="",kfmc="设备科",jlzt=},
                     new Kfxx{kfdm="",kfmc="供应室",jlzt=},
                     new Kfxx{kfdm="",kfmc="总务科",jlzt=}
                 };
                 kfxx2 = new List<Kfxx>
                 {
                     new Kfxx{kfdm="",kfmc="Union库房",jlzt=}
                 };
                 zlxx = new List<Zlxx>
                 {
                     new Zlxx{kfdm="",zldm="",zlmc="医用材料",je=},
                     new Zlxx{kfdm="",zldm="",zlmc="一次性材料",je=},
                     new Zlxx{kfdm="",zldm="",zlmc="器械材料",je=},
                     new Zlxx{kfdm="",zldm="",zlmc="无统计期",je=}
                 };
                 tjqxx = new List<Tjqxx>
                 {
                     new Tjqxx{kfdm="",zldm="",ny="",ksrq=Convert.ToDateTime("2013-06-01 00:00:00"),jsrq=Convert.ToDateTime("2013-06-30 23:59:59"),jzbz=,je=},
                     new Tjqxx{kfdm="",zldm="",ny="",ksrq=Convert.ToDateTime("2013-07-01 00:00:00"),jsrq=Convert.ToDateTime("2013-07-31 23:59:59"),jzbz=,je=},
                     new Tjqxx{kfdm="",zldm="",ny="",ksrq=Convert.ToDateTime("2013-07-01 00:00:00"),jsrq=Convert.ToDateTime("2013-07-31 23:59:59"),jzbz=,je=},
                     new Tjqxx{kfdm="",zldm="",ny="",ksrq=Convert.ToDateTime("2013-07-01 00:00:00"),jsrq=Convert.ToDateTime("2013-07-31 23:59:59"),jzbz=,je=}
                 };
             }
         }

数据集

1.简单查询

var Query = from a in DataSource.kfxx
                        where a.kfdm==""
                        select new
                        {
                            a.kfdm,
                            a.kfmc
                        };

var Query = DataSource.kfxx.Select(p => new { p.kfdm, p.kfmc }).Where(p => p.kfdm == "");

2.distinct,first,last,skip,take,single

var Query = DataSource.kfxx.Select(p => new { p.kfdm, p.kfmc }).Distinct();
var Query = DataSource.kfxx.Select(p => new { p.kfdm, p.kfmc }).First();
var Query = DataSource.kfxx.Select(p => new { p.kfdm, p.kfmc }).Last();
var Query = DataSource.kfxx.Select(p => new { p.kfdm, p.kfmc }).Skip();
var Query = DataSource.kfxx.Select(p => new { p.kfdm, p.kfmc }).Take();
var Query = DataSource.kfxx.Where(p => p.kfdm == "").Select(p => new { p.kfdm, p.kfmc }).Single();

扩展方法

3.排序

var Query = from a in DataSource.kfxx
                        orderby a.kfdm descending, a.jlzt
                        select new
                        {
                            a.kfdm,
                            a.jlzt
                        };

var Query = DataSource.kfxx.OrderByDescending(p => p.kfdm).ThenBy(p => p.jlzt).Select(p => new { p.kfdm, p.jlzt });

4.Join

4.1 inner join

var Query = from a in DataSource.kfxx
                        from b in DataSource.zlxx
                        where a.jlzt ==  && a.kfdm==b.kfdm
                        orderby a.kfdm descending, a.jlzt
                        select new
                        {
                            a.kfdm,
                            a.kfmc,
                            b.zldm,
                            b.zlmc
                        };

var Query = (DataSource.zlxx.Join(DataSource.kfxx.Where(q => q.jlzt == ),
                p => p.kfdm, q => q.kfdm,
                (p, q) => new { q.kfdm, q.kfmc, p.zldm, p.zlmc, q.jlzt }))
                .OrderByDescending(s => s.kfdm).ThenBy(s => s.jlzt)
                .Select(t => new { t.kfdm, t.kfmc, t.zldm, t.zlmc });

4.2 left join

var Query = from a in DataSource.kfxx
                        from b in DataSource.zlxx
                        join c in DataSource.tjqxx on new { kfdm = b.kfdm, zldm = b.zldm } equals new { kfdm = c.kfdm, zldm = c.zldm }
                        into gg
                        from g in gg.DefaultIfEmpty()
                        where a.jlzt ==  && a.kfdm == b.kfdm && (g == null ?  : g.jzbz) ==
                        //orderby a.kfdm descending, a.jlzt
                        select new
                        {
                            a.kfdm,
                            a.kfmc,
                            b.zldm,
                            b.zlmc,
                            ny = g == null ? "" : g.ny,
                            ksrq = g == null ? "" : g.ksrq.ToString(),
                            jsrq = g == null ? "" : g.jsrq.ToString()
                        };

var Query = (DataSource.zlxx.Join(DataSource.kfxx.Where(q => q.jlzt == ),
                    p => p.kfdm, q => q.kfdm,
                    (p, q) => new { q.kfdm, q.kfmc, p.zldm, p.zlmc }))
                .GroupJoin(DataSource.tjqxx.Where(tjq=>tjq.jzbz==), zl => new { zl.kfdm, zl.zldm }, tjq => new { tjq.kfdm, tjq.zldm },
                    (zl, tjq) => new
                    {
                        zl = zl,
                        tjq = tjq
                    })
                .SelectMany(group => group.tjq.DefaultIfEmpty(),
                    (group, tjq) => new
                    {
                        group.zl.kfdm,
                        group.zl.kfmc,
                        group.zl.zldm,
                        group.zl.zlmc,
                        ny = tjq == null ? "" : tjq.ny,
                        ksrq = tjq == null ? "" : tjq.ksrq.ToString(),
                        jsrq = tjq == null ? "" : tjq.jsrq.ToString()
                    }
                );

5.聚合(count,sum,max,min,avg)

var Query = from a in DataSource.kfxx
                        join b in DataSource.zlxx on a.kfdm equals b.kfdm
                        into gg
                        where a.jlzt ==
                        from g in gg.DefaultIfEmpty()
                        group g by a.kfdm into gg1
                        where gg1.Sum(p => p == null ?  : p.je)>
                        select new
                        {
                            kfdm = gg1.Key,
                            zlcount = gg1.Count(p => (p == null ? "" : p.zldm) != ""),
                            zje = gg1.Sum(p => p == null ?  : p.je),
                            je_min = gg1.Min(p => p == null ?  : p.je),
                            je_max = gg1.Max(p => p == null ?  : p.je),
                            je_avg = gg1.Average(p => p == null ?  : p.je)
                        };

var Query = DataSource.kfxx.Where(g => g.jlzt == ).GroupJoin(DataSource.zlxx, kf => kf.kfdm, zl => zl.kfdm,
                    (kf, zl) => new
                    {
                        kfdm = kf.kfdm,
                        zlcount = zl.DefaultIfEmpty().Count(p => (p == null ? "" : p.zldm) != ""),
                        zje = zl.DefaultIfEmpty().Sum(p => p == null ?  : p.je),
                        je_min = zl.DefaultIfEmpty().Min(p => p == null ?  : p.je),
                        je_max = zl.DefaultIfEmpty().Max(p => p == null ?  : p.je),
                        je_avg = zl.DefaultIfEmpty().Average(p => p == null ?  : p.je)
                    }).Where(g=>g.zje>);

6.其他

6.1 Union

var Query = DataSource.kfxx.Union(DataSource.kfxx2);

6.2 自定义聚合Aggregate

//自定义求平均为例
            var Query = DataSource.kfxx.Where(g => g.jlzt == ).GroupJoin(DataSource.zlxx, kf => kf.kfdm, zl => zl.kfdm,
                    (kf, zl) => new
                    {
                        kfdm = kf.kfdm,
                        je_avg0 = zl.DefaultIfEmpty().Average(p => p == null ?  : p.je),
                        je_avg1 = zl.DefaultIfEmpty().Aggregate(new Zlxx {je=},
                            (a, b) => { return new Zlxx { je = (a == null ?  : a.je) + (b == null ?  : b.je) }; },
                            c => new Zlxx { je = (c == null ?  : c.je )/ (zl.DefaultIfEmpty().Count(p => (p == null ? "" : p.zldm) != "") ==  ?  : (zl.DefaultIfEmpty().Count(p => (p == null ? "" : p.zldm) != ""))) }).je.ToString("C")
                    });

源代码(http://download.csdn.net/detail/lk13962517093/5692997)

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