linq 常用语句

  自己练习的
  switch (productDataAnalysisQuery.DataType)
            {
                case 1:
                    var data = (from hp in GPEcontext.hbl_product
                                join hcim in
                                    from hci in GPEcontext.hbl_change_info
                                    where hci.LotNum == 0 && hci.ChangeData < 0
                                    && hci.CreatedTime >= beginDate && hci.CreatedTime <= endDate
                                    group hci by new { hci.ProductId } into G
                                    select new
                                    {
                                        ProductId = G.Key.ProductId,
                                        Amount = G.Sum(item => Math.Abs(item.ChangeData.Value))
                                    } on hp.id equals hcim.ProductId
                                orderby hcim.Amount descending
                                select new ProductDataAnalysisodel
                                {
                                    ProductName = hp.ProductName,
                                    ProductCode = hp.ProductCode,
                                    Amount = hcim.Amount
                                }).Take(20);
                    pageModel.Models = data.FindBy(item => true, productDataAnalysisQuery.PageNo, productDataAnalysisQuery.PageSize, out total, item => item.Amount, false);
                    break;
                case 2:
                    var data2 = (from hp in GPEcontext.hbl_product
                                 join hcim in
                                     from hci in GPEcontext.hbl_change_info
                                     where hci.LotNum == 0 && hci.ChangeData < 0
                                     && hci.CreatedTime >= beginDate && hci.CreatedTime <= endDate
                                     group hci by new { hci.ProductId } into G
                                     select new
                                     {
                                         ProductId = G.Key.ProductId,
                                         Amount = G.Sum(item => Math.Abs(item.ChangeData.Value))
                                     } on hp.id equals hcim.ProductId
                                 orderby hcim.Amount
                                 select new ProductDataAnalysisodel
                                 {
                                     ProductName = hp.ProductName,
                                     ProductCode = hp.ProductCode,
                                     Amount = hcim.Amount
                                 }).Take(20);
                    pageModel.Models = data2.FindBy(item => true, productDataAnalysisQuery.PageNo, productDataAnalysisQuery.PageSize, out total, item => item.Amount, false);
                    break;
                case 3:
                    var data3 = (from hp in GPEcontext.hbl_product
                                 join hcim in
                                     from hci in GPEcontext.hbl_change_info
                                     where hci.LotNum == 0 && hci.ChangeData < 0
                                     && hci.CreatedTime >= beginDate && hci.CreatedTime <= endDate
                                     group hci by new { hci.ProductId } into G
                                     select new
                                     {
                                         ProductId = G.Key.ProductId,
                                         Amount = G.Count()
                                     } on hp.id equals hcim.ProductId
                                 orderby hcim.Amount descending
                                 select new ProductDataAnalysisodel
                                 {
                                     ProductName = hp.ProductName,
                                     ProductCode = hp.ProductCode,
                                     Amount = hcim.Amount
                                 }).Take(20);
                    pageModel.Models = data3.FindBy(item => true, productDataAnalysisQuery.PageNo, productDataAnalysisQuery.PageSize, out total, item => item.Amount, false);

                    break;
                case 4:
                    var data4 = (from hp in GPEcontext.hbl_product
                                 join hcim in
                                     from hci in GPEcontext.hbl_change_info
                                     where hci.LotNum == 0 && hci.ChangeData < 0
                                     && hci.CreatedTime >= beginDate && hci.CreatedTime <= endDate
                                     group hci by new { hci.ProductId } into G
                                     select new
                                     {
                                         ProductId = G.Key.ProductId,
                                         Amount = G.Count()
                                     } on hp.id equals hcim.ProductId
                                 orderby hcim.Amount
                                 select new ProductDataAnalysisodel
                                 {
                                     ProductName = hp.ProductName,
                                     ProductCode = hp.ProductCode,
                                     Amount = hcim.Amount
                                 }).Take(20);
                    pageModel.Models = data4.FindBy(item => true, productDataAnalysisQuery.PageNo, productDataAnalysisQuery.PageSize, out total, item => item.Amount, false);

                    break;
                case 5:
                    var data5 = (from hp in GPEcontext.hbl_product
                                 join hs in
                                     from hps2 in GPEcontext.hbl_product_stock
                                     join p in
                                         from hps in GPEcontext.hbl_product_stock
                                         group hps by new { hps.ProductID } into G
                                         select new
                                         {
                                             ProductId = G.Key.ProductID,
                                             CreatedTime = G.Max(p => p.CreatedTime)
                                         }
                                     on new { A = hps2.ProductID, B = hps2.CreatedTime } equals new { A = p.ProductId, B = p.CreatedTime }
                                     select new
                                  {
                                      ProductId = hps2.ProductID,
                                      Amount = hps2.Stock
                                  }
                                             on hp.id equals hs.ProductId
                                 orderby hs.Amount descending
                                 select new ProductDataAnalysisodel
                                 {
                                     ProductName = hp.ProductName,
                                     ProductCode = hp.ProductCode,
                                     Amount = hs.Amount.Value
                                 }).Take(20);
                    pageModel.Models = data5.FindBy(item => true, productDataAnalysisQuery.PageNo, productDataAnalysisQuery.PageSize, out total, item => item.Amount, false);

                    break;
                case 6:
                    var data6 = (from hp in GPEcontext.hbl_product
                                 join hs in
                                     from hps2 in GPEcontext.hbl_product_stock
                                     join p in
                                         from hps in GPEcontext.hbl_product_stock
                                         group hps by new { hps.ProductID } into G
                                         select new
                                         {
                                             ProductId = G.Key.ProductID,
                                             CreatedTime = G.Max(p => p.CreatedTime)
                                         }
                                     on new { A = hps2.ProductID, B = hps2.CreatedTime } equals new { A = p.ProductId, B = p.CreatedTime }
                                     select new
                                     {
                                         ProductId = hps2.ProductID,
                                         Amount = hps2.Stock
                                     }
                                             on hp.id equals hs.ProductId
                                 orderby hs.Amount 
                                 select new ProductDataAnalysisodel
                                 {
                                     ProductName = hp.ProductName,
                                     ProductCode = hp.ProductCode,
                                     Amount = hs.Amount.Value
                                 }).Take(20);
                    pageModel.Models = data6.FindBy(item => true, productDataAnalysisQuery.PageNo, productDataAnalysisQuery.PageSize, out total, item => item.Amount, false);

                    break;
            }

Linq使用Group By 1
1.简单形式：

var q =  
from p in db.Products  
group p by p.CategoryID into g  
select g; 
语句描述：Linq使用Group By按CategoryID划分产品。

说明：from p in db.Products 表示从表中将产品对象取出来。group p by p.CategoryID into g表示对p按CategoryID字段归类。其结果命名为g，一旦重新命名，p的作用域就结束了，所以，最后select时，只能select g。

2.最大值

var q =  
from p in db.Products  
group p by p.CategoryID into g  
select new {  
g.Key,  
MaxPrice = g.Max(p => p.UnitPrice)  
}; 
语句描述：Linq使用Group By和Max查找每个CategoryID的最高单价。

说明：先按CategoryID归类，判断各个分类产品中单价最大的Products。取出CategoryID值，并把UnitPrice值赋给MaxPrice。

3.最小值

var q =  
from p in db.Products  
group p by p.CategoryID into g  
select new {  
g.Key,  
MinPrice = g.Min(p => p.UnitPrice)  
}; 
语句描述：Linq使用Group By和Min查找每个CategoryID的最低单价。

说明：先按CategoryID归类，判断各个分类产品中单价最小的Products。取出CategoryID值，并把UnitPrice值赋给MinPrice。

4.平均值

var q =  
from p in db.Products  
group p by p.CategoryID into g  
select new {  
g.Key,  
AveragePrice = g.Average(p => p.UnitPrice)  
}; 
语句描述：Linq使用Group By和Average得到每个CategoryID的平均单价。

说明：先按CategoryID归类，取出CategoryID值和各个分类产品中单价的平均值。

5.求和

var q =  
from p in db.Products  
group p by p.CategoryID into g  
select new {  
g.Key,  
TotalPrice = g.Sum(p => p.UnitPrice)  
}; 

今天遇到了一个问题，操作一个DataTable，DataTable的表结构如下：

Id,Name,Math,Chinese

此表对应的数据如下图：

要求合并后的效果如下图：

自己就想到了for循环的实现办法，也想用Linq可是不知道怎么写。后来msdn了一下，写出了如下的代码：

var query = from c in ds.Tables[0].AsEnumerable()  
            group c by c.Field<int>("Name")  
            into s  
            select new  
            {  
                ID = s.Select(m => m.Field<int>("ID").ToString()),  
                Name = s.Select(m => m.Field<string>("Name").ToString()),  
                Math = s.Sum(p => p.Field<decimal>("Math")),  
                Chinese = s.Sum(p => p.Field<decimal>("Chinese"))  
            };  

　　　　　　//法一:

 　　　　　　 DataTable tbl = tableA1.Clone();
            query.ToList().ForEach(p => tbl.Rows.Add(p.pingming, p.guige,p.biaohao,p.shuliang));

　　//法二:

　　　　DataTable dtss = new DataTable(); 
dtss.Columns.Add(new DataColumn("ID", typeof(string)));
 dtss.Columns.Add(new DataColumn("Name", typeof(string)));
 dtss.Columns.Add(new DataColumn("Math", typeof(string))); 
dtss.Columns.Add(new DataColumn("Chinese", typeof(string)));
 query.ToList().ForEach(p => dtss.Rows.Add(p.ID, p.Name, p.Math, p.Chinese ));

注意：linq结果可以用AsEnumerable立刻执行查询以及ToList ToArray转换成数组/集合