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LINQ查询返回DataTable类型

2018-06-17 19:51:59来源：未知阅读 ()

个人感觉Linq实用灵活性很大，参考一篇大牛的文章LINQ查询返回DataTable类型

http://xuzhihong1987.blog.163.com/blog/static/26731587201101853740294/

附上自己写的一个测试程序源代码。

下载

  //创建自定义DataTable
             String[] _sFiled = new String[] { "ID", "PC", "EPC", "CRC", "RSSI", "FREQANT", "INVCOUNT" };
# region Linq写法
             //  LinQ写法1：
             //var numbers_1 = from number in numbers where (number % 2 == 0) orderby number descending select number;//orderby number descending 这是对筛选出来的数值进行排序
             //   foreach (var i in numbers_1) 
             //   { 
             //   Console.WriteLine(i); 
             //   }
             //LinQ写法2：
             //  var numbers_1 = numbers.Where(i => i % 2 == 0).Select(i => i);//输出用写法1一样
#endregion
            
             DataTable    _dtAudit = CreateSelfDataTable(_sFiled);

             _dtAudit.Rows.Add("a1", "b1", "c1","","","","");
             _dtAudit.Rows.Add("a1", "b2", "c2", "", "", "", "");
             _dtAudit.Rows.Add("a2", "b3", "c3", "", "", "", "");
             _dtAudit.Rows.Add("a3", "b4", "c4", "", "", "", "");
             _dtAudit.Rows.Add("a1", "b5", "c5", "", "", "", "");
             _dtAudit.Rows.Add("a2", "b6", "c6", "", "", "", "");

             var query1 = (from contact in _dtAudit.AsEnumerable()                                      //查询
                           orderby contact.Field<string>("ID") descending                                      //排序
                           group contact by contact.Field<string>("PC") into g                               //分组
                           select new {ID=g.FirstOrDefault().Field<string>("ID"),PC=g.FirstOrDefault().Field<string>("PC"),EPC=
                               g.FirstOrDefault().Field<string>("EPC"),CRC=g.FirstOrDefault().Field<string>("CRC"),RSSI=g.FirstOrDefault(
                               ).Field<string>("RSSI")}).ToList();
            DataTable contacts1 =ToDataTable(query1);
           SetListView(listView1, contacts1);
        }

        /// <summary>
        /// 创建自定义列DataTable
        /// </summary>
        /// <param name="sList"></param>
        /// <returns></returns>
        public    DataTable CreateSelfDataTable(String[] sList)
        {
            DataTable _dtSelf = new DataTable();

            foreach (String s in sList)
            {
                _dtSelf.Columns.Add(s);
            }
            _dtSelf.AcceptChanges();

            return _dtSelf;
        }
          


/// <summary>
 ///  下面通过一个方法来实现返回DataTable类型 
 /// LINQ返回DataTable类型
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="varlist"></param>
/// <returns></returns>
        public static DataTable ToDataTable<T>(IEnumerable<T> varlist)
        {
            DataTable dtReturn = new DataTable();
            // column names 
            PropertyInfo[] oProps = null;
            if (varlist == null)
                return dtReturn;
            foreach (T rec in varlist)
            {
                if (oProps == null)
                {
                   oProps = ((Type)rec.GetType()).GetProperties();
                    foreach (PropertyInfo pi in oProps)
                    {
                        Type colType = pi.PropertyType;
                        if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition()
                             == typeof(Nullable<>)))
                        {
                            colType = colType.GetGenericArguments()[0];
                        }
                        dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
                    }
                }
                DataRow dr = dtReturn.NewRow();
                foreach (PropertyInfo pi in oProps)
                {
                    dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue
                    (rec, null);
                }
                dtReturn.Rows.Add(dr);
            }
            return dtReturn;
        }

        /// <summary>
        /// 绑定ListView
        /// </summary>
        private void SetListView(System.Windows.Forms.ListView listView, DataTable dt)
        {
            if (listView.Items.Count > 50)
            {
                listView.Items.Clear();
            }
            if (dt != null && dt.Rows.Count > 0)
            {
                ListViewItem lv = null;
                for (int i = 0; i < dt.Rows.Count; i++)
                {
                    lv = new ListViewItem(dt.Rows[i][0].ToString());                           //创建一列的多行对象
                    lv.Tag = dt.Rows[i][0].ToString();                                         //该lv对象绑定多行一列值
                    for (int j = 1; j < dt.Columns.Count; j++)
                    {
                        lv.SubItems.Add(dt.Rows[i][j].ToString());                             //一行添加多列的值
                    }
                    listView.Items.Add(lv);
                }

            }
        }

View Code

LINQ基本语法及其示例

http://xuzhihong1987.blog.163.com/blog/static/26731587201111342756123/

说明：

1、在未作任何说明的情况下，以下用到的db变量都是DataContext的实例对象，声明语法类似如下：

using (BP_DataClassesDataContext db = new BP_DataClassesDataContext(ConnectionStrings.GetInstance("ZJ").Con))

{

//Code

}

2、默认q为Iqueryable类型变量

简单查询：

var q = from p in db.view_PreTestResultAuditList

select p;

简单条件查询：

方式一：直接使用where关键字

var q = from c in db.view_PrTestList

where c.FTestmanID.Equals(UserContext.CurrentUser.FID)

select c;

方式二：使用lambda 表达式

var q = db.TOriInfoAutoMemory.Where(c => c.FSampleName == sampleName);

使用 &&和|| 带代替And或Or关键字：

var entity = db.TSampleOriginalInfo.FirstOrDefault(c => c.FFromID.Equals(fromID) && c.FSampleID.Equals(sampleID));

like模糊条件查询：

//使用C#中的Contains关键字代替SQL中的like关键字

q = q.Where(c => c.FTaskCode.Contains(condition.Name));

In包含查询：

/// <param name="certificateIDs"> string[] </param>

var certi = (from c in db.TMSCertificate

where certificateIDs.ToList().Contains(c.FID.ToString())

select c).ToList();

等价于：select * from TMSCertificate where FID in /* certificateIDs */

Skip和Take实现分页查询：

var q = from c in db.view_PrTestList

where c.FTestmanID.Equals(UserContext.CurrentUser.FID)

select c;

twi.data = (q.Skip(paging.startIndex).Take(paging.pageSize)).ToList();

//其中startIndex：跳过的系列中指定的条数

// pageSize：每页显示条数（记录数）

Distinct方法去除重复：

var p = (from c in dc.TSampleOriginalInfo

where sampleIDs.Contains(c.FSampleID.ToString())

select new

{

c.FFromID,

c.FName

}).Distinct();

查询指定列使new构造集合：

var p = (from c in dc.TSampleOriginalInfo

where sampleIDs.Contains(c.FSampleID.ToString())

select new

{

c.FFromID,

c.FName

}).Distinct();

join连接查询：详见下面的【join查询实例】

//此处省略……

FirstOrDefault查询满足条件的第一条记录或不存在是返回null，不发生异常：

foreach (var fromID in fromIDs)

{

var entity = db.TSampleOriginalInfo.FirstOrDefault(c => c.FFromID.Equals(fromID) && c.FSampleID.Equals(sampleID));

if (entity != null)

{

entities.Add(entity);

}

LINQ to SQL 的重要方法：SubmitChanges方法：

无论您对对象做了多少项更改，都只是在更改内存中的副本。您并未对数据库中的实际数据做任何更改。直到您对 DataContext 显式调用 SubmitChanges方法，您所做的更改才会传输到服务器。

db.SubmitChanges();

新增/删除/修改后都需要显式的调用该方法！

以下是示例代码

      /// <summary>

        /// 添加

        /// </summary>

        /// <param name="varCustomer">要添加的对象</param>

        /// <returns></returns>

        public bool New(TTrademark idc)

        {

            using (CP_DataClassesDataContext db = new CP_DataClassesDataContext(GS.MODEL.ConnectionStrings.GetInstance("ZJ").Con))

            {

                if (idc != null)

                {

                    db.TTrademark.InsertOnSubmit(idc);

                    db.SubmitChanges();

                    return true;

                }

                else

                {

                    return false;

                }

            }

        }

       /// <summary>

       /// 新增多个【使用InsertAllOnSubmit】

       /// </summary>

       /// <param name="model"></param>

       public void New(GS.MODEL.TItem model)

       {

           using (CP_DataClassesDataContext db = new CP_DataClassesDataContext(GS.MODEL.ConnectionStrings.GetInstance("ZJ").Con))

           {

               List<GS.MODEL.TItem> entities = new List<GS.MODEL.TItem>();

               GS.MODEL.TItem entity = new GS.MODEL.TItem()

               {

                   FID = Guid.NewGuid(),

                   FName =model.FName ,

                   FParentName = model.FParentName,

                   FFastCode = model.FFastCode,

                   FRemark=model.FRemark,

                   FSort=model.FSort

               };

               entities.Add(entity);

               db.TItem.InsertAllOnSubmit(entities);

               db.SubmitChanges();

           }

       }

 

 

       /// <summary>

       /// 修改

       /// </summary>

       /// <param name="model"></param>

       public void Edit(GS.MODEL.TItem model)

       {

          using(CP_DataClassesDataContext db=new CP_DataClassesDataContext(GS.MODEL.ConnectionStrings.GetInstance("ZJ").Con))

          {

              GS.MODEL.TItem items = db.TItem.Single(c => c.FID == model.FID);

              items.FName = model.FName;

              items.FParentName = model.FParentName;

              items.FRemark = model.FRemark;

              items.FSort = model.FSort;

              items.FFastCode = model.FFastCode;

              db.SubmitChanges();

          }

       }

 

       /// <summary>

       /// 删除

       /// </summary>

       /// <param name="IDs"></param>

       public void Delete(string[] ids)

       {

           using (CP_DataClassesDataContext db = new CP_DataClassesDataContext(GS.MODEL.ConnectionStrings.GetInstance("ZJ").Con))

           {

               List<GS.MODEL.TItem> entities = new List<GS.MODEL.TItem>();

               foreach (var id in ids)

               {

                   var entity = db.TItem.FirstOrDefault(c => c.FID.Equals(id));

                       if (entity != null)

                       {

                           entities.Add(entity);

                       }

               }

               db.TItem.DeleteAllOnSubmit(entities);

               db.SubmitChanges();

           }

       }

 

 

        /// <summary>

        /// 【简单查询】获取指定计量标准考核证书下的计量标准器/检定规程/主要配套设备

        /// </summary>

        /// <param name="certifiacteID"></param>

        /// <returns></returns>

        public IList<view_CertificateOriginalInfo> GetViewByCertificateID(Guid certifiacteID)

        {

            using (BPDataContext db = new BPDataContext(TCTC_ConnectionStrings.connStrJL))

            {

                var d = from c in db.view_CertificateOriginalInfo

                        where c.FCertificateID == certifiacteID

                        select c;

                return d.ToList();

            }

        }

 

 

        /// <summary>

        /// 【综合查询】我的待检测结果任务单

        /// </summary>

        /// <param name="paging"></param>

        /// <param name="condition"></param>

        /// <returns></returns>

        public TwiReturn GetMyWorkList(PagingCondition paging, ConditionModel condition)

        {

            TwiReturn twi = new TwiReturn();

            using (BP_DataClassesDataContext db = new BP_DataClassesDataContext(ConnectionStrings.GetInstance("ZJ").Con))

            {

                var q = from c in db.view_PrTestList

                        where c.FTestmanID.Equals(UserContext.CurrentUser.FID)

                        select c;

                if (condition != null)

                {

                    if (condition.NameSign == "TaskCode" && condition.Name != "")

                    {

                        q = q.Where(c => c.FTaskCode.Contains(condition.Name));

                    }

                    else if (condition.NameSign == "TestItemName" && condition.Name != "")

                    {

                        q = q.Where(c => c.FTestItemName.Contains(condition.Name));

                    }

                }

                twi.totalCount = q.Count();

                if (paging.needPaging)

                {

                    twi.data = (q.Skip(paging.startIndex).Take(paging.pageSize)).ToList();

                }

                else

                {

                    twi.data = q.ToList();

                }

                return twi;

            }

        }

 

 

        /// <summary>

        /// 选择计量标准考核证书

        /// </summary>

        /// <param name="sampleIDs"></param>

        /// <param name="certificateIDs"></param>

        public void SelectCertificate(string[] sampleIDs, string[] certificateIDs)

        {

            BPDataContext bpDC = new BPDataContext(TCTC_ConnectionStrings.connStrJL);

            CPDataContext cpDc = new CPDataContext(TCTC_ConnectionStrings.connStrJL);

            var certi = (from c in cpDc.TMSCertificate

                         where certificateIDs.ToList().Contains(c.FID.ToString())

                         select c).ToList();

            List<TSampleOriginalInfo> entities = new List<TSampleOriginalInfo>();

            foreach (var sampleID in sampleIDs)

            {

                foreach (var c in certi)

                {

                    TSampleOriginalInfo entity = new TSampleOriginalInfo()

                    {

                        FID = Guid.NewGuid(),

                        FFromID = c.FID,

                        FType = 1,

                        FSampleID = new Guid(sampleID),

                        FName = c.FCertificateName,

                        FCode = c.FCode,

                        FRange = c.FMeasurementRange,

                        FUncertainty = c.FLevel,

                        FCertificateNo = c.FCode,//c.FNumber,zjw修改

                        FValidDateTo = c.FPeriodDate

                    };

                    entities.Add(entity);

                }

            }

            bpDC.TSampleOriginalInfo.InsertAllOnSubmit(entities);

            bpDC.SubmitChanges();

            bpDC.Dispose();

            cpDc.Dispose();

        }

 

 

        /// <summary>

        /// 获取样品之标准/计量标准器/主要配套设备/检定规程

        /// </summary>

        /// <param name="sampleIDs"></param>

        /// <returns></returns>

        public DataTable GetBySampleIDs(List<string> sampleIDs)

        {

            using (BPDataContext dc = new BPDataContext(TCTC_ConnectionStrings.connStrJL))

            {

                var p = (from c in dc.TSampleOriginalInfo

                         where sampleIDs.Contains(c.FSampleID.ToString())

                         select new

                         {

                             c.FFromID,

                             c.FType,

                             c.FName,

                             c.FCode,

                             c.FRange,

                             c.FModel,

                             c.FUncertainty,

                             c.FCertificateNo,

                             c.FValidDateTo,

                             c.FManufacturer

                         }).Distinct();

                return LinqToDataTable.ToDataTable(p.ToList());

            }

        }

 

 

        /// <summary>

        /// 【join查询实例】获取带检测的器具信息

        /// </summary>

        /// <returns></returns>

        public DataTable GetBySampleName(string sampleName)

        {

            using (BPDataContext dc = new BPDataContext(TCTC_ConnectionStrings.connStrJL))

            {

                var sample = from c in dc.view_Sample_WithVCItem

                           where c.FEndTag == 1 && c.FTaskEndTag == 1 && c.FOutSourcingTag == 0 && c.FAssignTag == 1 && c.FTestCompleteTag == 0 && c.FIsOuter == "否" 

                           select c;

                var r = from s in sample

                        join v in dc.view_GetSampleLeastOrginalRecord

                        on s.FID equals v.FSampleID into recs

                        from v in recs.DefaultIfEmpty()

                        join t in dc.TTask

                        on s.FTaskID equals t.FID into ts

                        from t in ts

                        where (sampleName == "" ? true : s.FName == sampleName) && (s.FReceiverID == UserContext.CurrentUser.FID || TCTC_ConnectionStrings.TestResultFilterByTester == "0")

                        orderby s.FName, t.FCode, s.FCode

                        select new

                        {

                            SampleID = s.FID,

                            SampleCode = s.FCode,

                            s.FName,

                            s.FAnotherName,

                            s.FTaskID,

                            s.FIsRepair,

                            s.FIsNeedOriginalRecord,

                            s.FTestProperty,

                            s.FRepairTag,

                            s.VCItemID,

                            s.CertiID,

                            s.CertiName,

                            s.TechID,

                            s.TechName,

                            s.TechCode,

                            s.FReTestTag,

                            s.FReTestFromTag,       

                            v.FNumber,

                            v.FFileName,

                            v.FCertificateNo,

                            v.FOriginalRecordID,

                            v.FTag,

                            TaskCode = t.FCode,

                            t.FRemark,

                            t.FIsUrgent,

                            s.FTaskType,

                            s.FTaskTypeID,

                            s.FMeasurementRange,

                            s.FLevel,

                            s.FSigPrice

                        };

                DataTable dt = LinqToDataTable.ToDataTable(r.ToList());

                return dt;

            }

        }