Question

我对LINQ有疑问我想要内连接两个DataTables，代码如下：

    DataTable dt1 = new DataTable();
    DataTable dt2 = new DataTable();

    dt1.Columns.Add("TEST1");
    dt1.Columns.Add("TEST2");
    dt1.Columns.Add("TEST3");
    dt1.Columns.Add("TEST4");

    dt2.Columns.Add("TEST2");
    dt2.Columns.Add("TEST5");
    dt2.Columns.Add("TEST6");
    dt2.Columns.Add("TEST7");

    for (int i = 0; i < 10; i++)
    {
        DataRow row = dt1.NewRow();
        row["TEST1"] = "aaa";
        row["TEST2"] = string.Format("bbb-{0}{1}{2}", i, (i % 2 == 0 ? "-" : ""), (i % 2 == 0 ? "ddd" : ""));
        row["TEST3"] = i.ToString();
        row["TEST4"] = "ddd";
        dt1.Rows.Add(row);
    }

    for (int i = 0; i < 8; i++)
    {
        DataRow row = dt2.NewRow();
        row["TEST2"] = "bbb";
        row["TEST5"] = i.ToString();
        row["TEST6"] = i % 2 == 0 ? "ddd" : "";
        row["TEST7"] = "sss";
        dt2.Rows.Add(row);
    }

dt1的描述是：

TEST1 TEST2     TEST3 TEST4
---------------------------
aaa bbb-0-ddd   0       ddd
aaa bbb-1       1       ddd
aaa bbb-2-ddd   2       ddd
aaa bbb-3       3       ddd
aaa bbb-4-ddd   4       ddd
aaa bbb-5       5       ddd
aaa bbb-6-ddd   6       ddd
aaa bbb-7       7       ddd
aaa bbb-8-ddd   8       ddd
aaa bbb-9       9       ddd

dt2的描述是：

  TEST1 TEST5     TEST6  TEST7  
  ----------------------------  
  bbb     0         ddd    sss    
  bbb     1                sss    
  bbb     2         ddd    sss    
  bbb     3                sss    
  bbb     4         ddd    sss    
  bbb     5                sss    
  bbb     6         ddd    sss    
  bbb     7                sss

第一个问题是，我想加入dt1和dt2作为

 TEST2     TEST3   TEST7
---------------------------
bbb-0-ddd   0       sss
bbb-1       1       sss
bbb-2-ddd   2       sss
bbb-3       3       sss
bbb-4-ddd   4       sss
bbb-5       5       sss
bbb-6-ddd   6       sss
bbb-7       7       sss

所以我把代码写成下面的状态，我想加入dt1和dt2到dt

    DataTable dt = new DataTable();
    dt.Columns.Add("TEST2");
    dt.Columns.Add("TEST3");
    dt.Columns.Add("TEST7");
    var result = from A1 in dt1.AsEnumerable()
                 join
                    A2 in dt2.AsEnumerable()
                 on
                    A1.Field<string>("TEST2") equals (A2.Field<string>("TEST2") + "-" + A2.Field<string>("TEST5") + (A2.Field<string>("TEST6") == string.Empty ? "-" : string.Empty) + A2.Field<string>("TEST6"))
                 select new dt.LoadDataRow(new object[] { A1.Field<string>("TEST2"), A1.Field<string>("TEST3"), A2.Field<string>("TEST7") }, false);
    result.CopyToDataTable();

但它不起作用〜此外，我想更改TEST3和TEST7的列，TEST3将命名为X1，TEST3将命名为X5，因此最新行的代码应为

选择新的dt.LoadDataRow（新对象[] {A1.Field（“TEST2”），X1 = A1.Field（“TEST3”），X5 = A2.Field（“TEST7”）}，false）; < / p>

这是另一个问题......我该怎么做????

Answer 1

而不是LoadDataRow + CopyToDataTable方法，我总是更喜欢简单的foreach，我在查询中添加这些行。这更清楚，不依赖于副作用。

您可以加入字符串并将两行放在匿名类型中：

var query = from r1 in dt1.AsEnumerable()
            join r2 in dt2.AsEnumerable()
            on r1.Field<string>("TEST2")
            equals string.Format("{0}-{1}-{2}"
                    , r2.Field<string>("TEST2")
                    , r2.Field<string>("TEST5")
                    , r2.Field<string>("TEST6"))
            select new { r1, r2 };

foreach (var bothRows in query)
{
    DataRow addedRow = dt.Rows.Add();
    addedRow.SetField("TEST2", bothRows.r1.Field<string>("TEST2"));
    addedRow.SetField("TEST3", bothRows.r2.Field<string>("TEST3"));
    addedRow.SetField("TEST7", bothRows.r2.Field<string>("TEST7"));
}

Answer 2

在互联网上，您可以找到一个非常有用的功能，名为LinqToDataTable（附在下面），您可以将任何查询LINQ转换为DataTable，保留查询产生的数据类型。

 public DataTable LINQToDataTable<T>(IEnumerable<T> varlist)
        {
            DataTable dtReturn = new DataTable();
            PropertyInfo[] oProps = null;

            if (varlist == null) return dtReturn;

            foreach (T rec in varlist)
            {
                // Use reflection to get property names, to create table, Only first time, others will follow 
                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;
        }

应该轻松调用该函数：

var result = (from A1 in dt1.AsEnumerable()
                          join
                             A2 in dt2.AsEnumerable()
                          on
                             A1.Field<string>("TEST2") equals (A2.Field<string>("TEST2") + "-" + A2.Field<string>("TEST5") + (A2.Field<string>("TEST6") == string.Empty ? "-" : string.Empty) + A2.Field<string>("TEST6"))
                          select new { 
                                TEST2 = A1.Field<string>("TEST2"), 
                                x1 = A1.Field<string>("TEST3"), 
                                x2 = A2.Field<string>("TEST7")
                          });

            DataTable dtFinal = LINQToDataTable(result);

通过LINQ从DataTable到DataTable的多个on子句

2 个答案: