LINQ的加入2个数据表，在新的DataTable

Question

我有以下数据表

表1共用列，并把结果：

+-----------+------+------+ 
| catalogid | name | snum | 
+-----------+------+------+ 
|  353 | xx | 4 | 
|  364 | yy | 3 | 
|  882 | zz | 3 | 
|  224 | mm | 71 | 
|  999 | kk | 321 | 
|  74 | kk | 4 | 
|  54 | ii | 5 | 
|  11 | u | 6 | 
|  23 | yy | 6 | 
+-----------+------+------+ 

表2：

+-----------+----------+--------------+ 
| catalogid | numitems | ignoreditems | 
+-----------+----------+--------------+ 
|  353 |  4 |   0 | 
|  364 |  10 |   0 | 
|  882 |  2 |   0 | 
|  224 |  0 |   7 | 
+-----------+----------+--------------+ 

使用LINQ我想加入它们并将结果复制到新的数据表中。他们都共享catalogid，并在结果应该只显示在表2

存在其采用catalogId

结果记录：

+-----------+------+------+-----------+---------------+ 
| catalogid | name | snum | numitems | ignoreditems | 
+-----------+------+------+-----------+---------------+ 
|  353 | xx | 4 |   4 |    0 | 
|  364 | yy | 3 |  10 |    0 | 
|  882 | zz | 3 |   2 |    0 | 
|  224 | mm | 71 |   0 |    7 | 
+-----------+------+------+-----------+---------------+ 

这里是我的尝试，但它不工作：

Dim query = From a In oresult.AsEnumerable 
      Group Join b In products.AsEnumerable 
      On a.Field(Of Integer)("catalogid") Equals b.Field(Of Integer)("catalogid") 
      Into Group 
query.copytodatatable 

CopyToDatatable不工作，我不知道为什么

Answer 1

CopyToDataTable（）仅当您的查询返回IEnumerable <'DataRow>时才起作用。在你的查询中，你正在返回一个匿名类型。匿名类型不包含CopyToDataTable（）的扩展方法。

您可以使用下面列出的ConvertToDataTable扩展名创建表。你必须将其转换为VB.NET（如果你是谷歌，那里有转换器）。

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Data; 
using Common; 

namespace TestConsole 
{ 
    public class Linq_join_2_datatables_that_share_a_column_and_put_result_in_new_datatable 
    { 
     public class Table1 
     { 
      public int CatalogId { get; set; } 
      public string Name { get; set; } 
      public int SNum { get; set; } 
     } 

     public class Table2 
     { 
      public int CatalogId { get; set; } 
      public int NumItems { get; set; } 
      public int IgnoredItems { get; set; } 
     } 

     public static void Start() 
     { 
      DataTable table1 = new DataTable(); 
      table1.Columns.Add("catalogid", typeof(int)); 
      table1.Columns.Add("name", typeof(string)); 
      table1.Columns.Add("snum", typeof(int)); 
      DataRow row = table1.Rows.Add(353, "xx", 4); 

      DataTable table2 = new DataTable(); 
      table2.Columns.Add("catalogid", typeof(int)); 
      table2.Columns.Add("numitems", typeof(int)); 
      table2.Columns.Add("ignoreditems", typeof(int)); 
      table2.Rows.Add(353, 4, 0); 

      var query = (from t1 in table1.AsEnumerable() 
         join t2 in table2.AsEnumerable() on t1.Field<int>("catalogid") equals t2.Field<int>("catalogid") 
         select new 
         { 
          catalogid = t1.Field<int>("catalogid"), 
          name = t1.Field<string>("name"), 
          snum = t1.Field<int>("snum"), 
          numitems = t2.Field<int>("numitems"), 
          ignoreditems = t2.Field<int>("ignoreditems") 
         }).ToList(); 

      DataTable table3 = query.ConvertToDataTable();  
     } 
    }  
} 

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Data; 
using System.ComponentModel; 
using System.Reflection; 

namespace Common 
{ 
    public static class DataTableExtensions 
    { 
     public static DataTable ConvertToDataTable<T>(this IList<T> data) 
     { 
      PropertyDescriptorCollection properties = 
       TypeDescriptor.GetProperties(typeof(T)); 
      DataTable table = new DataTable(); 
      foreach (PropertyDescriptor prop in properties) 
       table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType); 
      foreach (T item in data) 
      { 
       DataRow row = table.NewRow(); 
       foreach (PropertyDescriptor prop in properties) 
        row[prop.Name] = prop.GetValue(item) ?? DBNull.Value; 
       table.Rows.Add(row); 
      } 
      table.AcceptChanges(); 
      return table; 
     } 

    } 
} 

Answer 2

CopyToDataRow只适用于DataRow的IEnumerable s。对于任意IEnumerable s，请参阅this article at MSDN以获取CopyToDataRow的实现。