在C#VS2013中的System.Data.DataTable中将列定义为可为空

Question

我需要在C#VS2013中定义一个System.Data.DataTable.

在一列中,它可以是int或null.

但我得到了:

  DataSet does not support System.Nullable<>.

对于定义:

  public DataTable myDataTable
  myDataTable = new DataTable("myName");
  myDataTable.Columns.Add("ID", typeof(Int32)); 
  myDataTable.Columns.Add("value1", typeof(Int32?)); // run time error 
  myDataTable.Columns.Add("value2", typeof(Int32?)); 

有任何想法吗 ？解决？

使列Dullable后,

 DataColumn dc = myDataTable.Columns.Add("value1", typeof(Int32));
 dc.AllowDBNull = true;

当我查询它时,我得到了

  "Sequence contains no elements". 

请参阅更新.

UPDATE

    int? result = (from r in myDataTable.AsEnumerable()
                  where r.Field<Int32>("ID") == givenID
                    && r.Field<Int32?>("value1") == givenValue1
                    select r.Field<Int32>("value2")).First();

Answer 1

它是DataColumn的属性

public DataTable myDataTable
myDataTable = new DataTable("myName");
myDataTable.Columns.Add("ID", typeof(Int32)); 
DataColumn dc = myDataTable.Columns.Add("value1", typeof(Int32)); 
dc.AllowDBNull = true;

关于AllowDBNull的MSDN

Answer 2

尝试

  public DataTable myDataTable
  myDataTable = new DataTable("myName");
  myDataTable.Columns.Add("ID", typeof(Int32)); 
  myDataTable.Columns.Add(new DataColumn { ColumnName = "VALUE1", DataType = typeof(int), AllowDBNull = true });
  myDataTable.Columns.Add(new DataColumn { ColumnName = "VALUE2", DataType = typeof(int), AllowDBNull = true });

这将使值列可以为空

并在插入时

DataRow dr = myDataTable.NewRow();
dr["VALUE1"] = object.value1==null? (object)DBNull.Value : object.value1;

这将执行所需的操作