为什么数据表中的自动递增列变为空？

Question

我在数据表中创建了一个身份列 id，其自动递增等于 true，但它是空的。

为什么？

        Datatable dt= new datatable();

        DataColumn dc = new DataColumn("id", typeof(int));

        dc.AutoIncrement = true;
        dc.AutoIncrementSeed = 1;
        dc.AutoIncrementStep = 1;
        dt.Columns.Add(dc);

        dc = new DataColumn("NITNo", typeof(string));
        dc.DefaultValue = txtNitNo.Text.ToString();
        dt.Columns.Add(dc);

        dc = new DataColumn("WorkNo", typeof(string));
        dc.DefaultValue = txtWorkNo.Text.ToString();
        dt.Columns.Add(dc);
        //dt.Rows.rem

        //Bind Data to GridView
        gvBOQ.Caption = Path.GetFileName(FilePath);
        gvBOQ.DataSource = dt;
        gvBOQ.DataBind();

Answer 1

如果向DataTable添加数据，则必须确保Identity Column中的值为null

//create a datatable
DataTable table = new DataTable();

//auto increment column
DataColumn column = new DataColumn("id", typeof(int));
column.AutoIncrement = true;
column.AutoIncrementSeed = 1;
column.AutoIncrementStep = 1;
table.Columns.Add(column);

//add a normal column
column = new DataColumn("value", typeof(string));
table.Columns.Add(column);

//add some data to the table
table.Rows.Add(null, "Netherlands");
table.Rows.Add(null, "Japan");
table.Rows.Add(99, "Australia");
table.Rows.Add(null, "America");

生成的表格将如下所示

id  value
1   Netherlands
2   Japan
99  Australia
100 America