c# - 从数据库创建 TreeView

Question

我有一个名为 dtEmploye 的数据库，其中包含字段

employe_id
name
surname
boss_id which has a recursive relation on employee_id where I have in code XXX

我有代码，但有一些错误显示“指定的转换无效。”

private void btntree_Click(object sender, EventArgs e)
    {
        DataTable vec = sel("SELECT * FROM dtemployee");
        treeView1.Nodes.Clear();
        foreach (DataRow dr in vec.Rows)
        {
            if ((int)dr["boss_id"] == XXX)
            {
                TreeNode parent = new TreeNode();
                parent.Text = dr["name"+"surname"].ToString();
                string value = dr["employe_id"].ToString();
                parent.Expand();
                treeView1.Nodes.Add(parent);
                sublevel(parent, value);
            }
        }
    }
    public int sublevel(TreeNode parent, string id)
    {
        DataTable ch = sel("SELECT * FROM dtEmploye WHERE boss_id=" + id);
        if (dtEmploye.Rows.Count > 0)
        {
            foreach (DataRow dr in ch.Rows)
            {
                TreeNode child = new TreeNode();
                child.Text = dr["name"+"surname"].ToString().Trim();
                string temp = dr["employe_id"].ToString();
                child.Collapse();
                parent.Nodes.Add(child);
                sublevel(child, temp);
            }
            return 0;
        }
        else
        {
            return 0;
        }
    }
    protected DataTable sel(string select)
    {
        NpgsqlDataAdapter adpt = new NpgsqlDataAdapter(select, con);
        DataTable dt2 = new DataTable();
        adpt.Fill(dt2);
        return dt2;
    }

Answer 1

试试这个

    if ((int)dr["boss_id"] == XXX && DBNull.Value != dr["boss_id"])
    {
        TreeNode parent = new TreeNode();
        parent.Text = dr["name"].ToString() + dr["surname"].ToString();
        string value = dr["employe_id"].ToString();
        parent.Expand();
        treeView1.Nodes.Add(parent);
        sublevel(parent, value);
    }