Question

 VotingDemoDataContext db = new VotingDemoDataContext();
        var x = (from name in db.Elections select name);
        int n = x.Count();

        Election election = new Election();
        election.ElectionID = n.ToString();
        Constituency c=new Constituency();
        election.ConstituencyId = Convert.ToInt32(from m in db.Elections where (c.ConstituencyName==ddlConstitency.SelectedItem.Text) select m.ConstituencyId);
        election.Date = Convert.ToDateTime(txtDate.Text);
        election.ElectionType = ddlEType.SelectedItem.Text;
        election.EO = txtEOName.Text;
        election.EOPassword = txtEOPassword.Text;

        db.Elections.InsertOnSubmit(election);
        db.SubmitChanges();

        txtEOPassword.Text = "";
        txtDate.Text = "";
        txtResultDate.Text = "";
        ddlConstitency.SelectedIndex = 0;
        ddlEType.SelectedIndex = 0;
        txtEOName.Text = "";

此代码返回行的唯一空例外：election.ConstituencyId = Convert.ToInt32(from m in db.Elections where (c.ConstituencyName==ddlConstitency.SelectedItem.Text) select m.ConstituencyId);

Answer 1

  where (c.ConstituencyName==ddlConstitency.SelectedItem.Text)

我敢打赌问题就在这里......你的下拉列表中可能有一个选定的值，但是你刚刚创建了该选区对象......而且我没有看到随后为该ConstituencyName设置的任何属性创建对象。因此，您将下拉列表中的有效值与某些默认的ConstituencyName或null进行比较。由于没有匹配，查询将失败 - 等于评估将始终失败。

其中Asp.net中的子句在下面的代码中返回null异常

1 个答案: