Question

可能重复：
Errors with codes for deleting using linq

我遇到了使用组合框删除数据的问题。错误提示我，我不知道如何解决它。任何人都可以帮助我吗？

private void btnDel_Click(object sender, EventArgs e)
    {
        using (testEntities Setupctx = new testEntities())
        {
            var Lo = Convert.ToInt16(cbLocationData.SelectedValue);
            var DeleteLocation = (from delLocation in Setupctx.locations
                                  where delLocation.Location1 == Lo
                                  select delLocation).Single();
            Setupctx.DeleteObject(DeleteLocation);
            Setupctx.SaveChanges();
            this.Delete_Location_Load(null, EventArgs.Empty);
            MessageBox.Show("Selected Shift Timing Has Been Deleted.");
        }
    }

部分where delLocation.Location1 == Lo向我显示错误

运算符'=='不能应用于'string'和'short'类型的操作数。“。

非常感谢您的帮助。

以上问题的答案如下：

 private void btnDel_Click(object sender, EventArgs e)
    {
        using (testEntities Setupctx = new testEntities())
        {
            string selectLo = cbLocationData.SelectedItem.ToString();

            var DeleteLocation = (from delLocation in Setupctx.locations
                                  where delLocation.Location1 == selectLo
                                  select delLocation).SingleOrDefault();
            if (DeleteLocation != null)
            {
                Setupctx.DeleteObject(DeleteLocation);
                Setupctx.SaveChanges();
                cbLocationData.SelectedIndex = -1;
                this.Delete_Location_Load(null, EventArgs.Empty);
                MessageBox.Show("Selected Shift Timing Has Been Deleted.");
            }
        }
    }

Answer 1

这意味着您无法比较 delLocation.Location1和Lo，因为它们具有不同的数据类型。尝试：

where delLocation.Location1.Equals(Lo.ToString())

Answer 2

显然Location1是string，无法使用short直接与==进行比较。不要将Lo转换为short，然后转换回string，请尝试：

var Lo = (string)cbLocationData.SelectedValue;

Answer 3

错误说您正在尝试将字符串与Int16进行比较。因为我们已经知道Lo是一个Int16，所以delLocation.Location1必须是字符串。因此，要解决此问题，请删除Convert.ToInt16()（因为下拉列表的SelectedValue为字符串），如下所示：

private void btnDel_Click(object sender, EventArgs e)
{
    using (testEntities Setupctx = new testEntities())
    {
        var Lo = Convert.ToString(cbLocationData.SelectedValue);
        var DeleteLocation = (from delLocation in Setupctx.locations
                              where delLocation.Location1 == Lo
                              select delLocation).Single();
        Setupctx.DeleteObject(DeleteLocation);
        Setupctx.SaveChanges();
        this.Delete_Location_Load(null, EventArgs.Empty);
        MessageBox.Show("Selected Shift Timing Has Been Deleted.");
    }
}

更新

如果您收到错误“序列不包含任何元素”，则表示您的查询未返回任何结果，并且您无法对空序列执行Single()。您可以使用SingleOrDefault()，然后检查值是否为null，如下所示：

private void btnDel_Click(object sender, EventArgs e)
{
    using (testEntities Setupctx = new testEntities())
    {
        var Lo = Convert.ToString(cbLocationData.SelectedValue);
        var DeleteLocation = (from delLocation in Setupctx.locations
                              where delLocation.Location1 == Lo
                              select delLocation).SingleOrDefault();
        if (DeleteLocation != null)
        {
            Setupctx.DeleteObject(DeleteLocation);
            Setupctx.SaveChanges();
            this.Delete_Location_Load(null, EventArgs.Empty);
            MessageBox.Show("Selected Shift Timing Has Been Deleted.");
        }
    }
}

使用linq删除代码时出错

3 个答案:

更新