问题是delete语句影响了意外的行数（0）。 自加载实体以来，实体可能已被删除

Question

问题是delete语句影响了意外的行数（0）。 自加载实体以来，实体可能已被删除。

using Delete_E.DAL;
using System.Data.Entity;
namespace Delete_E
{
    public partial class Form1 : Form
    {
        UserinfoEntities conn = new UserinfoEntities();
        tableUserinfo otable = new tableUserinfo();

        public Form1()
        {
            InitializeComponent();

        }

        private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            //otable.id = Convert.ToInt32(dgvData.CurrentRow.Cells["id"].Value.ToString());
            otable.Name = dgvData.CurrentRow.Cells[1].Value.ToString();
            otable.Email = dgvData.CurrentRow.Cells[2].Value.ToString();
            otable.Salary= Convert.ToDouble(dgvData.CurrentRow.Cells[3].Value.ToString());
            otable.Gender = dgvData.CurrentRow.Cells[4].Value.ToString();
            otable.Speciality = dgvData.CurrentRow.Cells[5].Value.ToString();
        }
        public void selectTable()
        {
            dgvData.DataSource=conn.tableUserinfoes.ToList<tableUserinfo>();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            selectTable();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            DialogResult qustion = MessageBox.Show("Are you Sure to Deleted this Record ","Message Deleted",MessageBoxButtons.YesNo,MessageBoxIcon.Information);

            if (qustion == DialogResult.Yes)
                if (conn.Entry(otable).State == EntityState.Detached)
                    MessageBox.Show("the sata is :"+ conn.Entry(otable).State);
            conn.tableUserinfoes.Attach(otable);
            conn.tableUserinfoes.Remove(otable);
            conn.SaveChanges();
            selectTable();
        }
    }
}

Answer 1

您的问题之一是在按钮单击事件中，
无论DialogResult如何， selectTable始终执行attach ， remove和selectTable 。

我想你的意思是

private void button1_Click(object sender, EventArgs e)
{
    DialogResult qustion = MessageBox.Show("Are you Sure to Deleted this Record ","Message Deleted",MessageBoxButtons.YesNo,MessageBoxIcon.Information);

    if (qustion == DialogResult.Yes)
    {
        if (conn.Entry(otable).State == EntityState.Detached)
            MessageBox.Show("the sata is :"+ conn.Entry(otable).State);
        conn.tableUserinfoes.Attach(otable);
        conn.tableUserinfoes.Remove(otable);
        conn.SaveChanges();
        selectTable();
    }
}

我不知道您为什么显示该消息，
以及为什么要先移除，然后再移除。
但是无论如何，如果没有{}，它将永远无法按预期工作。

Answer 2

您正在尝试删除不是来自实体接口的对象。 您需要直接从实体（例如，使用查询）实例化此tableUserinfo对象，或者至少使用ID（主键）创建它。

请检查以下代码：

public partial class Form1 : Form
{
    UserinfoEntities conn = new UserinfoEntities();
    int selectedUserInfoID; // Keep the currently selected ID of the tableUserinfo object

    public Form1()
    {
        InitializeComponent();
    }

    private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
    {
        // Save the clicked cell's ID (assuming it comes from this expression)
        selectedUserInfoID = Convert.ToInt32(dgvData.CurrentRow.Cells["id"].Value.ToString()); 
    }
    public void selectTable()
    {
        dgvData.DataSource=conn.tableUserinfoes.ToList<tableUserinfo>();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        selectTable();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        DialogResult qustion = MessageBox.Show("Are you Sure to Deleted this Record ","Message Deleted",MessageBoxButtons.YesNo,MessageBoxIcon.Information);

        if (qustion == DialogResult.Yes)
        {
             // Ask Entity to generate the proper object with the selected ID (has to be PRIMARY KEY in that table)
            tableUserinfo selectedUserInfo = conn.tableUserinfoes.Find(selectedUserInfoID);

            if (selectedUserInfo != null)
                conn.tableUserinfoes.Remove(selectedUserInfo); // Tell Entity to delete that object (row from database)

            conn.SaveChanges(); // Commit the delete operation
            selectTable();
        }
    }
}

创建具有正确ID的对象的另一种选择：

if (qustion == DialogResult.Yes)
{
    tableUserinfo otable = new tableUserinfo{ id = selectedUserInfoID };

    conn.tableUserinfoes.Attach(otable);
    conn.tableUserinfoes.Remove(otable);
    conn.SaveChanges();
    selectTable();
}