如何在第二个网格视图中显示信息

Question

我使用 Nordwind DB

这是我的应用程序的外观：

我想从第一个网格视图中选择一行，并在第二个网格视图中显示来自这些客户的订单，我还想在第一个网格视图中过滤 1 列或更多列。

GridView1：

private void Form1_Load(object sender, EventArgs e)
{
    SqlConnection conn = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Northwind.mdf;Integrated Security=True");conn.Open();

    SqlCommand cmd = new SqlCommand("select * from Customers", conn);

    SqlDataReader rdr = cmd.ExecuteReader();

    List<Customer> Customers = new List<Customer>();

    while (rdr.Read())
    {
        Customer c = new Customer();
        c.CustomerID = (string)rdr["CustomerID"];
        c.CompanyName = (string)rdr["CompanyName"];
        c.ContactName = (string)rdr["ContactName"];
        c.City = (string)rdr["City"];
        c.Country = (string)rdr["Country"];
        c.Phone = (string)rdr["Phone"];
        Customers.Add(c);
    }

    dataGridView1.DataSource = Customers;
}

GridView2：

private void dataGridView2_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
    SqlConnection conn = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Northwind.mdf;Integrated Security=True"); 
    conn.Open();

    SqlCommand cmd = new SqlCommand("select * from Orders", conn);

    SqlDataReader rdr = cmd.ExecuteReader();

    List<Order> Orders = new List<Order>();

    while (rdr.Read())
    {
        Order o = new Order();
        o.OrderID = (int)rdr["OrderID"];
        o.OrderDate = (DateTime)rdr["OrderDate"];
        o.ShipName = (string)rdr["ShipName"];
        o.ShipCity = (string)rdr["ShipCity"];
        o.ShipCountry = (string)rdr["ShipCountry"];
        Orders.Add(o);
    }

    dataGridView2.DataSource = Orders;
}

选择整行：

        {
            Customer c = (Customer)dataGridView1.CurrentRow.DataBoundItem;
        }

我认为 GridView2 中的 SqlCommand 不好，我也认为我需要更新表单，但我不知道该怎么做。

谁能给我正确的代码，甚至可以解释一下哪个部分做什么？

提前感谢，如果您需要更多信息，请说出来。

Answer 1

不要在CellContentClick 中执行此操作，而是在SelectionChanged 事件处理程序中执行此操作。订单必须有一个CustomerID，您可以使用它在 WHERE 子句中进行过滤：

private void dataGridView1_SelectionChanged(object sender, EventArgs e)
{
    if (dataGridView1.CurrentRow?.DataBoundItem is Customer customer) {
        var orders = new List<Order>();

        using (var conn = new SqlConnection(STR_Connection))
        using (var cmd = new SqlCommand("select * from Orders where CustomerID=@cid", conn)) {
            cmd.Parameters.Add("@cid", SqlDbType.NChar, 5).Value = customer.CustomerID;

            conn.Open();
            using (SqlDataReader rdr = cmd.ExecuteReader()) {
                while (rdr.Read()) {
                    var o = new Order {
                        OrderID = (int)rdr["OrderID"],
                        CustomerID = (string)rdr["CustomerID"],
                        OrderDate = (DateTime)rdr["OrderDate"],
                        ShipName = (string)rdr["ShipName"],
                        ShipCity = (string)rdr["ShipCity"],
                        ShipCountry = (string)rdr["ShipCountry"]
                    };
                    orders.Add(o);
                }
            }
        }

        dataGridView2.DataSource = orders;
    } else {
        dataGridView2.DataSource = null;
    }
}

将参数作为命令参数传递并将其连接成 SQL 命令字符串非常重要。这可能导致 SQL 注入攻击（这里可能不会，但在一般情况下......）。它还提高了查询的性能，因为 SQL-Server 可以缓存执行计划，因为命令字符串不会因不同的客户而改变。

将连接、命令和阅读器放在 using 语句中，以自动处理它们。

---

文本框过滤的工作方式非常相似。在文本框的TextChanged 或Validated 或Leave 事件中重新加载客户：

private void txtFilter_TextChanged(object sender, EventArgs e)
{
    LoadCustomers(txtFilter.Text);
}

还有在 Load 事件中：

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

TextChanged 和其他两个事件的区别在于前者会为每个输入的字符触发。要让其他人工作，您必须离开文本框。

然后您将不得不处理过滤器是否为空的两种情况。如果为空，则选择没有 WHERE 子句的客户（即返回所有行）或根本不返回行（dataGridView1.DataSource = null;）。否则设置适当的 where 子句。也许

WHERE CompanyName LIKE @filter OR ContactName LIKE @filter

然后将过滤器字符串嵌入%。这是 SQL 中的通配符。

private void LoadCustomers(string filter = null) // Optional filter parameter
{
    string sql = "select * from Customers";
    SqlParameter filterParameter = null;
    if (!String.IsNullOrWhiteSpace(filter)) {
        sql += " WHERE CompanyName LIKE @filter OR ContactName LIKE @filter";
        filterParameter = new SqlParameter("@filter", SqlDbType.NVarChar) {
            Value = "%" + filter + "%" // Add wildcards.
        };
    }

    var Customers = new List<Customer>();
    using (var conn = new SqlConnection(STR_Connection))
    using (var cmd = new SqlCommand(sql, conn)) {
        if (filterParameter != null) {
            cmd.Parameters.Add(filterParameter);
        }
        conn.Open();
        using (var rdr = cmd.ExecuteReader()) {
            while (rdr.Read()) {
                var c = new Customer() {
                    CustomerID = (string)rdr["CustomerID"],
                    CompanyName = (string)rdr["CompanyName"],
                    ContactName = (string)rdr["ContactName"],
                    City = (string)rdr["City"],
                    Country = (string)rdr["Country"],
                    Phone = (string)rdr["Phone"]
                };
                Customers.Add(c);
            }
        }
    }
    dataGridView1.DataSource = Customers;
}