如何将数据从 sql 查询加载到 datagridview？

Question

我已经声明了 2 个字符串变量：

string fname;
string lname;

当我在 phpMyAdmin 数据库中编写 MySQL 查询时：

SELECT workers.FNAME, workers.LNAME FROM project1.workers INNER JOIN
project1.order_status ON workers.ID_WORKER = order_status.ID_WORKER 
INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER 
WHERE orders.ORDER_NUMBER = 'TEST' GROUP BY workers.FNAME, workers.LNAME

我有 2 个唤醒者：

-“亚当盖克斯”和

“安德鲁蠕虫”

然后我想存储这个查询中的对象并将该数据加载到 datagridview：

    string query1 = string.Format("SELECT workers.FNAME, workers.LNAME FROM project1.workers INNER JOIN project1.order_status " +
    "ON workers.ID_WORKER = order_status.ID_WORKER INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER " +
    "WHERE orders.ORDER_NUMBER = '"+ NrOrder +"' GROUP BY workers.FNAME, workers.LNAME");

    SQLdata.connection.Open();
    using (var command = new MySqlCommand(query1, SQLdata.connection))
    {
        using (var reader1 = command.ExecuteReader())
        {
            while (reader1.Read())
            {
                fname = Convert.ToString(reader1[0]);
                lname = Convert.ToString(reader1[1]);
            }
        }
    }

我在 while 循环中的代码行中设置了断点，并读取了所有 FNAME 和 LNAME。然后它正确加载所有数据。接下来我想将它们加载到datagridview。

        SQLdata.connection.Close();
        sick_leaves x = new sick_leaves();
        x.FNAME = fname;
        x.LNAME = lname;
        return x;     

并像这样绑定它们：

        sick_leaves a = calculate_sickness_leaves(txt_NrOrder.Text);

        cu = calculate_sickness_leaves(txt_NrOrder.Text);
        var source = new BindingSource();
        source.DataSource = cu;
        dataGridView2.DataSource = source;

然后使用 Orders.cs 文件中的数据：

public class sick_leaves
{
    public string FNAME { get; set; }
    public string LNAME { get; set; }
}

在 datagridview 中编译后，我只加载了 1 个 Worker：“Andrew Worm”。那应该是2个worker，所以它没有从sql查询中加载所有数据。

现在：如何将所有数据从 sql 查询加载到 datagridview？有任何想法吗？ 警告！我需要桌面应用程序方面的帮助

编辑

我想通过保存代码结构来加载该数据，因为我想通过计算疾病、离开时间来构建该 datagridview。 （带有TimeSpan 对象）。可以这样写吗？

我的代码：

GenerateOrder.cs：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using MySql.Data.MySqlClient;
using System.Windows.Forms.DataVisualization.Charting;
using iTextSharp.text;
using iTextSharp.text.pdf;
using System.IO;
using System.Diagnostics;

namespace ControlDataBase
{
    public partial class GenerateChartsOfOrders : Form
    {
        string fname;
        string lname;
        sick_leaves cu = new sick_leaves();
        public GenerateChartsOfOrders()
        {
            InitializeComponent();
        }        

        public void loaddata2()
        {
            string connect = "datasource=localhost;port=3306;username=root;password=";

            MySqlConnection connection = new MySqlConnection(connect);
            connection.Open();

            sick_leaves a = calculate_sickness_leaves(txt_NrOrder.Text);

            cu = calculate_sickness_leaves(txt_NrOrder.Text);
            var source = new BindingSource();
            source.DataSource = cu;
            dataGridView2.DataSource = source;

            connection.Close();
        }

        private sick_leaves calculate_sickness_leaves(string NrOrder)
        {
            string query1 = string.Format("SELECT workers.FNAME, workers.LNAME FROM project1.workers INNER JOIN project1.order_status " +
            "ON workers.ID_WORKER = order_status.ID_WORKER INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER " +
            "WHERE orders.ORDER_NUMBER = '"+ NrOrder +"' GROUP BY workers.FNAME, workers.LNAME");

            SQLdata.connection.Open();
            using (var command = new MySqlCommand(query1, SQLdata.connection))
            {
                using (var reader1 = command.ExecuteReader())
                {
                    while (reader1.Read())
                    {
                        fname = Convert.ToString(reader1[0]);
                        lname = Convert.ToString(reader1[1]);
                    }
                }
            }

            SQLdata.connection.Close();
            sick_leaves x = new sick_leaves();
            x.FNAME = fname;
            x.LNAME = lname;
            return x;         
        }
    }
}

Orders.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

    namespace ControlDataBase
    {
        public class sick_leaves
        {
            public string FNAME { get; set; }
            public string LNAME { get; set; }
        }
    }

SQLData.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql;
using MySql.Data.MySqlClient;

namespace ControlDataBase
{
    class SQLdata
    {
        public static MySqlConnection connection = new MySqlConnection
        ("datasource=localhost;port=3306;username=root;password=");
    }
}

Answer 1

代码有几个问题：

1. 您已将fname 和lname 定义为表单字段。
2. 在calculate_sickness_leaves 中您在while(reader1.Read()) 中设置了这些字段的值
3. 最后从calculate_sickness_leaves返回一个sick_leaves对象。

所以基本上，fname 和 lname 将始终包含表格最后一行的名字和姓氏，因为 1 和 2。

您的 DataGridView 将始终显示一条记录，因为 3。

解决问题：

1. 删除不需要的 fname 和 lname。
2. 将calculate_sickness_leaves的输出类型更改为IEnumerable<sick_leaves>。
3. 在while循环中，当从数据读取器中读取字段值时，创建一个sick_leavesyield return的新实例。

旁注

• 始终使用参数化查询来防止 SQL 注入。
• 在处理连接等一次性对象时，请始终使用using 语句。
• 如果您对使用类型化实体对象感兴趣，那么您可能需要查看MySQL Connector 以获取Entity Framework。

示例

您可以找到很多关于将数据加载到DataTable 或使用DataReader 的示例。无论如何，我将在这里再分享两个示例，向您展示如何从 MySql 获取数据并转换为特定类型的列表。

在以下示例中，我假设您有一个这样的 Employee 类：

public class Employee
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

示例 1 - 使用 DataAdapter、DataTable 和 Select 扩展方法

public IEnumerable<Employee> GetEmployees()
{
    string connectionString = "CONNECTION STRING";
    string commandText = "COMMAND TEXT";
    DataTable table = new DataTable();
    using (var adapter = new MySqlDataAdapter(commandText , connectionString))
        adapter.Fill(table);
    return table.AsEnumerable().Select(x => new Employee()
    {
        FirstName = x.Field<string>("FirstName"),
        LastName = x.Field<string>("LastName")
    });
}

示例 2 - 使用 DataReader 和 yield return new Employee

public IEnumerable<Employee> GetEmployees()
{
    string connectionString = "CONNECTION STRING";
    string commandText = "COMMAND TEXT";
    using (var connection = new MySqlConnection(connectionString))
    {
        connection.Open();
        using (var command = new MySqlCommand(commandText, connection))
        {
            using (var reader = command.ExecuteReader())
            {
                while (reader.Read())
                {
                    yield return new Employee()
                    {
                        FirstName = reader.GetFieldValue<string>(0),
                        LastName = reader.GetFieldValue<string>(1)
                    };
                }
            }
        }
    }
}

您可以像这样使用上述任何一种方法：

bindingSource.DataSource = GetEmployees();
dataGridView.DataSource = bindingSource;

Answer 2

这可能会有所帮助

private void GetData(string selectCommand)
    {
        try
        {
            // Specify a connection string.  
            // Replace <SQL Server> with the SQL Server for your Northwind sample database.
            // Replace "Integrated Security=True" with user login information if necessary.
            String connectionString =
                "Data Source=<SQL Server>;Initial Catalog=Northwind;" +
                "Integrated Security=True";

            // Create a new data adapter based on the specified query.
            dataAdapter = new SqlDataAdapter(selectCommand, connectionString);

            // Create a command builder to generate SQL update, insert, and
            // delete commands based on selectCommand. 
            SqlCommandBuilder commandBuilder = new SqlCommandBuilder(dataAdapter);

            // Populate a new data table and bind it to the BindingSource.
            DataTable table = new DataTable
            {
                Locale = CultureInfo.InvariantCulture
            };
            dataAdapter.Fill(table);
            bindingSource1.DataSource = table;

            // Resize the DataGridView columns to fit the newly loaded content.
            dataGridView1.AutoResizeColumns(
                DataGridViewAutoSizeColumnsMode.AllCellsExceptHeader);
        }
        catch (SqlException)
        {
            MessageBox.Show("To run this example, replace the value of the " +
                "connectionString variable with a connection string that is " +
                "valid for your system.");
        }
    }

Answer 3

C# 数据访问层（本例中 DAl.cs 中只有 1 个 sub 的简化示例）：

Using System.Data.SqlClient;

Public Class DAL
{
    Public Static void GetQueryResults(String cmdText)
    {
        SqlConnection oConn = New SqlConnection();
        oConn.ConnectionString = MainW.MyConnection;  // get connection string
        SqlCommand cmd = New SqlCommand(cmdText, oConn);
        DataSet ds = New DataSet();
        SqlDataAdapter da = New SqlDataAdapter(cmd);

        Try
        {
            oConn.Open();
            da.Fill(ds);       // retrive data
            oConn.Close();
        }
        Catch (Exception ex)
        {
            SysErrScreen errform = New SysErrScreen();
            errform.ChybaText.Text = ex.Message + Constants.vbCrLf + Constants.vbCrLf + cmdText;
            errform.ShowDialog();
            oConn.Close();
        }

        Return ds;
    }
}

在 VB.NET 中相同：

Imports System.Data.SqlClient

Public Class DAL

Public Shared Function GetQueryResults(cmdText As String)
    Dim oConn As New SqlConnection
    oConn.ConnectionString = MainW.MyConnection  ' get connection string
    Dim cmd As New SqlCommand(cmdText, oConn)
    Dim ds As New DataSet()
    Dim da As New SqlDataAdapter(cmd)

    Try
        oConn.Open()
        da.Fill(ds)       ' retrive data
        oConn.Close()
    Catch ex As Exception
        Dim errform As New SysErrScreen
        errform.ChybaText.Text = ex.Message & vbCrLf & vbCrLf & cmdText
        errform.ShowDialog()
        oConn.Close()
    End Try

    Return ds
End Function

End Class

注意，我在别处 (MainW.MyConnection) 定义了一个 ConnectionString，您可以在其中为所有应用程序设置它。您通常会在启动期间从某些设置（文件、应用程序变量）中检索它。

那我就不好用了（C#）：

Private void FillDGV()
{
    String cmdText = "SELECT workers.FNAME, workers.LNAME FROM project1.workers INNER JOIN project1.order_status " + 
"ON workers.ID_WORKER = order_status.ID_WORKER INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER " + 
"WHERE orders.ORDER_NUMBER = '" + NrOrder + "' GROUP BY workers.FNAME, workers.LNAME\"; ";
        DataSet ds;
        ds = DAL.GetQueryResults(cmdText);
        DataTable dt;
        if (ds.Tables.Count > 0)
        {
            dt = ds.Tables(0);
            this.DataGridView1.DataSource = dt;   // fill DataGridView
        }
    }

VB.NET：

Private Sub FillDGV()
    Dim cmdText As String = "SELECT workers.FNAME, workers.LNAME FROM project1.workers INNER JOIN project1.order_status " +
        "ON workers.ID_WORKER = order_status.ID_WORKER INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER " +
        "WHERE orders.ORDER_NUMBER = '" & NrOrder & "' GROUP BY workers.FNAME, workers.LNAME""; "
    Dim ds As DataSet
    ds = DAL.GetQueryResults(cmdText)
    Dim dt As DataTable
    If ds.Tables.Count > 0 Then
        dt = ds.Tables(0)
        Me.DataGridView1.DataSource = dt    ' fill DataGridView
    End If
End Sub

注意，我使用DataTable 作为数据对象，介于DataSet 和DataGridView 之间。由于多种原因，养成使用它的习惯是件好事（除非使用其他更高级的方法）。一个主要问题是，如果DataSet 表恰好为空，它不会删除您的DataGridView GUI 定义的列。您还可以在 DataTable 和 DataGridView 上更高效、更可靠地执行客户端数据操作。

也可以考虑，如果他应该使用BindingSource，而不是DataTable。它的实现与 DataTable 非常相似，所以如果你让这个例子正常工作，你可以切换到BindingSource，如果你需要的话。

另一个考虑是使用参数查询。如果您（您的用户）在封闭的环境中操作您的桌面应用程序，那就没问题了。但是，对于暴露的应用程序，您可以肯定会受到一些 SQL 注入 攻击。

Answer 4

从 SQL 数据库下载数据并将其呈现在 DataGridView 中时，此代码适用于我：

            string connectionString;
            String sql = "";
            SqlConnection cnn;

            sql = "SELECT workers.FNAME, workers.LNAME FROM project1.workers INNER JOIN project1.order_status " +
            "ON workers.ID_WORKER = order_status.ID_WORKER INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER " +
            "WHERE orders.ORDER_NUMBER = '"+ NrOrder +"' GROUP BY workers.FNAME, workers.LNAME"";
            connectionString = @"datasource=localhost;port=3306;username=root;password=";
            cnn = new SqlConnection(connectionString);
            cnn.Open();
            SqlDataAdapter dataadapter = new SqlDataAdapter(sql, cnn);
            DataSet ds = new DataSet();
            dataadapter.Fill(ds, "workers");
            dataGridView1.DataSource = ds;
            dataGridView1.DataMember = "workers";
            cnn.Close();