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个炒锅：

-“亚当·加克斯”和

“安德鲁·沃尔姆”

然后，我想从该查询存储对象，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循环中使用了代码行中的断点，并读取了所有FNAME和LNAME。然后，它将正确加载所有数据。接下来，我要将它们加载到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，我仅加载了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来构建该datagridview，从而节省了时间。（带有TimeSpan对象）。有可能这样写吗？

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

代码中存在一些问题：

1. 您已将fname和定义lname为表单字段。
2. 在calculate_sickness_leaves您设置这些字段的值中while(reader1.Read())
3. 最后，sick_leaves从返回一个对象calculate_sickness_leaves。

所以基本上，fname和lname将始终包含名字和你的表的最后一排的最后一个名字，是因为：1和2。

DataGridView由于3，您将始终显示一条记录。

解决问题：

1. 删除fname，lname因为您不需要它们。
2. 将输出类型更改calculate_sickness_leaves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 的新实例将其返回。

边注

• 始终使用参数化查询来防止SQL注入。
• using在处理诸如连接之类的一次性物品时，请始终使用声明。
• 如果你有兴趣的工作类型与实体对象，那么你可能想看看MySQL连接的实体框架。

例

您可以找到许多有关将数据加载到中DataTable或使用的示例DataReader。无论如何，我将在这里分享另外两个示例，向您展示如何从MySql获取数据并将其转换为特定类型的列表。

在以下示例中，我假设您有一个Employee类似的类：

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并产生return新的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)
                    };
                }
            }
        }
    }
}

您可以使用上述两种方法之一：

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

Answer 2

当我从 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();