C# - 将 DataReader 转换为 DataTable

Posted 2023-05-07

【中文标题】C# - 将 DataReader 转换为 DataTable

【英文标题】：C# - Converting DataReader to DataTable

【发布时间】：2021-06-23 15:24:30

【问题描述】：

我想将 DataReader 转换为 DataTable 以显示数据库中的列表（demoClients）中的所有客户。

目前我有这个：

   using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Threading.Tasks;
    using mysqlConnector;
    using ProjectDatabase.Controllers;
    using System.Data;
    using System.Data.Common;
    namespace ProjectDatabase.Models
    
        public class demoClientsQuery
        
            public AppDb Db  get; 
    
            public demoClientsQuery(AppDb db)
            
                Db = db;
            
    
            public async Task<demoClients> FindAllClientsAsync(int id)
            
                using var cmd = Db.conDemo.CreateCommand();
                cmd.CommandText = @"Query";
                cmd.Parameters.Add(new MySqlParameter
                
                    ParameterName = "@id_customer",
                    DbType = DbType.Int32,
                    Value = id,
                );
                
                MySqlDataReader dataReader = cmd.ExecuteReader();
                DataTable dataTable = new DataTable();
                dataTable.Load(dataReader);
                var result = await ReadAllAsync(dataTable);            
                return result.Count > 0 ? result[0] : null;
            
    
    
            public async Task<List<demoClients>> LatestClientsAsync()
            
                using var cmd = Db.conDemo.CreateCommand();
                cmd.CommandText = @"Query";
    
                var aa = await LatestClientsAsync2();
                
                MySqlDataReader dataReader = cmd.ExecuteReader();
                DataTable dataTable = new DataTable();
                dataTable.Load(dataReader);            
                return await ReadAllAsync(dataTable);
            
    
            public async Task<DataTable> LatestClientsAsync2()
            
                using var cmd = Db.conDemo.CreateCommand();
                cmd.CommandText = @"Query";
    
    
                //return await ReadAllAsync(await cmd.ExecuteReaderAsync());
                return await ToDataTable(cmd);
            
    
            private async Task<DataTable> ToDataTable(MySqlCommand cmd)
            
    
    
                cmd.CommandType = CommandType.Text;
                using (DbDataAdapter dataAdapter = new MySqlDataAdapter(cmd))
                
                    cmd.CommandType = CommandType.Text;                               
                    DataTable data = new DataTable();                
                    dataAdapter.Fill(data);
                    
                    return data;
                
               
            
    
            private async Task<List<demoClients>> ReadAllAsync(DataTable dataTable)
            
                var adb_demo_clients = new List<demoClients>();
                using (dataTable)
                
                    
                    foreach (DataRow dr in dataTable.Rows)
                    
                        int id_customer = Convert.ToInt32(dr["id_customer"]);
                        string delivery_person_name = Convert.ToString(dr["delivery_person_name"]);
                        string firstname = Convert.ToString(dr["firstname"]);
                        string lastname = Convert.ToString(dr["lastname"]);
                        string email = Convert.ToString(dr["email"]);
                    
                    
                
                return adb_demo_clients;
            
       
        
    

我遇到的唯一问题是它什么都不返回，它返回空，我的代码中的某些东西没有从我的数据库中返回我的数据。

任何帮助将不胜感激。

感谢您的宝贵时间。

【问题讨论】：

doesn't return nothing - 所以它确实返回了一些东西

您的MySqlConnection 和您的connectionString 在哪里？你能连接到数据库吗？或者你在数据表中转换你的回报有问题吗？

直到DataTable 派生自IDisposable，您可以将其放入using 语句中

您知道您的方法ReadAllAsync 只读取数据表行但从不向列表中添加任何内容adb_demo_clients ？

foreach (DataRow dr in dataTable.Rows) demoClients d = new demoClients(); d.Id = Convert.ToInt32(dr["id_customer"]);; //fill all you fields that you need 所以在那之后你必须在你的列表中添加adb_demo_clients.add(d);（在你关闭你的foreach之前）

【参考方案1】：

您必须在 foreach 内的 ReadAllAsync 方法上将项目添加到 adb_demo_clients 列表中：

private async Task<List<demoClients>> ReadAllAsync(DataTable dataTable)

    var adb_demo_clients = new List<demoClients>();
    using (dataTable)
           
        foreach (DataRow dr in dataTable.Rows)
        
            demoClients d = new demoClients();

            d.id_customer = Convert.ToInt32(dr["id_customer"]);
            d.delivery_person_name = Convert.ToString(dr["delivery_person_name"]);

            // all fields that you need
            ...
            
            // Add the item in your List
            adb_demo_clients.add(d);
        
        
    
    return adb_demo_clients;