添加列表在 C# 中搜索子字符串

Question

我正在创建应用程序，但我有一个问题。

客户端在文本框中写入用户名，例如3个字母并在数据库中搜索（访问）并添加数据库。

示例：用户：Rui。 并在数据库中搜索所有名称用户“Rui”。

//libraries
using Microsoft.VisualStudio.OLE.Interop;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.OleDb;
using System.Diagnostics;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

private void textBox1_TextChanged(object sender, EventArgs e)
{
    OleDbConnection conexao = new OleDbConnection(string.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source= {0}\Teste.accdb", Path.GetDirectoryName(Assembly.GetEntryAssembly().Location)));
        
    List<string> Users = new List<string>();

    
    OleDbCommand STK = new OleDbCommand($"SELECT NºCliente, NomeUser, CodigoPostal, NIF", conexao);
    STK.CommandText = $" SELECT* FROM MyTable WHERE Str(Lista_Pokemon) like '*{textBox1.Text}*'";

    User.Clear();
    //this code is invention, probably is wrong

    for(int d=0; d<Stk.Count()-1; d++)
         User.Add(...);
}

如果你能帮助我，谢谢。这个项目是c#，net framework，数据库是Access 2010。目前我不创建类，但如果你需要告诉我，我需要创建。

Answer 1

您需要创建一个 DbReader 并移动到下一行直到结束：

OleDbCommand STK = new OleDbCommand($"SELECT NºCliente, NomeUser, CodigoPostal, NIF", conexao);
STK.CommandText = $" SELECT * FROM MyTable WHERE Str(Lista_Pokemon) like '%{textBox1.Text}%'";

Users.Clear();

var reader = STK.ExecuteReader();
while (reader.Read())
    Users.Add(reader["Lista_Pokemon"].ToString());

将用户输入线程化到查询文本中被认为是一种危险的做法，在安全性方面也不是不安全的。 带参数最好“按书”行事：

OleDbCommand STK = new OleDbCommand();
STK.Connection = conexao;
STK.CommandText = "SELECT * FROM tblCliente WHERE User like @userParameter";
STK.Parameters.AddWithValue("@userParameter", $"%{textBox1.Text}%")

Users.Clear();

var reader = STK.ExecuteReader();
while (reader.Read())
    Users.Add(reader["User"].ToString());

Answer 2

看下面的代码。

using 运算符在这里用于释放资源——这很重要！

var dataSource = Path.Combine(
    Path.GetDirectoryName(Assembly.GetEntryAssembly().Location),
    "Teste.accdb");

var builder = new OleDbConnectionStringBuilder();
builder.Provider = "Microsoft.ACE.OLEDB.12.0";
builder.DataSource = dataSource;

var connectionString = builder.ToString();
var sql = "SELECT ..."; // place your query here

using (var connection = new OleDbConnection(connectionString))
{
    connection.Open();

    using (var command = new OleDbCommand(sql, connection))
    using (var reader = command.ExecuteReader())
    {
        var users = new List<User>();

        while (reader.Read())
        {
            var user = new User();

            user.ClientNumber = (int)reader["NºCliente"];
            user.UserName = (string)reader["NomeUser"];
            user.CodigoPostal = (string)reader["CodigoPostal"];
            user.NIF = (string)reader["NIF"];

            users.Add(user);
        }
        // return users; // Return data from method
    }
}

该类用于存储用户数据。
将属性名称和类型更改为您需要的。

class User
{
    public int ClientNumber { get; set; }
    public string UserName { get; set; }
    public string CodigoPostal { get; set; }
    public string NIF { get; set; }
}

当然，在 sql 查询中使用参数，正如 @dovid 在他的示例中所示。

Answer 3

感谢Alexander Petrov 和dovid，为我的问题提供了解决方案。但我“找到”了解决方案并发送了。

OleDbConnection conexao = new OleDbConnection(string.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source= {0}\Teste.accdb", Path.GetDirectoryName(Assembly.GetEntryAssembly().Location)));

       OleDbCommand STK = new OleDbCommand("SELECT * FROM MyTable ORDER BY Id"); 
conexao.Open();
           comando.Connection = STK;

           var reader = comando.ExecuteReader();

var users = new List<User>();


while (reader.Read())
                   {
                       var user = new User();

                       user.ClientNumber = (reader["ClientNumber "]);
                       user.UserName= reader["UserName"];
                       user.CodigoPostal= reader["CodigoPostal"];
                       user.NIF= reader["NIF"];

                       users.Add(user);
                   }

class User
        {
            public string ClientNumber { get; set; }
            public string UserName { get; set; }
            public string CodigoPostal { get; set; }
            public string NIF { get; set; }
        }