在C#中如何连接数据库并循环遍历记录集？

Question

如何在C#中连接和查询数据库以获取一组记录？

- Michael Pryor

Answer 1

@Goyuix -- 这个记忆中写下来的东西非常棒。我在这里测试了一下，发现连接没有打开。除此之外非常好。

using System.Data.OleDb;
...

using (OleDbConnection conn = new OleDbConnection())
{
    conn.ConnectionString = "Provider=sqloledb;Data Source=yourServername\\yourInstance;Initial Catalog=databaseName;Integrated Security=SSPI;";

    using (OleDbCommand cmd = new OleDbCommand())
    {
        conn.Open();
        cmd.Connection = conn;
        cmd.CommandText = "Select * from yourTable";

        using (OleDbDataReader dr = cmd.ExecuteReader())
        {
            while (dr.Read())
            {
                Console.WriteLine(dr["columnName"]);
            }
        }
    }
}

- Leon Bambrick

Answer 2

因为我这台笔记本上没有代码，所以非常粗略地从记忆中描述：

using (OleDBConnection conn = new OleDbConnection())
{
  conn.ConnectionString = "Whatever connection string";

  using (OleDbCommand cmd = new OleDbCommand())
  {
    cmd.Connection = conn;
    cmd.CommandText = "Select * from CoolTable";

    using (OleDbDataReader dr = cmd.ExecuteReader())
    {
      while (dr.Read())
      {
        // do something like Console.WriteLine(dr["column name"] as String);
      }
    }
  }
}

- Goyuix

Answer 3

那绝对是一种好的做法。但是如果你正在使用支持LINQ to SQL的数据库，它会更加有趣。代码可能看起来像这样：

MyDB db = new MyDB("Data Source=...");
var q = from db.MyTable
        select c;
foreach (var c in q)
  Console.WriteLine(c.MyField.ToString());

- MojoFilter

Answer 4

这是一种替代方式（DataReader比这种方式更快）:

string s = "";
SqlConnection conn = new SqlConnection("Server=192.168.1.1;Database=master;Connect Timeout=30;User ID=foobar;Password=raboof;");
SqlDataAdapter da = new SqlDataAdapter("SELECT TOP 5 name, dbid FROM sysdatabases", conn);
DataTable dt = new DataTable();

da.Fill(dt);

for (int i = 0; i < dt.Rows.Count; i++)
{
    s += dt.Rows[i]["name"].ToString() + " -- " + dt.Rows[i]["dbid"].ToString() + "\n";
}

MessageBox.Show(s);

- Marek Grzenkowicz

Answer 5

如果您打算读取大量列或记录，值得缓存序数并访问强类型方法，例如：

using (DbDataReader dr = cmd.ExecuteReader()) {
  if (dr.Read()) {
    int idxColumnName = dr.GetOrdinal("columnName");
    int idxSomethingElse = dr.GetOrdinal("somethingElse");

    do {
      Console.WriteLine(dr.GetString(idxColumnName));
      Console.WriteLine(dr.GetInt32(idxSomethingElse));
    } while (dr.Read());
  }
}

- damieng

Answer 6

如果您正在查询SQL Server数据库（版本7及以上），则应将OleDb类替换为System.Data.SqlClient命名空间中的相应类（SqlConnection，SqlCommand和SqlDataReader），因为这些类已经优化以与SQL Server一起使用。

另一个需要注意的是，您不应该选择所有列，因为如果您添加或删除此表中的列，则可能会导致意外的结果。

- Christian Hagelid

Answer 7

我想你可以尝试使用实体框架。

using (SchoolDBEntities ctx = new SchoolDBEntities())
{
     IList<Course> courseList = ctx.GetCoursesByStudentId(1).ToList<Course>();
     //do something with courselist here
}

- kril

Answer 8

加载库文件

using MySql.Data.MySqlClient;

这是连接：

public static MySqlConnection obtenerconexion()
{
    string server = "Server";
    string database = "Name_Database";
    string Uid = "User";
    string pwd = "Password";
    MySqlConnection conect = new MySqlConnection("server = " + server + ";" + "database =" + database + ";" + "Uid =" + Uid + ";" + "pwd=" + pwd + ";");

    try
    {
        conect.Open();
        return conect;
    }
    catch (Exception)
    {
        MessageBox.Show("Error. Ask the administrator", "An error has occurred while trying to connect to the system", MessageBoxButtons.OK, MessageBoxIcon.Error);
        return conect;
    }
}

- Josué Ayala