将数据表内容加载到字典

Question

public static Dictionary<string, object> LonView()
        {
            string sql = "SELECT Marks,Id FROM table4";
            using (SqlConnection Connection = new SqlConnection((@"DataSource")))
            {
                using (SqlCommand myCommand = new SqlCommand(sql, Connection))
                {
                    Connection.Open();
                    using (SqlDataReader myReader = myCommand.ExecuteReader())
                    {
                        DataTable dt = new DataTable();
                        dt.Load(myReader);
                        Connection.Close();
  Dictionary<string, object> lst = new Dictionary<string, object>();
                      var tableEnumerable = dt.AsEnumerable();
                        var tableArray = tableEnumerable.ToArray();
                foreach (var data in tableArray)
                        {
                      lst.Add(data["id"].ToString(),data["Marks"] as string);
                        }

return lst;
          }
      }
   }
}

我想将我的数据表列转换为字典并以数组{["A",30],["B",32],["C",45]} 形式返回字典。建议一些想法做我的任务。

Answer 1

看看这个例子：

        DataTable table = new DataTable();
        table.Columns.Add("Id", typeof(string));
        table.Columns.Add("Marks", typeof(int));
        table.Rows.Add(new object[] { "A", 50 });
        table.Rows.Add(new object[] { "B", 100 });
        table.Rows.Add(new object[] { "C", 200 });

        Dictionary<string, int> dict = new Dictionary<string, int>();
        foreach (DataRow row in table.Rows)
        {
            dict.Add(row[0].ToString(), Convert.ToInt32(row[1].ToString()));
        }

        var arr = dict.ToArray();

这对你有帮助吗？

确保您的查询不会返回重复的 ID 值（字典中的键），因为您会遇到异常。

Answer 2

试试这个例子

dt.AsEnumerable()
      .ToDictionary<DataRow, string, object>(row => row.Field<string>(0),
                                row => row.Field<object>(1));

这会对你有所帮助。

Answer 3

你不必创建任何DataTable，临时Dictionary：一个简单的直接while循环就可以了

 string sql = 
   @"SELECT Marks,
            Id 
       FROM table4";

 using (SqlConnection Connection = new SqlConnection((@"DataSource"))) {
   using (SqlCommand myCommand = new SqlCommand(sql, Connection)) {
     Connection.Open();

     // We don't know the final array's length; let's use a list as a buffer  
     List<string[]> buffer = new List<string[]>();

     using (SqlDataReader myReader = myCommand.ExecuteReader()) {
       while (myReader.Read())
         buffer.Add(new string[] {
           Convert.ToString(myReader["id"]),
           Convert.ToString(myReader["Marks"]),
         });
     } 

     return buffer.ToArray(); 
   }         
 }

编辑：如果您出于某种目的想保留DataTable

 using (SqlConnection Connection = new SqlConnection((@"DataSource"))) {
   using (SqlCommand myCommand = new SqlCommand(sql, Connection)) {
     Connection.Open();

     using (SqlDataReader myReader = myCommand.ExecuteReader()) {
       DataTable dt = new DataTable();
       dt.Load(myReader);

       // You can obtain the string[][] array via Linq: 
       string[][] result = dt
         .AsEnumerable()
         .Select(record => new string[] {
            Convert.ToString(record["id"]),
            Convert.ToString(record["Marks"]), })
         .ToArray();

       ...
     }
     ... 

Answer 4

非常简单的请求：

        public static Dictionary<string, object> LonView()
        {
            string sql = "SELECT Marks,Id FROM table4";
            Dictionary<string, object> lst = null;
            using (SqlConnection Connection = new SqlConnection((@"DataSource")))
            {
                using (SqlDataAdapter adapter = new SqlDataAdapter(sql, Connection))
                {
                    DataTable dt = new DataTable();
                    adapter.Fill(dt);
                    Connection.Close();
                    lst = dt.AsEnumerable()
                        .GroupBy(x => x.Field<string>("Marks"), y => y.Field<object>("Id"))
                        .ToDictionary(x => x.Key, y => y.FirstOrDefault());
                }
            }
            return lst;

         }

---

如果数据库中的值为日期时间

        public static Dictionary<string, DateTime> LonView()
        {
            string sql = "SELECT Marks,Id FROM table4";
            Dictionary<string, DateTime> lst = null;
            using (SqlConnection Connection = new SqlConnection((@"DataSource")))
            {
                using (SqlDataAdapter adapter = new SqlDataAdapter(sql, Connection))
                {
                    DataTable dt = new DataTable();
                    adapter.Fill(dt);
                    Connection.Close();
                    lst = dt.AsEnumerable()
                        .GroupBy(x => x.Field<string>("Marks"), y => y.Field<DateTime>("Id"))
                        .ToDictionary(x => x.Key, y => y.FirstOrDefault());
                }
            }
            return lst;

        }