一个关于多线程和DbHelper的问题

我的初衷是这样的：在多线程环境下，每个数据库编号对应一个DbHelper对象。

下面是代码，不知道这样写有什么问题。

 1 namespace TestDAL
 2 {
 3     public class DB
 4     {
 5         private static string[] ConnString = new[]
 6         {
 7             "unknown", "Data Source=163.163.1.100;Initial Catalog=xiaomi;User Id=sa;Password=1234567890;",
 8             "Data Source=163.163.1.101;Initial Catalog=xiaomi;User Id=sa;Password=1234567890;"
 9         };
10         private static readonly ConcurrentDictionary<int, DbHelperSQLP> concurentDictionary;
11         static DB()
12         {
13             concurentDictionary = new ConcurrentDictionary<int, DbHelperSQLP>();
14         }
15         private DB()
16         {
17         }
18         public static DbHelperSQLP GetDBHelper(int id)
19         {
20             if (!concurentDictionary.ContainsKey(id))
21                 concurentDictionary.TryAdd(id, new DbHelperSQLP(ConnString[id]));
22             DbHelperSQLP db;
23             bool result = concurentDictionary.TryGetValue(id, out db);
24             return result ? db : null;
25         }
26     }
27 }

调用方法是：

 1         /// <summary>
 2         /// 得到一个对象实体
 3         /// </summary>
 4         public xiaomi GetModel(int dbno, int id)
 5         {
 6             StringBuilder strSql = new StringBuilder();
 7             strSql.Append("select  top 1 id,username,password,email,ip from xiaomi ");
 8             strSql.Append(" where [email protected]");
 9             SqlParameter[] parameters = {
10                     new SqlParameter("@id", SqlDbType.Int,4)
11             };
12             parameters[0].Value = id;
13             DbHelperSQLP helper = DB.GetDBHelper(dbno);
14             if (helper == null)
15                 throw new SqlNullValueException("没有找到数据库地址");
16             DataSet ds = helper.Query(strSql.ToString(), parameters);
17             return ds.Tables[0].Rows.Count > 0 ? DataRowToModel(ds.Tables[0].Rows[0]) : null;
18         }