Question

我在这里没什么问题。我尝试使用SqlDataReader从数据库中读取数据。代码是这样的：

        internal static User GetUser(string login)
    {
        SqlConnection conn = new SqlConnection(DataBaseUtility.ConnectionString);

        conn.Open();

        string sql = "SELECT * FROM BookMenagerDB.dbo.users";
        //where UserLogin like @login
        try
        {
            SqlCommand cmd = new SqlCommand(sql, conn);
            cmd.Parameters.AddWithValue("@login", login);
            User user = new User();
            SqlDataReader sqlDataReader = cmd.ExecuteReader();
            user.Id = (int)sqlDataReader["UserId"];
            user.Login = sqlDataReader["UserLogin"].ToString();
            user.PasswordHash = sqlDataReader["UserPassword"].ToString();
            user.Salt = (byte[])sqlDataReader["UserPasswordSalt"];
            return user;
        }

        catch (SqlException ex)
        {
            MessageBox.Show("GetUser fail");
        }
        conn.Close();
        return new User();
    }

我尝试执行sql查询，但获取了数据，但行“ user.Id =（int）sqlDataReader [“ UserId”];“告诉我sqlDataReader中没有数据。我不知道是什么问题。

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Answer 1

您需要在SqlDataReader上调用Read()函数，以将读取器前进到数据库中的第一条记录或下一条记录。另外，您应该使用处置释放连接和资源。

public User GetUser(string login)
{
    User user = new User();
    const string sql = "SELECT * FROM BookMenagerDB.dbo.users";
    using (SqlConnection connection = new SqlConnection(DataBaseUtility.ConnectionString))
    using (SqlCommand command = new SqlCommand(sql, connection))
    {
        connection.Open();
        command.Parameters.AddWithValue("@login", login);
        using (SqlDataReader reader = command.ExecuteReader())
        {
            if (reader.Read())
            {
                user.Id = (int)reader["UserId"];
                user.Login = reader["UserLogin"].ToString();
                user.PasswordHash = reader["UserPassword"].ToString();
                user.Salt = (byte[])reader["UserPasswordSalt"];
            }
        }
    }
    return user;
}

Answer 2

在ExecuteReader()之后，您应该Read()来获取记录：

   User user = new User();
   SqlDataReader sqlDataReader = cmd.ExecuteReader();
   if(sqlDataReader.Read())
   {
       user.Id = (int)sqlDataReader["UserId"];
       user.Login = sqlDataReader["UserLogin"].ToString();
       user.PasswordHash = sqlDataReader["UserPassword"].ToString();
       user.Salt = (byte[])sqlDataReader["UserPasswordSalt"];
    }

C＃sqldatareader没有数据

2 个答案: