Sql DataReader 有行但 Returns 有空数据

Question

我正在对 sql 数据库中的 select 数据进行查询。它有行，但数据 raader.Read() 函数 returns false 并且行是空的，因为我在调试

中检查过

我一直在使用的代码是

public void getSale()
    {
        DB db = new DB();

        try
        {
            db.cmd.CommandText = "select * from Sale where date is not null and (date between '"+StartDate+"' and '"+EndDate+"') order by date";
            db.cmd.Connection = db.con;
            db.con.Open();

            if(db.con.State == System.Data.ConnectionState.Open)
            {
                db.dataReader = db.cmd.ExecuteReader();

                if(db.dataReader.HasRows)
                {
                    while(db.dataReader.Read())
                    {
                        SaleModel sm = new SaleModel();
                        sm.SaleId = long.Parse(db.dataReader["Id"].ToString());
                        sm.UserName = db.dataReader["UserName"].ToString();
                        sm.ItemsQuantity = int.Parse(db.dataReader["ItemsQuantity"].ToString());
                        sm.TotalAmount = double.Parse(db.dataReader["TotalAmount"].ToString());
                        sm.SubTotal = double.Parse(db.dataReader["SubTotal"].ToString());
                        sm.Discount = double.Parse(db.dataReader["Discount"].ToString());
                        sm.Completed = bool.Parse(db.dataReader["Completed"].ToString());
                        sm.Date = DateTime.Parse(db.dataReader["Date"].ToString());
                        sm.CustomerPhone = long.Parse(db.dataReader["CustomerPhone"].ToString());

                        SalesList.Add(sm);
                    }

                    db.con.Close();
                }
            }
        }
        catch(Exception ex)
        {
            MessageBox.Show(ex.Message, "Exception", MessageBoxButton.OK, MessageBoxImage.Error, MessageBoxResult.OK);
        }
    }

当我在查询编辑器上测试此查询时，返回了 Visual studio 行

有没有人可以帮忙？

Answer 1

没有发现任何问题，只是您使用的是 date，这是一个保留字，而不是您的实际列名。将您的查询更改为

db.cmd.CommandText = "select * from Sale where [date] is not null and ([date] between '"+StartDate+"' and '"+EndDate+"') order by [date]";

Answer 2

为什么要连接字符串来构建 sql 查询？永远不要那样做。它是 sql-injection 的来源，可能会导致这样的问题。而是使用参数化查询。

也不要像 DB class 那样使用 SqlConnection 包装器。这可能会导致 several other issues。相反，最好使用 using-statament 在您需要的地方创建、打开、关闭和处置它们。连接池将为您管理其余部分。

public List<SaleModel> GetSale(DateTime startDate, DateTime endDate)
{
    string sql = @"select * from Sale 
                   where date is not null 
                   and date between @StartDate and @EndDate 
                   order by date";

    var salesList = new List<SaleModel>();

    try
    {
        using (var con = new SqlConnection("insert your connection string"))
        using (var cmd = new SqlCommand(sql, con))
        {
            cmd.Parameters.Add("@StartDate", SqlDbType.DateTime).Value = startDate;
            cmd.Parameters.Add("@EndDate", SqlDbType.DateTime).Value = endDate;
            con.Open();
            using (var reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    SaleModel sm = new SaleModel();
                    sm.SaleId = long.Parse(reader["Id"].ToString());
                    sm.UserName = reader["UserName"].ToString();
                    sm.ItemsQuantity = int.Parse(reader["ItemsQuantity"].ToString());
                    sm.TotalAmount = double.Parse(reader["TotalAmount"].ToString());
                    sm.SubTotal = double.Parse(reader["SubTotal"].ToString());
                    sm.Discount = double.Parse(reader["Discount"].ToString());
                    sm.Completed = bool.Parse(reader["Completed"].ToString());
                    sm.Date = DateTime.Parse(reader["Date"].ToString());
                    sm.CustomerPhone = long.Parse(reader["CustomerPhone"].ToString());

                    salesList.Add(sm);
                }
            }
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "Exception", MessageBoxButton.OK, MessageBoxImage.Error, MessageBoxResult.OK);
    }

    return salesList;
}

我很确定这行得通（f.e。可能是本地化问题）。

旁注：方法 GetSale 应该 return 一个 List<SaleModel> 而不是填充一个。您还应该将参数作为 DateTime 传递给该方法。我已经在我的代码示例中更改了它。

Answer 3

这是构建代码的好得多的方法，它很有可能也能解决您的问题：

//accept the date values as parameter arguments, return the result. 
//  Do NOT mess about with variables at the global or class scope.
public IEnumerable<SalesModel> getSale(DateTime StartDate, DateTime EndDate)
{
    string sql = "select * from Sale where date is not null and (date between @StartDate and @EndDate) order by date";

    //DON'T abstract SqlCommand/SqlConnection. DO abstract your connection string.
    //Also, don't bother with the try/catch at this level. You can't really do anything with it here, so worry about the exception in calling code.
    using (var cn = new SqlConnection(DB.ConnectionString))
    using (var cmd = new SqlCommand(sql, cn))
    {
        cmd.Parameters.Add("@StartDate", SqlDbType.DateTime).Value = StartDate
        cmd.Parameters.Add("@EndDate", SqlDbType.DateTime).Value = EndDate
        cn.Open();

        using (SqlDataReader rdr = cmd.ExecuteReader())
        {
            while(rdr.Read())
            {
                var sm = new SaleModel();
                //If you have good schema design, these values are **already** in the correct type. 
                // The old code forces an expensive conversion to string, following by an expensive parse back to the type it already had.
                // We can do MUCH better.

                sm.SaleId = (long)rdr["Id"];
                //but it is okay for types that are *already* strings
                sm.UserName = rdr["UserName"].ToString();
                sm.ItemsQuantity = (int)rdr["ItemsQuantity"];
                sm.TotalAmount = (double)rdr["TotalAmount"]);
                sm.SubTotal = (double)rdr["SubTotal"];
                sm.Discount = (double)rdr["Discount"];
                sm.Completed = (bool)rdr["Completed"];
                sm.Date = (DateTime)rdr["Date"];
                sm.CustomerPhone = (long).rdr["CustomerPhone"];

                yield return sm;
            }
        }
    }
}

这里再次没有所有额外的评论。这里的重点是，这仍然比使用字符串连接的原始代码少，并且编写时间不到 10 分钟。好的代码不一定需要更长的时间。

public IEnumerable<SalesModel> getSale(DateTime StartDate, DateTime EndDate)
{
    string sql = "select * from Sale where date is not null and (date between @StartDate and @EndDate) order by date";

    using (var cn = new SqlConnection(DB.ConnectionString))
    using (var cmd = new SqlCommand(sql, cn))
    {
        cmd.Parameters.Add("@StartDate", SqlDbType.DateTime).Value = StartDate
        cmd.Parameters.Add("@EndDate", SqlDbType.DateTime).Value = EndDate
        cn.Open();

        using (SqlDataReader rdr = cmd.ExecuteReader())
        {
            while(rdr.Read())
            {
                var sm = new SaleModel();
                sm.SaleId = (long)rdr["Id"];
                sm.UserName = rdr["UserName"].ToString();
                sm.ItemsQuantity = (int)rdr["ItemsQuantity"];
                sm.TotalAmount = (double)rdr["TotalAmount"]);
                sm.SubTotal = (double)rdr["SubTotal"];
                sm.Discount = (double)rdr["Discount"];
                sm.Completed = (bool)rdr["Completed"];
                sm.Date = (DateTime)rdr["Date"];
                sm.CustomerPhone = (long).rdr["CustomerPhone"];

                yield return sm;
            }
        }
    }
}

请注意，我 return 一个 IEnumerable 而不是一个列表。如果您真的需要一个列表（提示：您可能不需要，坚持使用 IEnumerable 会更快），您可以只对结果调用 ToList()。

Sql DataReader 有行但 Returns 有空数据

Sql DataReader Has Rows but Returns With Empty data

c#

sql

database

sql-server

sqlcmd