[英]Using MySQL Data Reader
I'm not familiar with using Data Reader, i need help with the following code, i want to retrieve a single data from the database. 我不熟悉使用Data Reader,我需要以下代码的帮助,我想从数据库中检索单个数据。
MySqlDataAdapter data = new MySqlDataAdapter(cmd);
conn.Open();
DataTable dt = new DataTable();
data.Fill(dt);
gridView1.DataSource = dt;
int retrievedValue = 0;
using (MySqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
if ((int)reader["order_status"] == 0)
{
retrievedValue = (int)reader.GetValue(0);
GridView View2 = sender as GridView;
e.Appearance.BackColor = Color.Green;
e.Appearance.BackColor2 = Color.ForestGreen;
}
}
}
reader["order_status"]
returns object
, since you told it is an already integer, you need to cast it to int
first. reader["order_status"]
返回object
,因为你告诉它已经是整数,你需要先将它reader["order_status"]
为int
。
You need to use ==
operator as well since it is a equality operator. 你需要使用
==
运算符 ,因为它是一个相等运算符。 =
operator is an assignment operator. =
运算符是赋值运算符。
if ((int)reader["order_status"] == 0)
Or you can use GetInt32
method with it's zero-based column number. 或者您可以使用
GetInt32
方法及其基于零的列号。 Let's say it's the first column that your query returns, you can use it like; 假设它是您的查询返回的第一列,您可以像使用它一样使用它;
if(reader.GetInt32(0) == 0)
By the way, if you wanna get only single value, I strongly suspect you may wanna use ExecuteScalar
method since it get's the first column of the first row. 顺便说一下,如果你只想得到单个值,我强烈怀疑你可能想要使用
ExecuteScalar
方法,因为它是第一行的第一列。 Then you can structure your query as SELECT order_status FROM ...
etc.. 然后,您可以将查询结构化为
SELECT order_status FROM ...
等。
Be sure to assign a variable before while (reader.Read())
otherwise it will and error. 确保在
while (reader.Read())
之前分配一个变量,否则它将会出错。 Then close the data reader once you are finished using it. 完成使用后,请关闭数据阅读器。 Like so:
像这样:
using (MySqlDataReader reader = cmd.ExecuteReader())
{
int retrievedValue = 0;
while (reader.Read())
{
retrievedValue = (int)reader.GetValue(0);
if (retrievedValue == 0)
{
GridView View2 = sender as GridView;
e.Appearance.BackColor = Color.Green;
e.Appearance.BackColor2 = Color.ForestGreen;
}
else if (retrievedValue == 1)
{
GridView View2 = sender as GridView;
e.Appearance.BackColor = Color.Red;
e.Appearance.BackColor2 = Color.ForestGreen;
}
}//and so on...
reader.Close();
}
I hope this is was you're looking for. 我希望这是你正在寻找的。
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