从本地数据库获取数据（.sdf） [英] get data form local database(.sdf)

问题描述

我正在使用 C＃Windows表单应用程序

我的程序将数据存储在本地数据库（.sdf）中。我不能从数据库中获取数据。

没有错误但没有从数据库中检索数据
这个我的代码这是我的第一个本地数据库程序

有什么不对？

有没有其他方法可以做到这一点？



表名= tbl_user

列名= u_name

 SqlCeConnection con =  new  SqlCeConnection（ 数据源= H ：\\application\\database.sdf）; 
 尝试 
 {
 SqlCeCommand com =  new  SqlCeCommand（  SELECT * FROM tbl_user WHERE u_id = @ u_id，con）; 
 com.Parameters.AddWithValue（  u_id， 1 ）; 
 SqlCeDataReader reader = com.ExecuteReader（）; 
  string  name = reader [  u_name ]的ToString（）; 
 MessageBox.Show（name）; 
 con.Close（）; 
} 
  catch （SqlCeException）
 {
 MessageBox.Show（  错误）; 
 
} 

提前感谢！

解决方案

首先应该更换

 SqlCeConnection con =  new  SqlCeConnection（  Data Source = H：\ application\database.sdf  ）; 

with

 SqlCeConnection con =  new  SqlCeConnection（ 数据源=   H：\\application \\database。 sdf  ）; 

并查看它是否有所改变。



字符串中的引号必须加倍或转义;反斜杠也一样。



你可以在这里找到参考资料：

字符串文字 [ ^ ]



[edit]



你似乎没有打开你的联系;这也可能是问题。

更好的处理方法当然是：

 使用（SqlCeConnection con =  new  SqlCeConnection（  Data Source =   H：\\application\\database.sdf   ））{
 尝试 {
 con.Open（）; 
  //   ...其余代码......  
} 
  catch （SqlCeException e）{
 MessageBox.Show（e.Message）;  //  这将是一个改进，而不仅仅是'错误'这个词 
} 
 } 

[/ edit]

它看起来读者没有获取数据
你应该这样做

string apppath = Application.StartupPath.ToString（）+\\Northwind.sdf;

SqlConnection con = new SqlConnection（Data Source = KTPL11 \\SQLEXP_KTPL11; Initial Catalog = Trial; Integrated Security = true）;



试试

{

con.Open（）;

SqlCommand com = new SqlCommand（SELECT * FROM tbl_user WHERE u_id = 1，con）;

com.CommandType = CommandType.Text;

com.Parameters.AddWithValue（u_id ，1）;

使用（SqlDataReader reader = com.ExecuteReader（））

{

string name =;

if（reader.Read（））

{

name = reader [u_name]。ToString（）;

}

MessageBox.Show（name）;

}

con.Close（）;

}

catch（SqlException ex）

{

MessageBox.Show（Error）;



}

I'm using a C# Windows form application
My program store data in local database (.sdf). I can't get data from the database.
No errors but no retrieving data from database
this my code this is my first local database program
what is the wrong ?
Is there any other way to do this ?

table name = tbl_user
column name = u_name

SqlCeConnection con = new SqlCeConnection("Data Source=H:\\application\\database.sdf");
            try
            {
                SqlCeCommand com = new SqlCeCommand("SELECT * FROM tbl_user WHERE u_id=@u_id", con);
                com.Parameters.AddWithValue("u_id", 1);
                SqlCeDataReader reader = com.ExecuteReader();
                string name = reader["u_name"].ToString();
                MessageBox.Show(name);
                con.Close();
            }
            catch (SqlCeException)
            {
                MessageBox.Show("Error");
               
            }

Thank in Advance!

解决方案

You should start by replacing

SqlCeConnection con = new SqlCeConnection("Data Source="H:\application\database.sdf"");

with

SqlCeConnection con = new SqlCeConnection("Data Source=""H:\\application\\database.sdf""");

and see if it changes something.

Quotes in a string have to be doubled or escaped ; and it is the same with backslashes.

You can find the reference here:
String literals[^]

[edit]

You do not seem to ever open your connection ; that can be the problem, also.
A better way to handle that would certainly be:

using (SqlCeConnection con = new SqlCeConnection("Data Source=""H:\\application\\database.sdf""")) {
   try {
      con.Open();
      // ... rest of the code ...
   }
   catch (SqlCeException e) {
      MessageBox.Show(e.Message); // Would be an improvement than just the word 'Error'
   }
}

[/edit]

it seeems that reader is not fetching data
you should do like
string apppath = Application.StartupPath.ToString() + "\\Northwind.sdf";
SqlConnection con = new SqlConnection("Data Source=KTPL11\\SQLEXP_KTPL11;Initial Catalog=Trial;Integrated Security=true");

try
{
con.Open();
SqlCommand com = new SqlCommand("SELECT * FROM tbl_user WHERE u_id=1", con);
com.CommandType = CommandType.Text;
com.Parameters.AddWithValue("u_id", 1);
using (SqlDataReader reader = com.ExecuteReader())
{
string name = "";
if (reader.Read())
{
name = reader["u_name"].ToString();
}
MessageBox.Show(name);
}
con.Close();
}
catch (SqlException ex)
{
MessageBox.Show("Error");

}

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